Training For Professional Performance
This manual is one of a seri es for your use in learning more about equipment that you wo rk with in the oilfield. Its purpose is to assist in developing your knowledge and skills to the point that you professional manner.
In order for you to learn the contents of the manual, you must dig out the pertinent facts and relate them to the subject. Simply reading the material and answering the questions is not enough. The more effort you make to learn the material the more you will learn from the manual.
The manual was prepared so that you can learn its contents on your own time, without the assistance of an instructor or classroom discussion. Educators refer to learning by self -study as Programmed Learning. It is a method widely used in all industries as a means of trai ning employees to do their job properly and teach them how to perform higher rated jobs.
Teaching yourself requires seifdiscipline and hard work. In order to prepare yourself for the sacrifice you will have to make, you should set goals for yourself. Your ultimate goal is to perform your work in a more professional manner. Training is one step in reaching tha t goal. Application of what you learn- is another. Seeking answers to questions is a third.
You can demonstrate your desire to be a professional by taking a positive attitude toward learning the contents of this manual and others that are applicable to your job.
Once you have established your final goal, you must determine the means for reaching that goal. You may decide, for example, that you must complete a series of 10 or 15 manuals. to get the basic knowledge and skills you need. After you decide which training mate rial is required, you should set a time table for completing each section of the material.
can
perform
your
work
in
a
more
The au thor of tliis manual has years of experience in operating petroleum He also has t he tech nical equipment. knowledge of how and why petroleum equipment functions. The text was written _ . for use by personnel with little or no ? previous experience with petroleum equipment. Consequently, some of the mate rial may be familiar to yo u if you have experience with oilfield equipment. From such experience, you have observed the effect of making operating changes. The manual will help explain why the changes occurred that you observed. It will also teach you how and why equipment functions.
Achieving your final goal may take more than a year, and will require hours of hard work on your part. You will know you have achieved your goal when you understand how and why to operate oilfield equipment in order to obtain the maximum product at the lowest cost. Your sacrifice will have been worth-while from the satisfaction of knowi ng that you can perform your job in a methodical professional manner, instead of a trial-and-e rror-approach.
Instructions For Using This Manual This is your manual. You should write your name on the cover. Upon completion you will find it helpful to keep it in an accesslble place for fu ture reference. Problems may be included throughout the text. The solutions to the problems are given at the end of the book. The manual is used in traini ng programs all over the world. In some countries, English of measurement such as feet, gallons, etc., are used. In other countries Systems Internationale (SI) or Metric units, such as meters, liters, kilograms, etc., are used. In order for the manual to be of maximum use, both SI and English units are shown.
The following general procedure is recommended for using this manual :
1.
Turn to Page 1. Read the material until you come to the first problem or question.
2.
Work the first problem or answer the question and enter the answer in the proper space in ink. If the problem or question is shown in both SI and English units of measurement, answer only t he part in units of measurement tha t you use.
3.
Compare your answer with that shown at the end of the book; be sure to use solut ions to the problems in the units you are working in.
The SI unit always appea rs first, and the English unit follows in brackets []. Example: the temperature is 25'C [77'F], The English equivalent of the SI Unit will be rounded off to the nearest whole number to . plify the text and examples. A distance of m may be shown as 33 ft when the exact equivalent is 32.81 f1. If you are working in English umts, you may find it helpful to mark out the parts that are in SI units, and vice versa. Some of
the Figures have units of ~ 'ffieasurement. In such cases, two Figures are included. The first one has Sl units, and the Figure number is follow ed by the .letter A (Example: Figure lA). The second Flgure wllI be on the next page and will have English units. It will be the same number as the first one but it will be followed by the leiter 8 (Figure 18). If you use SI units, be sure to refer to Figures followed by the letter A; lf you use English units, refer to Figures followed by the letter 8.
If your answer is correct, continue reading unti 1 you come to the next problem and work it. If not, restudy the manual until you understand th e reason for your error. Rework the problem if necessary. Leave your wrong answer and note the correct one. This will keep you from making the same mistake later on. 4.
Proceed stepwise as shown above until you have completed the text.
The above approach will require thought, mak ing mistakes, and re t hinking the situa ti on. Concentrate on two things - the how and the why. Do not cheat yoursel f by taking shor t-cuts or looking up the answers m advance. It saves time and errors but produces no real understanding. Your future depends on how efficlentl y you perform your job and not on how rapidly you proceed t hrough this manual. Since this is your manual, any errors you make are private.
Abbrevjations Used In This Manual
Units Of Measurement
SI UNIT ABBREVIATIONS
SI UNITS OF MEASUREMENT
s, min h, d mm cm m km • 2 m m'
m'ld L g kg kPa MPa kPa(a) bar kJ MJ W,k W M
second, minute hour, day millimeter cen timeter meter kilometer square meter cubic meter cubic meters per day liter gram kilogram kilopascal megapascal kilopascal absolute bar (1 bar = 100 kPa) k ilojol~ e
megajoule watt, kilowatt meta
time time length leng th length length area volume volume rat e
MM
METRIC UNIT Pressure bar
SI UNIT
weight weight pressure pressure pressure pressure hea t, work heat, work power million
time second, minute t ime hour, dgy length inch, foot area square inch square foot area volum e cubic foot volum e gallon volume bal'rel (42 US gal) volume rate barr els per day weight pound pressure Ibs per square inch Ibs per sq in absolute pressure British thermal unit hea t thousands of Btu heat hea t millions of Btu power wat t , kilowatt power horsepower gas flow ra te cubic feet per day gas flow ra te thousands of cfl d gas flow rate millions of cfl d thousand million
Hea t
CONVERSION
ki lopascal, kPa bar =
volum e
ENGLISH UNIT ABBREVIATIONS s, min h, d in, ft sq in sq ft cu ft gal bbl BPD Ib psi psia Btu MBtu MMBtu IV , kIV hp d id Md/d MMcf/ d M
Most of th e SI units of measurement used in the oilfield are traditional metric units. The exceptions we are concerned wi th are pressure and hea t units, which differ as follows:
kil oca l kilojoul e, kJ
kPa
IOU
kJ kcal =[2
STANDARD CONDITIONS FOR GAS VOLUME Measuremen t units for gas volume are cubic met ers (m ' ) or cubic feet (cf). Th e lett ers st or s are some times used with t he units to designate volume at standard temperature and pressure: m ' (51) or scf. In this manual, st andard volumes are corrected to a temperature of 15 °C and a pl'essure of 101.325 kPa(a), or GO °F and 14.7 psia. To si mplify the tex t, the letters st and s are omitted However, aU gas volumes shown are at st andard conditions unless specifica lly stated otherwise.
HEAT CAPACITY AND REL ATIVE DENSITY Specific heat and specific gravity are traditi onal t erms that have been used in both Metri c and English uni ts for many years. Th ese names are being I'eplaced with th e words: hea t capacity and relative density. The new names are used in thi s manual. Wh en you see the term hea t capeci ty (H t Cap), it will have the same meaning as specific heat; and rela ti ve density (ReI Dens ) means specific gravity.
CENTRIF UGAL PUMPS
TABLE OF CO NTENTS
INTRODUCTION ...... . ......... . ... ... . . .... .. .. . . . ... . ..... . ...... I I.
DESCRIPTION OF CENTRIFUGAL PUMPS... . . .. . . ... . . . . •.. . .. . . .. 2 A.
Basic Pump Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . 2 1.
B. C. D. II .
III.
. ... ... . .... . ... ... .... . ... . . . .. . . .. . ... .... . . . . . . 2 Impeller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Shaft. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Bearings . ..... . . _. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. 3. 4. 5. Seal or Packing . .... . .... . ............... . ... .. . .. . . ... . 3 Couplings ... . ....... . . . ...• .... .. .... . .. ... .. .... . . . .. . .... 4 Types of Cent rifgual Pumps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6 Alternate Sealing Systems . .............. . . . .. . . . .. .. ... .. .. 10
PRINCIPLES OF CENTRIFUGAL PUMPS . . .. .......•....•......... 14 A. B. C. D E F.
Flow Through Pumps ............ . . .. . . .... ... .. ... . .. . ... ... Centrifuga l Force ... ... . .... ....... . ................ . .... . Head Pressure . ....... . ... . ..... .. ....... . .........•... .. ... Cavitation a nd Vapor Lock .. . . . . ... ............. . . . ........ . Performance Curves . . . . . .. .... . ..... . ... .... . ... .... .. .. ... Pump Efficiency ... . . .. . ... . ... . ..... ... ... . ......•. . .. . ...
G.
Driver Power .... .. ...... . ....... ... . . . ..... .. .. . . . ...... . . 24
H.
Liquid Suction Head
I. J.
Thrust . . ... .. . . . ... .. .. . . " ... ... .. . . . ..... .. ... . .... .. . . . 27
14 14 16 17 19 21
............ .. . ... . ... . .. ......... . . .... 25
Pump Curve Application
.. ... . .... .. .... . .•... . .. .. .. ... . . . . 29
OPERATION .... . ... . .. .. . .... . .... .. ... ... . ... . . . ... . . .. .. .. .. 35 A. B. C. D.
IV.
Case
Start-up Procedure . .... . . .. •.. . . . ..... . . . . .. . .. .... . . . . .. .. Control of Pump Flow Rate . . . . . . ... ... ... .. .. .. . .. .. . ... .. .. Shutdown Procedure ............ . ... ... .. .. ... ... .. . ........ Routine Operating Checks .. . .... . .... . . ... .. ... . .. .• . .. . .. ..
35 36 40 41
TROUBLESHOOTING .. . . .... . .. . ......... . ...... . . . ...... . ..... 42 A. B.
Troubles hooting Procedure for Vapor Lock . .. . . . . . . . . . • .. . ..•.. 42 Troubleshooting Procedure for Low Flow Rate .. . ......•........ 43
VALIDATION, SI UNITS .... . ... . .......... ......... . .. . . . ... . .. .. ... 45 SOLUTIONS TO PROBLEMS, SI UNITS . . .... . .... ... .•.. . . . . . .. . .. . ... 46 VALIDATION, ENGLISH UNITS
........ .. ... .. . . . . ... . . . . . . .. . . ... . .. 47
SOLUTIONS TO PROBLEMS, ENGLISH UNITS
............ . ........ ... . 48
LIST OF DRAWINGS, GRAPHS AND ILLUSTRATIONS
..... ... .............. . .. ......... ... .. ..... . .. ........
Impellers
2
Cut-away Picture of Pump
3
Packing and Seals
.. ....... .. .... .. .. ....... . .. .. ... . ............. .
4
.... .. . ... ... .... ... .. ... . ........ ..... . .. . ............
6
Couplings
Pump with 2 Seals . . .................. ... ... . .. ... .... .. . ...... .. . 10
Seal Oil Pots
. . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. 11
Circulating Seal Oil System
13
Flow Through P-um p ... .... . . ......... .. .... .. .... .. . . . .... ...... ... 14 Head Pressure
. .. . .......... . . ..... ..... .. . .. . ........ . . . ..... ... 17
Procedure to Clear Vapor Lock 18 Pump Performance Curves .• . ... .•. .. . ..• .. . . ..... . ... . .... . 20, 22, 23 Liquid Suction Head Thrust
.•....... • .. . .... •. . .... ... .... ....... . . . .. ... 26
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..
27, 28
Balance Piston . . ... . .... .. ................ . .. .... .. .......... . ... 28
Design Conditions for Stabilizer Feed Pump .. . .. . .. .... . .•........... 29 Performance Curves for Stabilizer Feed Pump
...... •. . .. • ....... . 30, 31
Start-up Procedure .............. • .... .. ........ . .•............. . Flow Control with Control Valve in Discharge Line Regulated with Level Controller
35
. .. ... .. .. .. .. .. . .. 36
Flow Control with Control Valve in Discharge Line .. ... ........ . .. .. , 37 RJ',!/ulated with Pressure Controller Low Flow Recycle .. ........ .. .•.. ...•. .. . ........ . •...... • ... . .. 38 Flow Contl'ol By Changing Driver Speed
... ........• .. . . •.. . ....... • 39
Effect of Pump Speed on Capacity, Pressure Head and Power . .. ... ...•. 40
CENTRJFUGAL PUMPS
INTRODUCTION
Pumps are used to force a liqu id to flow from a point of low preso,;;ure to one of highcr p,·c,-,u,·e. Ther Are two general cia
ifieutions o f pumps:
l. Positiv e Displuc mcnt Pumps
2. Centrifugal Pumps In thi., manual we will di ... cuss the Ccnlr'ifugal Pump. Posi tiv e Displacement Pumps
are discussed in Manual £-17 .
NOTE :
Thi s manual includes bo t h SI and Engli sh Units of measurem ent. I f you use English Unit ... , disl'egard the i\ietl'ic Units, and vice ve rsa. Refer to the instruc t ion page at the front o f the manual.
. . .
••• CENTRIFUGAL PUMPS
I. DESCRIPTION OF CENTRIFUGAL PUMPS
2
A. Basic Pump Parts A t ypical Centnfugal Pump is show n on the opposi t e page,
It has fi ve basic parts
which arc deseribed below : l.
Case - The pump ease
01'
othel' par'ls arc enc losed within it. other special mAteJ'ials.
casing is the visible part of the pump,
Most of the
It is usuAlly made of case iron or steel, plHStiC, or
1n the oilfie ld, casings on pumps operating at 8 pl'essure below
1000 kPa'[150 psiJ usually arc made of cast Iron,
Pumps opel'ating at highel' pressu ]'e
generally will have casing made of steel.
2,
Impeller - The Impelle]' is the part of t he pump that causes the liquid pl'essul'e to
rise, It is fu'mly attached to the shaft with a key and/or pI'essed on the shaft, It rotat es inside the case at the speed of the shaft. l'he Impeller on most oilfield pumps is made of cast iron . However', stainl ess steel, pla~llcl
or oUler' special ma ter ialS ca n be used for corrosive or chemical serv ice. 'J'h€!'c
are two gener.1 types of Impeller's; the open vane and the closed vane, The closed vane develops a higher pressure, but has a lower capaci ty.
CLOSED VANE IMPELLER 3,
OPEN VANE IMPELLER
Shaft - The shaft I'otates inside the case at the speed of the dl'iver, It usually is
made of .teel.
The portion or shaft exposed to the seal
01'
pack ing may have a sleeve
made of some hard metal, such as tungston carbide, to resis t corrosion or
WeBI'
at tl1a t
point.
-t.
Bearings - Bearings serve two functions on a pump:
a, To hold the shaft so that it does not wobble inside the pump easing, b, To prevent lateral movement or the shaft so that the rotating par ts do not touch the pump casing,
Th,'ust forces, developed as the impeller I'otates, are the main
PUMP PARTS
3
- --.
Bearings
Case
Shaft Seal
PARTS OF CENTRIFUGAL PUMP
cause of lateral shaft movement.
One or more of the bearings must be designed to
withst and the thrust forces . On small process pumps, the bearings may be contained in the pump casing. On larger pumps, the bearings are contained in housings located on one or both ends of the shaft. The bearings reqUIre lubrication.
The bearing housing shown above
is partially
filled with oil for lubricatrion. A sight glass indicates the level of oil in the housing. The bearings shown on the end of eacll shaft on Page 5 are a grease lubricated type. 5. Seal or Packing - The seal or packing is used to preven t liquid under pressure inside the pump from leaking out the pump. The mechanical seal is used in most oilfield cen trifugal pum ps. components:
It has two basic
PUMP PARTS
4
Sea l Gland Stationary Sea l Ri ng Rotating
fni~i;;z:;~seal Ring
,"
PACKING RINGS
Sha ft
MECHANICAL SEAL
a. 1\ statiooary ring thll t is secured in the sea l gland. b. A rotating "ing that is part of tile sea l element attached to the shaft. One of the seal ri ngs is made of cal'bonj the other is made of hardened steel, ceramic
Ot'
othe r speci al non-cor r'os ive material. Some seal manufacturers use a carbon
stati onary ring and oth er's a cHrbon "otating ring. Pack ing often is used in low pressUl'e service, or in pumps handling abrasive liquids such as mud or s]urr'y. P ac ~ ing
is composed of a series of pliable ri ngs contained in a packing gland. The
.. ings arc comp ressed by tighte ning the gland nuts. Th is squeezes the dngs aga inst the shaft and p,'events liq uid fro m leak ing ou t, "'Iecilanical seals generally req uire much less mainte nance than pack ing, so they are used whenever poss ible. When they are used, liquid must be free of sand, dirt, or other so lid partic les tha t
CUll
scratch the seal faces and cause leakage.
B. Couplings
The pump sha ft connects to the driver with a coupling. Coup lings trans mit ,'otation from the dri ver sha ft to the pump shaft. If a gearbox is between the drive,' and the pump, a coupling attaches the dr ive,' shaft to the inlet gearbox silaft. alld another coupling attaches the outlet bearbox shaft to the pump shaf t.
COU PLIN GS
5
Bearing s Coupling
The couplings ill ilst be able to withstand the shock of a sudden change in pump load, 0 1'
stoppage of t he dr ivel'.
They must be flexible enough to t,' ansmit power from the
dri ver to t he pump at high speed when the two shafts al'e not pcl'fectly al igncd, In fact, it is almost impossible to perfectly align the two shafts, because the operati ng tempel'a ture diffel'ence between the d,' iver and pump resul ts in one expanding slightly more than the otehr. The coupling must be able 10 1wobble' enough to overcome the misalignment.
Some of the more com man types of coupli ngs are shown on Page 6. In each type, the drivel' shaft attaches t o one half or hub of the coupling, and the pump shaft att aches to the other. The shafts al'e usually keyed to the coupling hubs.
Pl'oblem 1 Match each itcm in the column on the rig ht with one on t he left. Im pe ll er
a,
Prevents liquid inside pump f rom leaking out.
Case
b,
Pre ven t shaft movement.
Seal
c,
Connects pump and dr iver,
Shaft
d.
Open or closed vane,
Bear ings
e,
Rotates inside pump.
f,
Enclosure for rotating pump par t s.
__ Couplings
Ii
PUMP TYPES
FLEXlflU DISC COUI'UNG \ lubs attach to compo sitIOn di:.;cs that arc
casily replacl:d.
Hub
Sleeve CR It) COU,'UNG Hubs art" se rpent I
fils
'"
GEA R COUPLING
·;'".hed
with ,, ;"lng that
il' :";IU:~ In
Hubs with gear t eeth me sh with sleeves having rnatching t eeth.
each hub.
c . Types of Cent r ifugal Pu mps (\,'Iltl'igu:d pumps can eithC'1' be hOl'jzontaJ or vCl'ti('ul. Tht' hOl'i7Clnla Lpump I'l'quircs l:
'~rll'
plpirl~.
'olillda li on ror its mounti ng.
wh e r' ea~
the vertical pumr Can he nttaeilcd to the
l-.ilil 0 minimum of support bcnenth the pump.
/,i! ~~gvd P1lillp
The horizontal pump is 11 more
wl1i('11 will I'c~js t any vibration present.
V('I'll(,'al pump" are commonly used in process ph-Jots i n IOt'ations where vibrution is :!I)t "pf'Obk nt. I\nolilel' advantage or the vel' tical pump is thul the ulignlTlen t bf'twcen the !110({'I[' lind Dump
j-;
much easier to maintain than that of the horizontal pump.
7
PU MP TYPES
HORIZONTAL PUMP
VERTICAL PUMP 1. Mu l tistage Pumps As we win learn later, there will be occasions when 2 or more impellers are needed
for the pump to delivel' the required presslIre. called multistage pumps. impe llers is
Pumps with more than one impeller are
Each impellel' is referred 10 as a stage.
A pump with 5
a 5-slage pump.
There are three common types of mu lli-slage pumps;
1. Submersible
2. Can
3. HOl'izon tal The submersible pump is an integral pump-motOJ' un i t in a sealed enclosure. well, Ihe pump is insert ed inside the casing. tile motor.
In a
An electric cable runs from Ihe surface to
These pumps are used for lifting watel'
OJ'
oil from any depth.
The pump
capacity is limited by the size of the casing. For example, a submel'sible pump which will fit inside a 20 cm [8 inch J casing will deliver a maximum now rate of about 68 m 3/d
[300 gplll
J.
An electr ic power source is required to operate the pumps.
8
PUMP TYPES
C AN TYPE: VER TIC AL PUMP
SUBMERSIBLE PUMP
9
PUMP TYPES
HORIZONTAL MUL TlST AGE PUMP
Can-type Pumps are used to 1ift liquids from storage tan ks or sub-sur race sources.
The pump driver is located at
01'
above the liquid surface, and the shaft extends f rom the
driver to the pump, which may be located some dist ance bel ow the liquid sUt'face,
Th is
type is used f requently on offshore pl stfol'ms to provide an emergency f irewatel' supply, Both the can and submersible pumps can have up to 60 stages or impellel's, depending upon the depth at which thc pump is se t. [f one impeller developes a pressure rise of 1300 kPa [43,5 psi], and a total pressure rise of 9000 kPa [1305 psi J is I'equ ired to lift the liquid to the surface, then the number of st ages wi ll equal: SI UNITS
ENGLISH UNITS
T otal P['essure Requ ired
9000 kPa
1305 psi
Pl'es;ure rise pel' stage
360 kPa
43,S psi
Number of stages
9000 = 30 300
1305 = 30
43.5
Horizontal multistage pumps are used in process plants and oil pi pelines where th e pump must raise the liq uid pressure seve!'al thousand kPa [sevel'81 hundred psi]. Thel'e is no lheoreticallimit to the numbel' of impeJlers in 8 hori zonta l pump, but more than 8 are
seldom used,
SE AL SYSTEMS
10 D. Alternate Seal Systems
A pump handling liquid hydroca rbon can cause a hazardous situat ion if hydrocarbon
leaks out the pump seal to t he surrounding atmosphere. One way to avoid this is to install tw o seals on the pump wi th a pressure guage between the two. When the inner seal starts leaking, pressure will rise between the two seals and it can be observed on the pressure gauge. In so me cases, a press ure swi tch is provided between the two seals so that a rise in pressure trips the switch a nd s ignals a n alal'm or may even shut dow n the pump.
Rise in pressure between
seals indicates leaking inner seal.
Impeller
Shaft
Inner Seal
Outer Seal
PUMP WITH TWO SEALS Anot her way to prevent liquid inside the pump from leaking to the atmosphere is that of using a seal oil system, which also has two seals. A simple seal oil system is shown opposite. There are two sea l oil pots with water in lhe bottom of lhem. Pump discharge liquid fills one pot above waler level; the other pot is filled above lhe waler level with seal oiL The seal oil is piped to the space between the two seals on lhe pump. Water in the bottom of the pots preven ts pump discharge liquid fro m mixing with the seal oil. Since pump discharge pressure is imposed on the seal oil pots, the press ure in the pump seal oil chamber (bel ween the two seals) is pump discharge pressure. The purpose of the bypass line is to allow liquid on l he pump side of the inner seal to flow inlo the suction side. This will hold the presure on the pump side of the inner seal at suction pressure. Pressure on the other side of lhe inner seal is pump discharge pressure. Wilh this arrange ment, a leaking seal will resull in seal oil leaking into the pump, becau e
SEAL SYSTEMS
11
Pump LIquid At Dllctl.rge Pre"ure
I J BypllSil
SEAL OIL POTS
Used for IiqllLd CW"I In! PlIrT"9 side 01 the inoel Jeal 10 flow
to the aoction tide of the pump, This Jowerl press"re on pump .ide of IlYler IIIal to lion prfllllUtt.
~~
_ _ _ ..bd-.. __ ..-.
Inne r Seal
---.
Seal Oil Chamber
ll;!akirw:l see! will result in Ioeel oil lellking into pump.
l eak ing aeal wlU Te...,lt in luI oil leelcing into lilt atmosphere.
SIMPLE SEAL OIL SYSTEM PUMP WITH SEAL OIL POTS seal oi l press ure is higher than pressure on the pump side of the seal. The outer seal is prov ided to prevent seal oil from leaki ng to the atmosphere. The seal oil pots are used on small process pumps - usually less than 35 kw [5 0 hp J. The effectiveness of the system is limi ted by the volume of sea l oil conta ined in t he system . If a large leak occurs in the inner seal, pump discharge liquid will even tu ally displace sea l oil in the pots, and the liquid between the two seals will be pump liquid. In th is sit uat ion, failure of the out er seal will result in pump liquid leaking to the surrounding atmosphere and crea te a hazard. Lal'ge pu mps hand ling vo latile or hazardous liquids are often eq uipped with a circulatirg seal oil system as shown on page 13. This system has two pump seals just as the sea l oil pot system did. The primary difference is tha t seal oi l is cont inuously pumped through the seal chamber at a pressure higher than the pressure inside the pum p, pressure controU er in the seal oil outlet line is set to hold this desired press ure.
A
12
SEAL SYSTEMS
The drawing on the opposite page shows a mult i-stage pump with a balance piston used to offset thrust for ces in t he pump.
Pressure on the ou tboard side of the balance
piston is held at suction pressure by allowing liquid that leaks across the balance piston t o flow back to the suction side of the pump t hrough t he balance line . This particular pump has scals at each end of the shaft. The bal ance line holds suc t ion pressure on the pump side of both sea ls. Consequently, as long as the sea l oil pressure is above pump suction pressure, leaking seals will result in seal oil leaking into the pump rathel' than pump liquid leaking to the seal oil system. Seal oil is a non-volatile liquid that docs not contaminate the liquid inside the pump when it leaks into it. Some fOI'm of lubricating oil is often used for seal oil in hydrocarbon pumps.
PI'oblem 2 List th type of pump and seal to use in the follow ing serv ices:
Service a.
Process pump used in gasoline plant
b.
Pump water from a well
c.
High pre ssure cI'ude oil pipeline pump
Pump Type
Seal
located in an enclosed building d.
Fire water pump on offshore platform
CENTRFUGAL PUMPS USED IN ffiACTIDNA TlNG SECTION 0; REFINERY
13
SEAL SYSTEMS
PRESSURE CONTROLLER
l
1 DISCHARGE
SEAl.. OIL COOLER
WATER
t
flLTERS SEAl OL TAN<
F'l.MP
SEAL OIL SYSTEM
14
D. PRINCIPLES OF CENTRIFUGAL PUMPS
A. Flow Through Pump Liquid enters the pump at the eenter or eye of the impeller. In most process pumps, the impeller rotates at a speed of 1200 to 36.00 revolutions per minute. At this speed, the liquid enters the center of the impeller and is thrown into an enlarged chamber called the volute. Liquid flows around the volute and exits in the outlet nozzle. Liquid Outlet .
Liquid • Inlet
b=l,,'; ~F
1?~--;r.I---lmpeller-----t7t--"'*'
-n'f----Volute------+_
UQUJD FLOW IN CENTRIFUGAL PUMP
B. Centrifugal Force Suppose you take a bucket that is almost completely filled with water and swing it in a circular motion around your body. If you swing it very slowly, some of the water will spill out of the bucket. However, if you swing it fast enough, none of the water will spill out of the bucket. The centrifugal force generated by swinging the bucket pushes the water against the bottom of the bucket so that it does not spill out. Now suppose we have a small hole in the bottom of the bucket. As you swing the bucket, water will come out of the hole. The faster you swing the bucket, the farther the water will travel that leaves the bucket. This is the principle of centrifugal action. When you move the bucket fast, you use more energy. The distance that the water travels from the hole in the bucket will depend upon the amount of energy that you use in spinning the bucket. Before we attempt to understand the principle of centrifugal pumping, let us look at the pump unit first. It includes a driver and a pump. The energy used by the driver -
CENTRIFUGAL FORCE
15
motor, turbin e, or engine - is transferred to liquid in the pump in the form of pl'essure by
the pump. In other words, a pump is a device for transfer ring energy from the driver to t he liquid. It is important that we recognize that energy is enter'ing the liquid in order to under'stand pumping. El ectri c energy used by a motor-driven pump is transferred to liquid by the pump in t he form of pressure. Another thing we need to realize is that ener'gy can exit in sever al form s. A ri fle shell contains ener gy in the form of powder .
When t he shell is fired, energy
burning powder transfer s to the bullet in the form of velocity.
of th e
That energy converts to
pressure when t he bullet strikes an objec t and l oses its velocity.
Vel ocity energy is
converted to pressur'e energy, A cen trifugal pump uses the same velocit y-pressure concept to mise liquid pressure. Liquid enters an impeller at the eye.
The speed of the impeller' Cl'eates a cen t rifuga l .
16
HEAD PRESSURE
force that throws the liquid to the outer edge at a high velocity. It leaves t he
i,~p e ll er
at
high velocity and enters the volute, which is an en larged chamber where the velocity is quick ly reduced. This veloci ty reduction results in a pressure increase. The liquid flow ca n be compared to that of the moving bullet .
The now in the
impeller at a high veloc ity cor responds to the movement of a bullet through the air. The liquid slow ing dow n in the volute with a resultant pressure rise is comparable to the force of a bu llet striking an object. The amoun t of pressure an impeller will develop depends upon its diameter and the speed at which i t rotates.
A large di ameter impeller operat ing at a high a speed will
develop t he highest pressure.
The p"essure developed by the impeller is l imited by the
materials of which the impeller is made. It is subjec t to the sa me cen trifugal force as the liquid and will fly apart if the cen tr igual force is excess ive.
If a si ngle impell er will not develop thc p" essure requi"ed, two or more impellers can be inst alled in ser ies to increase the press ure rise across the pump. A pump with three impellers can be compared with t hree pumps which operate in series.
Discharge liquid
from the first pump enter s the second one, and liquid from t he second pump flows to the third one. There is no theoretical limit to the number of impell ers which can be instaUed in a pump. However, horizontal pumps seldom have more than eight impeUers in one casing. If this is not enough to produce the desired pressure, a second pump will be used. Submersible or can pumps can have 50 or more impellers. Vertical pumps are usually built in segments, so t hat there is no theoretical mechanical lim it to the number of impellers which can be installed. C. Head Pressure The purpose of a pump is to raise the pressure of liquid. The amoun t of pressure rise is called the head pressure, or si mply head
It equals the discharge pressure minus the
suct ion pressure. The pressure developed by the pump - head pressure - will be constant fOl' any suction pressure. In other words, a pump that develops a head pressure of 300 kPa [45 psi], wi ll ha ve a discharge pressure that is 300 kPa [45 psi] more than the suction pressure, regardless of wha t the suct ion pressure is. Obviously, the pump casing must be designed to withstand t he highest discharge pressure expec ted in the servi ce for which i t is used.
17
CAVITATION AND , VAPOR LOCK
It is important that you remember the t er m head pressure, as it will be used frequently in the following discussions. Suction Pressure ·
Sue t i on .1IIIII.1IIIII.1IIiII1IIIII.1II!~1 Liquid
DIScharge Pressure
Discharge 11IIIII1II!1IIII1III1IIIII1IIIl1IIIII1IIIII-. Liquid
CENTR IFUGAL PUMP
HEAl) PRESSURE
= DISCHARGE PRESSURE - SUCTION PRESSURE
Problem 3 The discharge pressure gauge on a pump reads 1000 kPa [145 .psi J. . Suclio.n pressul·e . is 400 k.Pa [58 psi _ _ _ kPa
J. The head pressure developed by the pump is [psi J.
D. Cavitation and Vapor Lock Cavitation and vapor lock are ter[lls often used interchangeably to describe pump failure due to the presence of vapor in it.
Although caviation and vapor lock, both occur
when gas is present in a pump, they each have different effec ts on the operation of the pump.
Cavitation occurs when the liquid entering a pump contains a few bubbl es of gas. The gas flows through the impeller with th e liquid and as its pressure is increased in the pump, some or all of tti", gas ·liquifies (the vapor ' bubble.s collapse.)
A high centripetal
force results from this collapse and. m·ay ;cause severe vibration and poss ible pump damage. The pump will continue to ·pump liquid, but it will be noisy and may vibrate.
Vapor lock occurs when gas. enters the pump· with liquid and separates from the liquid inside the pump and fills all ar a part of the pump. The pump will compress the gas a slight amou nt, but not nearly enough for tlie gas to flow out the. discharge line. tr~pped gas prevents liquid
through the pu mp.
The
tram entering .t he pump. The effect is that no liquid flows
-
VAPOR LOCK
18
When a pump vapor locks, the discharge pressure gauge reads about the same as suction pressure while the pump is running.
In order to clear the conditi on, the vapor
must be removed from the pump. In some cases, this can be done by opening a vent valve while the pump is r unning. Quite often, the pump must be shutdown and the casing vented unti l liquid flows out the vent line. At this point, the pump is restarted. Some pumps are more prone to vapor lock tha n othe rs.
A procedure for starting
these pu mps is: 1.
Close a val ve in the discha l·ge line. Suction valve is open .
2.
Open the casing ven t valve until a steady strea m of liquid comes ou t. Partiall y close the vent valve, but keep a steady steam of liquid flowing.
3.
Start the pump and observe the discharge pl·essure.
It should rapidl y increase
and then level off. 4.
Slowly open the valve in the discharge line.
5.
Close the valve in the vent line .
Observe the disoharge pressure during Step 4.
If i I drops to suction pr essure, the
pump has vapor locked again, and you will have to shut it down and start over.
cP r.M.l
SUCTION
Sto" d,I .. ,
la~ :
)
Open "eot ",lve uotU 1[811dy
.tream of liquid come. out.
8
Open .... 1.... in IlUCtion line ~--'-----...
1
1-------'
5 Quer ... e dllch8rqe preMUU!. /~""" ": /I t ahoi,Jld rill! rapid ly and then level off. Slowly open .... I... e In dischllrge line.
PROCEDlRE TO START - UP AFTER CA VIT AnON
Cavitation or vapor lock occur when gas is present in the pump. A few gas bubbles will cause cavitation. More will cause vapor l ock. Both are prevented by preventing gas from entering a pump. This can be done by raising the suction pressure to the pump, or raising the l evel of liquid in the vessel that is being pumped.
PERFORMAN CE CU RVES
19
E. Performance Curves
It will help us in operating our centr ifugal pumps i f we understand how pumps are selected in the fi r st place, and what their operati ng limitations are. Suppose have need for a centrigual pump that will operate at the follo wing conditions: Flow Rate :
40 m J I hr [ 17 5 gpm]
Head Press ure:
600 kPa [ 87 psi]
Relat ive Densit y of Liqu id:
0. 80
Maximum Discha rge Pre!)'Sure:
3450 kPa [5 00 psi]
We give thi s inform at ion to a pump manufacturer and t ell him to supply us with a pump driven by an elec tric mot or. The manufacturer has a number of st andard size pump casi ngs and impell cl·s. He must selec t the standard unit that will fit our des ign conditions and operate at a high efficiency so that we don't wast e a lot of elec tricity in dri ving the motor. We wi ll discu ss efficiency later. The pump manufact ure r has pel'formance curves fOi' cach standard si ze pump that he makes. These curv es show the relation bet ween flow rat e and head pressure f or differe nt size impellel's operating at differen t speeds tha t can be used in the same pump ca sing. Typica l cUI'ves for a pump operati ng at 35 00 rpm are shown on the following page. The top curve is for the largest diameter impeller that can be used in that pum p casing. It has the highest head pl'essure of any of the impellers. It also requires the largest driv er. The bottom cu r ve shows t he smallest dia met er impell er wh ich can be used in that pump casmg.
In our application, a 200 mm [8 in] diamet er impeller will deliver th e head
pressure at the flow rate we have spec i fi ed.
This will be the size impeller that the
manufacturer wiU use in our pump.
The pump curves show the head pressure t ha t different sizes of impellers will develop at various flow I'ates at a 3peed of 35 00 I·pm . A di ffer ent se t of curves for the same casing and impellers wi ll apply at a speed other than 3500 rpm .
As the speed is
reduced, the head pressure at a given flow ra t e will be less. We will discuss the effects of speed later.
For the time being, we wi ll confine our discussion to pumps operat ing at a
const ant speed. The pump manu fac turer uses the pump curves to select the pump casing, impeller size, and speed that will sa t isfy our process requ irements at the lowest pow er consumption by the driver.
PERFOR MAN CE CU RV ES
20
51 UNITS
, 230 . _ Iotl.O _ _ ,JA",·'r,·, '"
800
' IMPELLE R
,
,.
,"
215 lotH
"t
-,, t .,
OES TG
POINT'
500
4 00
.,
, ..
., I
0
-
,
20
10
, 1 - ..! -
,.
:
30
40 PU-1P C APACITY, M I /Kt
ENGLISH UNITS
,. i
11 0
.. 100 T
., . . 71.
"1
'\
INC"
..
S I GNPO I NT
,. , ~
7
'
_.
60 0
T
' ,. I",
3500 RPH
t 50
100
150
200
250
'00
CAPACITY CLRVES FOR VARIOUS DIAMETER IMPELLERS IN Sf ANOARD PUMP CASING AT ) 500 RPM
350
21
PERFORMANCE CU RVES
The pump cUi'ves also t ell us something else:
that the pump will deliver the flow
rate and head press ure shown on the curve. In the example we have cited, we selected a 200 mm [8 in] impeller whi ch will deliver head presure of 600 kPa at a flow rate of 40 m '/hr [head pl'ess ure of 87 psi at a flow rate of 175 gpm] . Suppose when we sta rt to o"perate the pump that we r equire a head pressure of only 550 kPa [80 psi] at the design flow ra teo I f we look at tile 200 mm [8 in] diameter pump curve, at 500 kPa [80 psi ] the flow rate through the pump wi 11 be 56 m '/hr [ 25 0 gpm ]. In othel' words, the pump is goi ng to de li ver a flow rate and head pressure along its operating curve. Even though we do not need as much head pressure as it will deve lop, we cannot reduce the flow rate without increasing the head pressure. What th is means from an opera ti ng standpoint is thi s:
if a constant speed pump
develops more head pl'essure than we need, we must have a pressure reducing device on the pump discharge that wi ll take up t he excess head pressure that t he pump develops. Using a pressure reducing dev ice is wasting the energy t hat was used by the pump dr iver to put up the pressure drop we are taking across tile pressure reducing device.
We can save t hat wasted energy by installi ng a smaller impeller in the pump. Look at t he pump curves again.
At our operating flow rate of 40 m '/hr [175 gpm]
and
opera t ing head pressure 550 kPa [80 psi ], we need an impell er having a diameter of 195 mm [7-3/4 in]. We can purchase t his size impeller from the pump manufacturer.
When
we put the smaller diameter impeller in the pump, we will have a new curve shown in the
dotted lines of the pump curves. This is our new per formance curve. ru n the pump at our actual operating conditions wihtout wasting
It will allow us to
POW€ I'
in the driver.
We purchase the pump with a 200 mm [8 in] diameter impeller to give some excess capacity. The manufacturer suppli es us wi t h performanc.e curves for that pump as shown on the next pages. The top curve is the sa me as th'e 200 mm [ 8 in ] diameter impeller on Page 20 . It shows the pre ssure head at di fferent flo w rates. The maximum head pressure the pump will develop 650 kPa [9 3.5 psi]. the pump.
This head is developed with no flow through
In other words, if we turn the pump on and close the discharge valve, the
pressure gauge on the disch ar ge will read 65 0 kPa [ 93.5 psi] more than the suction pressure gauge.
If the occasi on should arise t hat we want to increase the flow rate
through this pump f rom 40 m '/hr to 60 m '/hr [175 gpm to 265 gpm developed by the pump will drop to 540 kPa [77.5 psi].
J,
the head pressure
22
PUMP EFFICIENCY It is important to rec-
ogni ze that a pump will oper-
.
-
ate at some ' press ure and
.;
SILNTS ...:..
'
' -I ~
>
•
flow rate on or near its operaling curve. stage
Large multi-
pumps
may
deviate
slightly from the operaIi ng curve. As a pump wears and
clearances increase, some in-
<
~ 600
~ ~
~
ternal leakage from the dis-
:
,.
-
.~
and
the
.....
.. _ . ·i
- .. --
-.. ~
.. ..;.
-,
,- _ . ' I
500
problems.
pump
We observe the
.....
head pressure and flow rate through the pump and compare
it
to
the
operating
"
'
.
60
. - . .;
- .'
!.,.
I
.
.. - - -... .., ,
,
-1
~
,
20 ,
is
,
10
- I..
-' --
,
••
,
:
-J.
,
o
F.
_.
"
'" .-
t ;" .
,- .-
..
- ",.-
..:
I
,
:
-"
,
.."'
1 T
:
.-
; , i
-
-
.0
~-
.,.
-..,
".
-
o
Pump Efficiency Centrifugal pumps are
'
".
~ 500~
f
'i
.. .;:. = .1 : ~ 400~ B .. . , .,
·
. ,
10
~
"
" '- a
.; .:. I .;
, ,
• r -•.
~-.
.-
.....
"
,-
, i
.!. .
20
40
o
~
' " •
OO:J
.... "f
60
Pl..M' CAPACITY. M J I'rfl
PERFORMANCE CURVES FOR PUMP WITH ioo MM IMPEl.LER AT }500 RPM
not high effi ciency energy transfer devices.
In other
wordS, only part of the energy used by the driver is actually transferred by the pump into pressure. The pump efficiency is the percentage of energy that transfers from the driver to the liquid in the form of presure.
~
-,
1"- -
I -.
energy
driving the pump.
,
I.
Otherwise,
wast ing
".
..
:- ,- ..
- .....
t _ .
are
•,:
-
the curve, it may be time to we
oj
i -!
.. ;. , ..
. .,..,
curve. If it is too far below repair the pump.
- : .- - -
- "- '... ' ....
~
~ K
..
'-
.
2
' r- .
I
,
.,.- ..,
.
T--
•"
·
_
POINT
line parallel wit h the original troubleshoot ing
"
~
_.
opera ting
This is a way of
....
.! .
curve moves downward to a
curve.
·
; - DESIGN '
550
charge back to the suction occurs,
"_1
- .. . .
~ .
"
,
.
-
,
"
The efficiency cu rve for the pump we selec ted
indicates the maximum efficiency for this particular pu mp is about 63%.
PUMP EFFICIENCY
23 ecuSHl.NTS
This is the highest efficiency we can get for th is pump.
At our design flow
rate of 40 m 3/ hr [175 gpm 1, the pump efficiency is about 61%. The efficiency drops off
-
,-
,
~
i ~
t
.~
•
-r "DESICN - POINT
80
-
I.
_._
-. ,
,
rapidly as the flow rate reduces.
70
. -. -.
60
.-t-r-
The ene rgy supplied by the driver which does not
- -
..
,- -,-
transfer into pressure energy
r
, I
,-
inside the pump has to go somewhere.
Part of it goes
,-
.:.. 40
to friction; part of it makes up for internal leakage; the
-,
remainder enters the liquid in the pump in the form of heat. As long as the pu mp is opera-
L
o
• 20 ~
"
ting at an effic iency of 30% or more, the heat energy that
-
•
~
_.
~--d-
•
(AD '
. SU ' ClIONt-i · _ . _ .. , \QllID
- .,
transfers from the driver to
10
Q
the liquid in the pump will cause only a degree or two rise in the liquid tempera-
o
'"
100
150
200
250
o 300
PUMP CAPACITY I GPM
PERHRMANCE CURVES FOR PUMP WITH B N::H IMPELLER AT J500 RPM
ture.
S ~
~
However, at low pumping rates, the efficiency may drop as low as 10-20%, which means that a larger percentage of the driver energy is entering liquid in the pump in the form of heat. In this situation, the temperature rise may be several degrees, which may vaporize part of the liquid or expand the internal parts of the pump to the point that damage may occur.
Problem 4 What is the head pressure and efficiency at a flow ra te of 50 m 3/ hr (220 gpm J?
§
DRIVER POWER
24
A pump having several impellers will have a temperature rise ac,'oss each impeller. In some instances, this limits the number of impellers tha-t can be installed in a pump
case.
65.
G. Driver Power The
power required
to drive the pump is indica ted on the curve. power
increases
as
flow rate increases.
The the The
51 LNT5
, <
•~
.
~'
- ,
~
,
"
of
,~
>0. ..
;
1
. ,
,
.. ,
I.",,,
'. • . -. !-.
r . . , . . . . r
20
-
." '
;-
1
, ,
1
.~
·, · • r
operating at a higher flow rate, we size the driver for
,
• -!
.
,
I
~(.p.
'"
~\\ltfI. 90 ...
,
'! I
•
.
,
.
_
pump perform-
,
,
.,...
1·;; · ·. _ ' -' •
•
10
.
The same pump with
'"
•
t
.
-,
•
t
, ."
,~.
... _..
-
,
,
,,
t
I "T" .j .
-.
I . 1 ..
"-
,
20 PUMPCAPAOrv,
a com mon motor speed.
--
.
,
I
..... __ ..... ..,. • 40 '"
,. -,
I
I -
. ~, .r-110l'1 H(.AO
UQUID~ "
1'
-
•
r-
.•
' •
.
"
.. . . . . , . . .; • • I ~,---"
ance curves are fot' a pump
This is
~
- ,
hp J motor.
per minutes (rpm).
-
•
.-
L ~ ,"
'
.
•
f. -,
• __ •
." l
.
•
flow rate,
speed of 3500 revolutions
•
.... .,..".
"-,"
the pump is capable of
The
I
"
-I"
which requires a 14 kW [20
"
,
m' / hr [175 gpm J is 12 kW
the maximum
,
,
40
However, since
• .
,.
,
[16 hp J.
-,
I.
'1,
'
,
rate
-
...
,
In this particular
flow
. I'
,
case, the power required at design
. j.
DESIGN POINT .. . -,
T ' -'
pump.
--
, .. -
power curve is used for se-
l ect ing the driver for the
!
I
~,.,
"
55. "
,
'
1-ti:4D"~' . ~E"Ssr....
-
600
,J
~~
,
"
40
"'-/Hit
"
PERFORMANCE CURVES FOR PUMP WITH 200 MM IMPELLER AT }500 RPM
a different speed motor (or speed control) would have a different set of performance curves. If we have a centrifugal pump driven with a variable speed .engine or turbine, it will have pel'formance curves at
each different speed. The effect of speed on the head pressure developed by the pump is a square l'OOt function. Cut the speed in half and the head pressure developed will be one fourth the original.
LIQ UID SUCTION HEAD
25
H. Liquid Suction Head
The impeller on a centrifugal pump pulls liquid into it from the suct ion line t o the pump. Liquid moves at a high velocity from the point that it enters the pump to the eye of the impeller.
This dis-
tance may be on ly a fe w em
signi ficant pressul'e drop inside the pu mp. This pressure drop that occurs within th e pump can cause some of the liquid t o vapor ize in the sucti on chamber of t he pump.
•
When this occurs, t he pump
i
will ""vitate or vapor leek. We
norma lly
prevent
locating the pump far enough below
the
vessel
we
pumping out of, so that the pressure
head
due
to
the
~
l ~
height of the liquid in the ~ vessel is mor e t han the pressure dl'op inside the pu mp and connecting piping. The pressure drop inside the pump i s expressed as height of liquid required at the suction line to t he pump.
P\..Np CAPACITY, GPM
It will var y
with flow to the pump as
PERFORMANCE CURVES FOR PUMP WITH 8 INCH IMPELLER AT J500 RPM
shown by the cur ves. The liquid sucti on head represents a pressure drop as liquid Dows from the pump inlet flange to the impeller.
We norm ally add about 10%to the liquid head to allow for
pressure drop in piping between the vessel we are pumping out of and the pump. In other words, the height of the liquid in the vessel above the pump will be 110%of the height
26
UQUID SUCTION HEAD
LIQUID SUCTION HEAD
r-F~~~~~~D I SC H ARGE ~~~~ LIQUID t.:::::.::> PUMP
shown on the suction head curve, If the pump is loca ted some dista nce from the tank or vessel it is pumpi ng out of, we will calculate the press ure drop in the piping and add it to the liquid suct ion head to ge t the to ta l pressure drop, and then adjus t the level in our separa tor so that we have enough liquid head p,'ess ure to ove,'come press ure drop in the piping and in the pump, If we allow the leve l to drop below this point, vapor will form in the pump and it will cavi tate a" vapor lock, Since piping pressure drop depends on size, it is importan t tha t the suction line be la"ge enough, [n cases whe re adj ustm ents in level cannot prevent cavitat ion, a larger suction line may be needed, Example
At a {low ra te of 40 m ' /hr [ 175 gpm], the suction head required at the pump is 340 c m [ 11 feet],
We determin e t he pressure d,'op in the piping
between the seporator and the pump is 100 cm [ 3,3 fee t], This must be added
to the head taken f rom the curve in orde,' to get the total heigh t of liquid above the suction to the pump, When the two are added, we get
Q
liquid head
requirement of 440 cm [ 14,3 ftl. If the level in the separat or fall s below this
paint, the pump will vapor lock and stop pumping , suction line is not completely open, it can cause
Q
If a valve in the pump pressure drop which will
reduce the suction head to the pump to the point that vapor lock will occur,
The suct ion head is referred to as NPSH by engineers, an abbreviation fo r Net Positive Suct ion Head, It is particularly important when pumping volat ile liquids, such as ethane, propane, or unstabi lized crude Oil; or if the pump is loca ted so me distance from t he vessel con ta ining liquid, On offsho,'e producti on pla tforms, crude o il pipeline pu mps often are located some distance fro m the separa tors or tanks, A booster pump is often
THRUST
27
used to pump liquid from the separa t or into the pipeline pumps.
The purpose of the
booster pump is simply to maintain suction head to the pipeline pumps so they will not vapot· l ock. Pump cavitation and vapor lock are major operating problems of centri f ugal pumps. As we mentioned earlier, when a pump vapor locks it simply stops pumping liquid. pump will continue to run.
The
If the problem is not co,·,·ected, the pump will overhea t
because no liquid is circulati ng through it to cool it. In this case, the pump is transfe,,·ing some of the energy from the driver in the form of heat, because no liquid is flow ing through the pump to remo ve energy in t he form of pressure. The im por t ant thing to remember about suction head is that it increases as the flow rate inc,·cases through the pu mp. Suppose we are operating the pump with the . curves shown on pages 24 and 25. It was sized f or a flow r at e of 40 m J Ihr [175 gpm]. The sucti on head required is 340 cm [ 11 ft J. If the fiow rate to the pump increases to 60 m J Ihr [ 265 gpm
J,
the liquid suct ion
head must be 585 cm [19.2 ft J or the pump will cavitate. If we design the elevation of our separator for a 340 cm [ Jl ft J suction head, we will not abe able to opera t e the pump above 40 m J Ihr [17 5 gpm
J unless we raise th e level of liquid in our separator. Remember
that the suction head is the pressure drop inside the pump, and we must add about 10%t o it to allow for presure drop in piping bet ween th e separa tor and the pum p.
Problem 5 Wha t liquid suction head is required at 50 m J Ihr [ 22 0 gpm J?
t
I. Thrust As a pump impeller rotates, a thrust force
SUCT ION ....-.
I
PRESStJRt.
develops which is transm itted through the pump fLOW
The
for ce
developed
in si ngl e impeller
pumps i s relatively low, and can be overcome with
. , . PRESSURE
I
shaft. The force is similar to that of an airplane prope ller which pulls the airplane through the air.
.... OISCHARCE
...
/
SHAFT
+ DIRECTION
Of THRUST
th,·ust bearings locat ed on the pump shaft as shown in the pho t ograph on Page 3. SINCLE It.flEl...LER EXER 15
n . fUJST TOWARD !iJCTD-I EN)
28
THRUST
j
t
Thrust forces in multistage pumps are compounded at each impeller.
Special design considera-
tions are required to contain these
forces.
One way of neutralizing
two forces is to install some of the impellers in opposite direction to others, so the thrust forces equal-
FLOW
SHAFT
+ DIRECTION Of THRUST
DIRECTION Of'THHUST
ize one another. This design does not totally balance thrust forces,
Tl-RUST NElJlRAUZED WITH OPPOSING IMPELLERS
but it red uces them enough so that small thrust bear ings can be used.
Some multi- stage pumps have all impellers facing the same direction.
This
arrangement results in the maximum thrust force. It can be neutralized by installing a balance piston on the high pressure end of the shaft. Pump discharge pressure is imposed on one face of the piston. A small amount of discharge liquid leaks around the piston to the outer face, and flows to the suction of the pump. This results in a press ure on the outer face of the piston of suction pressure. The force exerted on the inner side of the piston will equal discharge pressure times the area. The piston is sized so that the net force resulting from the piston is approximately equal to, and in the opposite direction of, thrust force from the impellers. This arrangement minimizes the size of thrust bearings required. Selection of a multi-stage untt having opposed impellers, or having in-line impellers SUCTION
DISCHARCE , - -BALA>CE
PISTON
-THllUST BEAR..,
7 STADE PUMP WITH BAlAf'CE PISTON
29
PUMP CURVE APPLICATION
with a balance piston, depends upon the pump service and the cost of the two un its. The balance piston is att ached to the pump shaft and rotat es in the casing. The clearance between the piston and the casing must be very low to prevent excessive discharge liquid from leaking around the piston. This requires a clean liquid inside the pump so that dirt does not get between the blance piston and the casing and wear one or the other parts. Multi-stage pumps having opposed impell ers require spec ial passageways through the casing for liquid to flow from the fi nal stage of the first se t of impellers to the first stage of t he opposing se t of impellers. This adds considerable cost to t he casing.
J. Pump Curve Applicati on Now let us app ly what we have learned to an operating situation. Liquid from a sevarator must be pumped into a st abilizer. Operating conditions of pressure and flow are as shown below. The pump selected for this service has performance curves as shown on the following pages. The basic design point is for a flow rate of 68 m 3/hr [300 gpm J and a head pressure of 345 kPa [50 psi J. At these conditions the pump efficiency is 73%, and the dr iver requires a horsepower of 12 kW [ 16 hpj. A 15 kW [20 hpj motor was provided wi th the pump.
1 ]O}~ kPa [1$0 p1i]
-
690 kPa [100 kP~
STABIUZER
",""p
DESIGN COI'VmONS FOR ST ABIllZER FEED PUMP
First of all, look at the power curves to deter mine what maximum continuous flow rate can be ma intained in the pu mp without overloading the motor. The maximum power required by the pump, is 15 .8 kw [21 hp J, which is 5%above the power of the motor. We can safely operate at 105% motor load for extended periods, so we can say that the motor does not Ii mit the flow t hrough the pu mp. \
Let's get back to the design point on our pump.
Checking the efficiency at the
PUMP CURVE APPLICATION
30 des ign
flow
rate
SI LNTS
of 68
m ' l hr [300 gpm I we find that it is 73% efficient at that point. This means that 73% of the electrici ty used
~ LoT
., "
300
~ ~
in driving the motor is con- ~ verted into pressure energy
'. ,, '
.. , 200
inside the pu mp. The other
,
leakage
in
,
,. ,,
,
the
"
80
•
,
27% is lost to frict ion, to internal
I '
,
, I
70
~~
,
t ,
pump, and to temperature
t
, .0
"
rise in the liquid. •
Refer to the suct ion the design flow ra te of 68 m ' l hr [3 00 gpm 1, a suction
f
head of 270 cm [9 ftl is
this
distance
above
the
I"
,.
means that the level in the separator must be at least
..
...
between the separator and
,
I,
'
..
,
,,
... , ,
t
I'
,
~
I
~
,
. •
I' I
lJ(JJ\O
I'
, i 20
.. .-....Il-IE,o.O •
SUC1\U"
'0
.
.,
60
..l-
<
.. I
I , ...
i ..
r
"
,
, 80
'00 3
,
, .... !
I
o
,,
t - t • -
pump. We normally add 10% for pressure drop in piping
I
t
. '
I
,
,
f
.~~
ck:\...j~""
,
, ,, ,
- . , , ' .. iJ' • 4
required at the pump. This
.,
.,
head curve. It shows that at
I ..
100
,
oo~
300~
.,
,. 200 120
the pump, so the level in the separator must be 297 cm
PERFCRMANCE CURVES FCR STABlllZER FEED PUMP 51 UNTS
[ 9.9 ft I above the pump. Look at the suction head curve at a flow rate of 114 m 'lhr [500 gpm I. It shows that the liquid head to the pump 'must be at least 455 cm [15 ft). If we add 10% for pressure drop in piping to the pump, we get a height of about 50 0 cm [16.5 ft I. Suppose the maximum level we can maintain in the separator is 455 cm [15 ft I above the pump. We deduct 10%to allow for pressure drop in piping, which leaves 410 cm [13.5 ft I of suction head. At this height the maximum flow rate the pump will deliver
PUMP CURVE APPLICATION
31
OGJSH \..NITS
without vapor locking is about 108 m3/ hr [470 gpm). Assume we learn that the flow
to
the
separator and
,,
through the pump will increase to 102 m 3/hr [450 gpm J. Also assume that the pump discharge pressure must be 1035 kPa [ 150 psi)
in order to pump liquid
•
into the stabilizer.
!
Refer to the head curve at 102 m 3/hr [450 gpm) : the pump will deliver a head presSure of 300 kPa [43 psi). If we
,
deduct this from the discharge pressure, we get a suction presSure of 737 kPa [107 psi ). This is the pressure we will have to
t
hold on the separator at a flow rate of 102 m 3/hr [450 gpm). Now look at the liquid suction head curve at 102 m 3/hr [450 gpm). It shows that the level of liquid must be at least 380 cm [12.5 ft) above the pu mp. Adding 10%for safety gives us a
400 PUMP CAPACITY. GPM
PERIU~MAt«.:E
CURVES FOR STABIUZER FEED PUNP ENGUSH LNlTS
total liquid height of 418 cm [13.75 ft J. We will have to raise the level in the separator to this height above the pump,
and hold the separator pressure at 735 kPa [107 psi) in order for the pump to deliver 102 m 3/ hr [45 gpm) at a discharge pressure of 1034 kPa [150 psi). Suppose the pump has been in service for a few years, and we are checking its capacity against the design curve. We have a flow meter in the line which shows 79 .5 m 3/ hr [350 gpm J. Pressure gauge at the pump discharge reads 1035 kPa [ 150 psi),
"
,.
-,'>',
3Q.' ~pd . ~
a. <", .
_t
" p'.~~~~ .
.• -.,.
.,~;.. :
StiC:U0~ " ,,_ .
·ga).!ge
"-' . ' ~~.~,
line
. ,',.. '"" J.~;
•. .. _ ~
"
,'.
' ~eads
.: 'I
~
' j ;'
,.' ·' 3:~ I<:Pa[; lO§', p~i'l.' Ttw ' 'Id i((are"~, onhe t.wl) is
~
.r. :: • ..., ,; '
J'.
,3,Hi kPa [45 psi j whi"h
~
. : , J '-.'
.
'" ,
; is.. th'~, head 'we~ure put ,
',up,,by: th¢:'pump.
,
'We, ta'k,r this",ilatli
.'
,m'/1ir and ~!'o . ... . . ". ..... k:~a hea,d p,ressur~ [,35'0
" - "',19,:'5 r, ". ,
.. .
gpm and .45 psi: head
"
11i~sspi:
.
, com -
", . ',.
~~e ,p~r ~,
':p,are :.-it, wiW
"'f-ot:rn'arr<:e 'CJirv'e for' our
fu
, 7:9.5
3
/h r
__
.
'~ "
' l>u~p" We find ' fliat at 1
--~~:-:~'r~ . J'
•
[35,OgPTQ \;
the"l'!~mp' shbuld "delivllF
:I:F~ '~ '.,
~
(0
~"'. ffi
':'
" ',
.,'
,ihe
.
.. .I ha~.," .. i ncr'eased "'" .•..
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j.
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,
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.
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.
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.;
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-
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.. ... J•• ~-
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.
..
':.
~:: . -.!~.
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-....:- ~!.~.:' ...~ - '1- r".1; l'
' ,•
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:. _.. ,.'.!,.:..
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i:
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-
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)
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.:..
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,
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_I ,- ':lQ'O r""L , .~ ,
,l
~'. : " '- "'; T:~ " ;,' ~lQ0\iJ.~· " ' :, ", .": ,.. ' - ~... -~ .-' I , " 1 ~ . '."H :: ', . ,~ ' ..• .. :.r.' 1 ; ' ., ''- ,> -~. - , ' : I - I T
.. ' I ' ,-::,
clear-
J"
.
- f '" • I ,
o
'~ii'm~
·':.-r",., ..
J
,
.. ,
" ,':
,~h~t : t:~e i,;;pell~r ha~, anMs :jnsi
,
··f ",
t·: . _. ,IL .... .",' ! L. '~:"'r"" ,.,-" ;:t:::ti±' ..,--
',QnIysfj,ii is. lik,elii ,w
--,
, ,;- , \ -':.;.- •.'-0 ' "
0" 5
,
' I
.': .•, :.,p
. J , c;.;'::ic~ , ljlfgj ·.· ,r-r:·:_.: :~.. I · , ' :'? ~~."ij __ ".' . . . ~," ,~~;, ;i:,:, ..,' ; .. "1 : :~ ;SO~!~ :"':' ,:; - ~- I' :-I" ", . ;" :..,'. .
'i
33-5 kP'a [48:~p's, i j of , h~ad pres.sure, .., S;rice " , ... . ' . " ii
~, :- , . ;~
'~ ' r:-"l';
:
. , 't
20,
j
I
,
;
!
6IJ
-10 :
l
- SO
' _I
.,
,200 12,2 '
1;,00:
"
due:..,fo,
": wea!i, •
as,the; pu'mij iii,1I conlinue to' de!l~ertlji : liquid wtlich '~~cU:iriulaies , in the" " := ',. ~ ~eparator''',1,i pnopab;i¥,is [l~ '~1:~.~NY i'o r~t>hc, it, at'}"i~; t\~e. ,\Ic>wmr, we!stlQu1(1. .p1te.\!~ " . ',,
As
long
1
'.
-.,.'
.. ,
.....
-
-
.,
' ';' ';
>
'
••
"
,
,.
', '
,
'fhe p,eriorll)a;r:tee ;per)pdjf1!t1,ly.,jn: 6I;lI"t to see 'if .J he ,condition' g,grs woi'st;, ' Qyr,le·~, " T.
,~"
J"
.•..
'
" " . ,
~
,freque~tly" onc~ .wea.r!kgtns: ,!t a~~~Le.~al~f r!!pidly:,,1'~~ e;((eet 'if, !~j,S iS I~, reduG~, i~,~:\:>;~ ;'~ea~l p.t~~.~re :t~e,;~4m-p ~ii}~:-~~~'i~~~~; :~"~f :, Each centrifugal :discussed. ~
'b~mp
"
has
'p",,'{9rm~nce
~
, •
,,",r,ves 'sjm ilar to the .. 'o~s we:'Jilive'
OJ1r,ves;, Pr\)v,td,i d," ~y. ;,the; have fi.~9.w.n ,is \~ ~ i~e h~?,a pr.~~ui~ "'~~" I11~A~f;;,:q~Uj:~,i~ , ,
The only differeli'ee b'etw,fen 'ihe pe'rforman'c e
'!l'ariufit~turei' . arid itlo~e
,we
•
t,
,r
". .
, '
PUMP CURVE APPLICATION
33
performance curve is given in meters [ feet J of liquid rather than kPa [psi J. The he ight of liquid is conver ted to pressure by the following equations: SI UNITS, kPa
ENGLISH UNITS, PSI
LIQUID HEAD PRESSURE = (Height,m) (Rei Dens) x 9.8 = (Height,ft) (Rei Dens) x 0.43 The term relative density used in the head pressure equation is the new term in Sl nomenclature
that replaces the
traditional term specific gravity.
the same thing and are found by
LNJTS
dividing the density of liquid by the
:
density
of
water
at
the
,I
Both mean I
I
same
~
conditions. The performance of each pu mp should be checked at 3 to 6 month
~ ~
intervals to see if the pump is opera- ~ ting near its curve.
When the head
pressure drops below the curve, performances should be checked more
•
frequently so that the point at which
I
the pump will fail to deliver the required flow rate can be ant icipated and repairs made before this occurs. In checking the suction and discharge pressures of the pump, it is
~
best to use the same pressure gauge,
ffi
or use two gauges that have been
•~
~ gauge is preferred as it will give 5 recently calibrated. Use of th e same more accurate readings. Our primary concern is that of pressure difference and not the actua l pressure readings. Two different gauges may each be slightly
in
error
so
that
the
difference in readings of the gauges will not be accura teo
300 P\..Jt.ofI CAPACITY, GPM
400
PERfeRMANCE CLRVES FeR Sf ABIUZER FEED PUMP
EU;USHLNTS
PUMP CURVE APPLI CATION
34
Another use of the performance curves is that of estimating the fl ow ra t e through a pump.
This can be done vel'y easily by measuring the curr ent and voltage to a motor
dr iven pump . Power equations for 3-phase alternating current motors are: MOTOR POWER:
KW = Volts x Amps x 0.00l5
HP = Volts x Amps x 0.002
Example The st abiliz er (eed pump with curves shown on pages 32 and 33 is driven
with an AC motor that has 440 volts and 20 amps. Calculate the Power and (low rate through the pump.
SI UNITS POWel' Equa tion
Volts x Amps
ENG LISH UNITS
x 0.0015
x A mps x 0.002
Volts
Motor s volts
440
440
Motor amps
20
20
Substitute in equation
= 13.2 kW
440
x 20 x 0.0015
440
x 20 x 0.0002
= 17.6 hP
From pump curve, jlow rate at above power
76 m '/hr
335 gpm
Problem 6 Refer to the stabilizer feed pu mp curves on Pages 32 and 33 and answer the following:
A.
Flow rate is 80 m' Ihr [ 350 gpm )
C.
We are checking the per formance of
Head pressure is
t he pump after 2 years of operation.
Effi ciency is
Flow Rat e: 75 m' Ihr [330 gpm )
Dr iver power is
Discharge Pressure: 1070 kPa [155 psi)
Liquid Suction Head is
Suction Pressure : 740 kPa [107 psi J Head Pressure is Flow ra te should be _ __
B.
The current to the driver is 10.6
D.
We are
having difficulty with the
amps and voltage is 660 v.
pump
Driver power is
gOm '/hr. [400 gpm J
Fl ow rat e is
Height of liquid in separat or must be
Head pressur e is
vapor
locking
at
flow
of
ID. OPERATION
35
A. Start-Up Procedure 1.
Check for bearing lubrication - observe oil level In bearing housing or other
form of lubrication. 2.
Open valves in the suction piping between the pump and the vessel containing
liquid to be pumped. 3.
If the pump is to be started with no pressure at the discharge side, close the
discharge valve.
If there is normal pressure on the discharge side of the pump, the
dischal'ge valv e can be left open during start -up if a check valve is included in the discharge piping. 4.
Vent vapol's from the pump casing until a continuous liquid str eam nows from
the vent valve. 5.
Start the motor or d,·iver.
s,~"
?
SUCTION
drlwer
Is";J o
TA
'
,
Open
jI,
"'Ilve III p.plng.
IUCt U)rl
~
Open ... ent .... 1". U'llil t tuOy strum
of liquid come. ouL Then clo-e
11-_
,
:
Cibtetyt dllcn,rge pre.ure. II it i. 7
... eper locked.. Shutoown end repel! Slep II.
,. r
NfTlC .. '\oICUOIl j)l1!aute, PUI'l'll ".,
1 r-~lV=(~N='~~==~~~==~ DISCHARCE J
"there ill pl1! .. ure In db· chMge pipifl9, open '1.1" ..
DRAIN
(0 Cheek lor bearing
V
oV
Check lor nol.e or IIlb,.lIoo. Shutdown If either i, noted.
l
LOW FLOW RECYCLE 6.
Observe the pu mp for unusua l noise or vibration.
If either occ urs, shut down
the pump immediately. 7.
Observe the pressUl'e gauge on the discharge side of the pu mp. If it is below
normal, the pump has probably vapor locked. Shut it down and repeat Step No.4. 8.
It is not unusual fOi' a pump seal to leak some when a pump starts, particularly
if it is a new seal. Leakage should top within a few minutes. If a pump has been sitting in the sun before it is started, its temperature may be
CONTROL OF PUMP FLOW RATE
36
above that of the liquid being pumped.
As soon as the liquid enters the pump, its
temperature rises and so me liquid fl ashes. The pump will immediately vapor lock when vapors are present in it. Consequently, it will be necessary to vent the pump until the liquid from the vessel has cooled the pump to the same tempera tul'e as that of the liquid. B. Control of Pump Flow Rate The pump curves we discussed in the prev ious section applied to pumps operating at a constant speed. The flo w ra te through the pump is determined by the pressure head developed by the pump.
A control valve in the pump discharge line is often used to
control the flow I'ate through the pump. One such type of flow control is shown below.
rr===* GAS PRESSURE CeNTROl
"")INloj)(:.iiiiiiiioi)<.•• DISCKARGE LIQUID lEVEL CONTROL VALVE
FLOW CONTROL USIt-13 CONTROL VALVE IN DISCHARGE LINE REGULA TED WITH LEVEL CONTROLLER
In the above drawing, liquid is pumped out of a separator which has a stream of liquid and gas entering it, Gas flow leaving the top of the vessel is regulated with a pressure control system that holds a constant p,'essure on the separator. Liquid is pu mped out of the vessel to its final destination. A level control system regulates the flow rate through the pump. A level controller mounted on the separator senses the level inside the vessel.
[f
the level rises, the controller signals the level
control valve to open. This lowers t he pump discharge pressure and also lowers the head
37
CONT ROL OF PUMP FLOW RATE
pressu re developed by the pump. The effect is to incr ease the flow I'ate t hrough the pump because the head pressure was lowel·ed. Conversely, if the level in the separator falls, t he level controller will signal t he control valve to close. This increases the pump discharge pressure, and the head pressure, which reduces the flow through t he pump. Another typ e of flow control through a pump is shown below. A pressure con troller on the discharge line of the pump is used to I'egula te the flow of liquid pu mped from th e storage tank. This type of con trol is used on L ACT units. The pressure controller is set at the desired discharge pressure, and it signals a cont rol valve to open or close as r equired to maintain a const ant discharge pressure. If the pressure rises, t he contr oller will signal the con tl'ol valv e to open, which lowers the pressure (and head pressur e) and i ncreases flow t hrough th e pump, and vice versa.
PRESSURE CONTROLLER
' 1::;;;~ OISCHARG E LIQUID PRESSUR E CONTROL VALVE ;><.
STOR AGE T Ai'»<
FLOW CONTROL WITH CONTRQ VALVE IN DISCHARGE LINE REGUlATED WITH PRESSlRE CONTROLLER Use of a contro l val ve in the pump discharge line to regulate flow through the pump is undesirable for t wo reasons:
1.
The control valv e has a pressure drop across it, which represents a wast e of energy used by the pump dr iv er.
2.
PI'ocess conditions regulati ng the control val ve in the pump dischar ge line may be such tha t at ti mes the pump operates at a fracti on of i ts design flow ra teo
In t he sec ond situat ion, t he pump efficiency at low fl ow rat e may be 10-20%, and so me of the lost dr ivel' energy enters the liquid in t he pump in t he for m of heat. Hea ti ng liqui d in the pump may cau se some of it to boil and for m vapor, which wi ll result in a vapor lock conditon. Heat may also expand th e impeller so that i t I'ubs aga inst th e casi ng \
and damages the pump.
LOW FLOW REC YCLE
38
FLOW Se t at 20%
/d'''i ~ln flo w ra te
t
Flow in is 15% design.
UUI.le l
~- IIIm111I1i:~lIIIIIammdm.lIIIII. OUTLET PUMP FLOW METER
15% of design fl ow.
PUMP Flow meter signals flow controller that flow rate is 15%. Flow controUer senses flow ra te is less than its set point (20%) and signals the con tro l valve in recycle line to open enough to le t 5~ fl ow through it. Flow through pump is now 20%; 15% goes to outlet and 5% flows in re cycle.
LOW FLOW RECYCLE Heat build-up at low flow ra te is prevent ed by means of a low-flow recyc le system. A flow meter installed on the pump discharge line measures t he flow rate out of the pump and sends a measurement signal to a fl ow cont roller.
The flow controller is set to
maintain enough flow to the pump so that no damage will occur from high temperat ul·e. Flow rate is usuall y set at 15- 20%of the design flow of the pu mp. If the fl ow out of the pump is less than the flow ra te set in the flow controll er, t he controUer will ope n a control valve in the bypass line, so that t he flow rate through the pump is never less t han the set point on the flow controller (15-20%of t he des ign flow rate). Use of a con tro l va lve to regulate flow through a pump, whethe r it be a low-flow recycle line or in the pump discharge line, resul ts in a waste of energy supplied by th e pum p dri ver.
Most of this energy waste can be elim ina ted by using speed to con trol t he
flow rate through the pump. The speed is increased to raise the flow and vice verSa . [f the pump is dr iven by an engine or t urbine, the speed ca n be changed by adjust ing the governor on the dr iver. Speed Changes can be made by hand, or an automatic sys tem similar to that sho wn on the next page can be used. [n t hc system shown opposite, a level cont roller moun ted on the se parator senses the level inside tha separator.
If the level rises, the controller signals the governor to
increase the speed of the driver, and vice versa.
Var iable speed electric motors are becoming more popular in t he oilfield as the cost
39
CONTROL OF PUMP FLOW RATE
PRESSURE CONTROLLER "T""
LEVEL CONTROLLER INLET STREAM
SEPARATOR
iII!li!i!ll.~!>
GOVERNOR OR ENGINE DRIVER SPEED CONTROL SYSTEM USED TO CONTROL F LOW THROUGH PUMP of energy has ('isen in recenl years.
The speed of direct current (DC) motors can be
varied by changing the voltag e across the motor, Alternating current (AC) motor speed is changed by regulating lhe frequency of the current. Motor speed change can be done by hand, or it can be automatic by using a proccss controller to change the motor speed
controller. The effect of changing pump speed on the capacity, head p,'essure, and driver power is shown on the graph on the next page, Suppose we wanted to operate at a flow of 80%of design, but we want to maintain pressUl'e head at 100%, We locate the point on t he graph at 80%capacity and 100%hcad, and find that a speed of about 98,5%of design will provide the flow rate and head pl'essure required. This is a speed reduction of only 1.5%, which would appear to have a minot' effect on the energy consumed by the driver. The energy consumed by the driver is a function of the capacity multiplied by the pressure head, In this case, lhe power consumption is (80%capacity) x (100%pressure head)
= 80%of design power, If we operate at 100%speed and 80%capacity, the pressure head
40
SHUT DOWN PROCEDURE ,
, .. .; -. 1
100
,
,-
-
t
,
t
t
80\ CAPACITY
i
· lO()\ HEAD 98.)\SPE[D
~ POWE~
•
,,
I
- "r
i:t.. 1-100\ f..i.. DESKiN POINT HEAO
.
-
._ 100\ CAPACITY
!!.
" -,
l
,
I lllOl poweR
'901i:
•-, c, ,Hi r:
,I-.
Sf)tCQ
~ 80
-:
!1O' C APACITY :
~ e Q
-,
73\ POWER
- -,
- "
~
w
., ,-
i . 81\ HEAD
~ 0
•·
r.!.1
70
,
i
r
60
~
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t-
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64' HEAD
I I
)1\ POWER
,I
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.
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,
,
20
'0
60 F\.IMP CAPACITY
-
T
'I'
o
" '
~ r-r' ~(O
-, ' ttittf:tt±tJj~ 80\ CAPACITY
t
t·
'
100
80
I' fT
o
OESCH
EFFECT CF PUMP SPEED ON CAPACITY, HEAD PRESSURE AND DRIVER POWER
would be 103%. Power consumption would equal (80% capacity) x (103% pressure head) 82.4%of design.
=
The net effect of reducing speed is to save 2.4% of the design power of
the d"iver, The cost of driver energy is about $200 per year for each kW [$155 per hp J consumed, whether it be fuel to an engine or turbine, or electri city to a motol',
A small
reduction in power con sumption by severa l pumps in a process facility will result in a
SUbstantial reduction in energy costs. C. Shutdown Procedure J,
Tum off the pump motor.
2_
If the pump is to be depressured for maintenance, close valves in the suction and discharge pipi ng,
drai n valve.
Open the vent valve, and after depressuring, open the
,
ROUTINE OPERATING CHECKS
41
D. Routine Operating Checks
1.
Check the pump for unusual noise or vibration.
2.
Check the level of oil in the bearings and add addit ional oil if necessary.
3.
Observe the packing or seal for leakage.
Report any leakage which is noted.
Shut down pump if leakage is severe. 4.
Fee l the bearing housings and pump case to see if they are hot.
5.
The performance of each centrifugal pump should be checked periodically and any decline should be corrected before it becomes serious. The performance of a pum? should be checked against t he pump curve at least once a month. Performance is checked as follows: a.
Observe the discharge pressure and suction pressure, and take the difference of the two to determine the head pressure ac ross the pump. Accurate gauges should be used for measuring at each point.
b.
Convert the head pressure into height of head. Use equation on Page 33.
c.
Determine the flow rate through the pump.
d.
Compare the pressure head and flow rate with· thet of the performance curve for the pump.
If the observed pressure head and flow rate are below the cu rve, the pump is not performing up to its design capability. Most process pumps are purchased with 10 to 20% excess capacity. Consequently a pump may be able to deliver flow and pressure required in the process even though it is operating below its design capability.
However, if its
perfor mance is checked monthly, and a gradual decline is noted, the point at which repairs will be necessary can be accurately predicted, and repairs scheduled to minimize the opera ting down time.
Problem 7 A.
Flow through a pump may be controlled with:
___ 1. Low flow recycle system. ___ 2. A control valve in the discharge line. _ _ 3. Regulating the speed of the pump.
42
TROUBLESHOOTING VAPOR LOCK B.
When a pu mp vapor locks, discharge pressure' is: ___ 1. Less than suct ion pressure. ___ 2. About the same as suction pressure.
___ 3. More than suc tion pressure.
C.
Low flow recycle prevents: _ _ _ 1. Overloadi ng the driver.
_ _ 2. High discharge pressure ___ 3. Temperature rise in the pump.
VI. TROUBLESHOOTING
A. Troubleshooting Vapor Lock When a pump vapor locks, its discharge pressure will be about the sa me as suction pressure .
The fo llowing table indica tes the usua l causes of cavitation and the procedure
for troubleshooting : Cil USE OF VAPOR LOCK 1. Low liquid level in vessel being
TROUBLESHOOTI NG PROCEDURE a. Raise Liquid Level
pumped out of. 2.
Low flow rate through pump.
a. Raise flow rate by re-cycling some discharge liquid back to pump suction.
3.
Valve in suction line is partially closed.
a. Check position of all valves in sucti on piping for
full
OPEN.
4.
Pump suction line obstructed with
a. Clean strainer on suction line
pieces of wood, di rt, slag, etc.
b. Disassemble
suction
pipi ng
and remove obstruction.
5.
Pump casing is hea ted from sun or
a. Insulate pump.
other source of heat which causes
b. Cover pump.
liquid inside pump to boil.
c. Cool pum p wi t h fan or water.
43
TROUBLESHOOTING LOW FLOW RATE
B. Troubleshooting Procedure for Low Flow Rate CAUSE OF LOW FLOW RATE 1.
Excessive pressure head. Discharge
TROUBLESHOOTING PROCEDURE a.
Measure pressure head (Discharge
pressure is above nor mal, or suction
press ure - suction pressure). If it
pressure is below normal.
is more tha n normal, determine if suct ion pressure is low or discharge press ure is high. b.
If discharge pressure is high, check discharge
piping
for
partially
closed valves. If control valve is in discharge piping, check to see tha t is is no t stuck in a partially closed position. c.
Check for pressure r ise in vessel or line that pump is pumping into.
d.
If suction pressure is low, check for low level in vessel pump is taking suct ion from .
2.
Impeller or casing has worn. Discharge
a.
Replace worn parts.
a.
Raise level
pressure will usually be less than normal.
3.
Pump is vapor locking.
in
vessel pump is
taking suction fro m. b.
Recycle some discharge liquid back to suction end if flow is less than 20%of design.
44
NOTES
45 CENTRIFUGAL
VALIDATION
SI UNITS
PUM PS
I.
Refer to the perfOl'mance curve A.
Flow inc"eases from 60 to 80
10 J /h r.
Discharge kW.
The level in the separa tor feeding the
em.
The mot or driving the pump has 3-phase AC power at 66 0 volts and t he current is I S amps. Motor power is _ _
D.
Suction pressu re is 700 kPa.
kPa, and power consump tion is
pump will have to be raised _ __ C.
- - -- - -
Page 32.
Flow Ihrough the pump is 60 m] / hr. pressure should be
B.
011
Trainee
kW . Pump now ,'a te is
- - m ]/hr.
Fl ow through t he pump is 70 m J / hr. The level in the separator feeding the pump is 25 0 em above t he pump. What will happen?
2.
List t he parts
011
the
pump show n.
3.
Th e purpose of a pump seal is _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
4.
All impeUer exerts a _ _ _ _ force parallel to thc pump shaft that must be ovel'come with a
or ncu tl'alized with a
--------
5.
A centrifugal pump raises liquid pressure by ______________ __
6.
Vapor lock "esults when _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ __ _ __
7.
Head pressurc equals _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
8.
The most economical way of controlling flow through a centrifugal pump is
46
SOLUTIONS TO PROBLEMS-81 UNITS
Type l.
2.
a
Process pump in gasoline plant
Vertical
Mechan ical
b
Water will pump
Submersible
Mechanical
-a
c
Pipeline pump
HorizontalMultistage
Mechanical
-e
d
Firewater
Can
Mechanical
-d f -
-b -c
=600 kPa
3.
1000 - 400
4.
575 kPa and 63.5%
5.
415 cm
6.
A. 335
E.
kPa
10.6 x 660 x 0.0015
=10.5 kW
=56 m 3/hr
74.5%
Flow
13.8 kw
Head P,·es = 358 kPa
300 cm C.
I 070 - 740 = 330 kPa m 3/ hr
84
D.
Liquid Suction Head at 90 m 3/hr
=
325 cm
+ 10%
33
L iquid Height in Separator
7.
Seal
A.
x
l.
x
2.
x
3.
B.
x
2
C.
-358 cm x
3
47 VALIDATION
CENTRIFUGAL
ENG LISH UNITS
PUMPS
1.
Trai nee _ _ _ _ _ _ __
Refc,' to the per'formance curve on Page 33 A.
Flow through the pump is 250 gpm. pressure should be
B.
psi, and power consumption is
hp.
ft.
The motor driving the pump has 3-phase AC power at 660 volts and the current i 15 amps. Motor powc,' is
D.
Di scharge
Flow inereascs from 25 0 to 300 gpm . The Icve l in the separator feedi ng the pump wil! have to be raised
C.
Suc t ion pressure is llO psi .
hp. Pump flow rate is
gpm .
Flow through the pump is 320 gpm. The Icvel in t he separa tor feedi ng the pump is 9 ft above the pump. What wi I! happen?
Z.
List the parts on the pump shown.
. ..
:,..
•
3.
The purpose of a pump seal is _ __ _ _ __ _ _ _ _ __ _ _ __ _ __
4.
An impeller exc,·ts a a _ __ overcome wi th a
.
force parall el to the pump shaft t ha t must be
or neutralized with a
---------------
5.
A centrifugal pump raises liquid pressure by _ __ _ _ _ _ _ _ _ _ _ _ __
6.
Vapor lock results when _ __ _ _ _ __ _ _ _ _ _ _ __ __ _ _ __
7.
Head pressure equals _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _
8.
The most econom ical way of controlling fl ow through a centrifugal pu mp is
SOLUTIONS TO PROBLEMS - ENGLJlH UNITS
48
1.
2.
!ype
Seal
a
Process pump in gasoline pl ant
Vertical
Mechan ical
r
b
Water will pump
Submersible
Mechanical
a
c
Pipeline pump
HorizontalMultistage
Mechanical
e
d
Firewater
Can
Mechanical
d
b
c 3.
145 - 58 = 87 psi
4.
84 psi and 63%
5.
13.5
6.
A. 48.7 psi
rt 8. Driver Power = 10.6 x 660 x 0.0002 = ~
74 .5%
Flow = 233 g~m
18.2 hp
Head Pres = 52 psi
9.7 rt C.
155-107 = 48 psi 368
D.
7.
A.
gpm
Liquid suction head at
10.8 rt
400 gpm =
Add 10%
1.1rt
Liquid height in separator
11.9 ft
x
l.
x
2.
x
3.
B.
x
2
C.
x
3
CE 'TRIFUGAL PUMPS
Section 1
An I ntrod udi 0 n to
Centrifugal Pumps
Centrifugal pumps are machines which use centrifugal force to move 1iquids.
I n Section 1 of Centrifugal Pumps , you will learn the principles, parts, and general operation of these pumps, what pump efficiency is, and how head and pressure are calculated. In Section 2, you will learn the details of construction of pump parts, including packing boxes, seals, bearings, balancing drums, and couplings. You will learn t he relation of alignment and misalignment to vibration, how pumps are lubricated, and how t hey are cooled in operation. In Section 3, you will learn the details of p ump operation: startup, normal operation, and shutdown. You will learn what the common problems of centrifugal pump operation are and how to spot and correct them. You win learn how to maintain the pumps fo r dependable, safe operation.
INSTRUCTIONS This is a programed learning course. Programed learJling gives information in a series of steps called frames . Each frame gives some information and asks you to make use of it.
Here is how it works. First, cover the response column at the right with a mask. Read this frame and use the information it gives to fill in the blank.
A micrometer is an instrument designed to measure in thousandths of an inch. A micrometer is a good tool fo r measuring very _ _ __ differences in size.
small
Move the mask down to uncover the word at the right of the f rame. If you have filled the blank with that word or a wor d that means the same, you are ready to go ahead to the next frame. The drawing of a micrometer provides information that will help you fill in the next blanks.
OBJECT TO BE MEASU R
• RATCHET
CAP
Seven major parts are shown in the drawing, but only the and the _ _ _ _ __ contact the object to be measured.
1
anvil; spindle
The next frame calls for a choice. Cir cle or underline the appropriate word. Of the two parts that contact the object, only the (anvil! spindle) moves. A program is a serie,s of fra mes that work like the ones you have just done:
Read the frame. Use the information to fill in the blanks or make a choice. Move the mask down and check the response column. Go on to the next frame. Remember to cover the response column with a mask before yo u begin each page. Now 1 go on to Page 3 and begin.
Notice th at the left-hand pages from here on are printed upside down. The program is designed so that you will go throu gh all the right-hand pages first , and then turn the book upside down and go through the othe r pages.
2
spindle
SECTION I AN INTRODUCTION TO CENTRIFUGAL PUMPS Exhibits I, 2, and 9 G're placed in the cente1' of the book 80 that they may be 1'emoved easily lor refe1'ence. Please 1'emove them now so that you. will have thent available when needed. 1. The force of gravity causes a liquid to flow from one elevation to a (higher /lmyer) elevation.
lower
2. Potential energy is st ored energy. Liquid at higher pressure has more potential ener gy than liquids at
lower pressure. Thus, liquid flows from _ _ _ _ _ _ pressure areas
to
pressure areas.
3. Liquid at highet' elevations has (1l1ol'e/ iess) potential energy than liquid at lower elevations.
higher lower mOTe
4. In the draw ings below, indicate the dir ection of flow with arrows.
A
8
)1
15 PSIG
30 PSIG
A
8
0 .... 0 3
5. 'W ithin a system, liquids flow because there is a pressure di!JfYI'ence in the system.
There (is/ is not) a pressure difference in this system.
is
6. Look at this system.
Since both ta nks have the same pressure, the liquid (flows/ does not flow).
7. A pump is a machine that adds _ __ __ _ to a liqu id.
does not flow pressure, or energy
8. A pump moves a liquid by mechanical means.
A
PUMP
B
By installing a pump in the plpmg between tank A and tank 'B, liquid can be moved from a ______ elevation to a elevation. 4
lower higher
9. Look at the drawing.
15 PSIG
30 PSIG
PUMP
A
B
This pump is moving liquid fr om a _ _ _ _ __ pressure area to a press ure a rea.
lower higher
10. Pumps are also used t o move 'more liquid in a given amount of time .
.. 50 GALLONS/ MINUTE
100 GALLONS / MINUTE
PUMP
The amount of liquid moving through th e pipe may be increased by installing a in the line.
pump
11. In moving a liquid f r om a lower elevat ion to a h igher elevation, the pump adds energy t o the liquid at low
elevation to provide the it to the high er elevation.
needed to lift
energy, or pressure
12. P umps are used to:
move liquids from ____ elevations to _ _ __ elevations ;
lower; higher
move liquids fTom _ _ _ _ _ _ pr essu re areas to areas of _ _ _ _ _ _ pressu re;
lower higher
incr ease the _ _ _ _ _ _ rate of a liquid.
flow
5
CENTRIFUGAL PUMPS 13. Pumping adds energy to a liquid. The energy of a liquid may be _ __ _ ___ by pn~lPing it.
increased
14. Cent1'ifugal force is the force of spinning.
-
When an object is spun arou nd in a circle, it pushes (outward from/ inward toward) the center of the circle.
outward from
15. One way to increase the energy of a liquid is to whirl the liquid around in ci rcles.
When a liquid is spun around, i t pushes (inward to the center/o~':1t\Vard
from the center) of the circle.
16. This outward force is cal1ed _ _ _ _ _ _ force. 6
outward from the center centrifugal
17. This is how a centrifugal pump works. Liquid first comes in at the center. It is then for ced _ _ _ _ _ _ from the center.
outward
18. Pressure at the pump outlet is great er than pressure at the inlet. Liquid leaving the pump has (more/ less ) energy than liquid entering the pump.
more
19. The pump part that spins the liq uid is called the impelier.
",'-A.,ING
--IMPELLER BL ADE
E (Suctio n)
Liqu id flows through the pump inlet and into the _ _ _ _ _ _ (center) of the impelier.
eye
20. The impeller whirls the liquid around in a ci rcle. The liquid is forced from the center to t he _ _ _ _ __ of the impelier. 21. The faster the impeller turns, the _ _ _ _ _ _ the liquid moves.
outside, or rim faster
22. The impeller is made up of guide vanes, or blades. The liquid's path is directed by these _ _ _ _ __
vanes, or blades
23. Centrifugal force pushes the liquid outward from the eye. It enters the _ _ _ _ _ _ when it leaves the outer edge of the impeller.
24 . 'Vhen the liquid enters the casing, its speed (increases/ decreases) . 7
casing, or honsi ng
decreases
25. Look at this impeller .
As the speed of the liquid decreases, its pressure
increases 26. As centrifugal force moves the liquid away from the
eye, a low-pressure area is formed (in the eye/ at the rim).
in the eye
27. The low-pressure area in the eye ca uses liquid to flow into the _ _ _ _ __
eye
28. ]11 t he centri fugal pump, liquid is moved by ce nt r ifuga l
force from a
to a
-pressure area at the eye
-press ure area at the pump's dis·
low
high
charge. For !'rame numbers 29 tlu'ouglL 51 look at Exhibit 1, which
shollJs a centrifitgal pump 'With all its pal'ts. 29. Find the impeller.
Energy is added to the liquid as it moves through the rotating vanes of the _ _ _ _ __
impelle r
30. The rotating _______ of the impeller move the liquid in a circular pnth.
vanes
31. The impeller is housed in the _ _ _ _ __
casing
32. Liquid enters the pump th rough the pump in let, or suction. It comes into t he center of the impeller through the impeller _ _ _ _ __
eye
33. When the liquid has moved to the outer rim of the
impellel', it enter;t peller to the
th~
casi ng and moves from the imnozzle.
8
discha r ge
34. As the liquid leaves the impeller, its velocity decreases. Velocity is par t ially conver ted to pressure in t h e cas ing. The liquid's velocity decr e~\ses, and part of this velocity shows up as an incr ease in _______
pressure
35. The impeller is rotated by an outside power source (pump driver, or prime mover) connected to the p ump shaft 36. The rotating shaft _ _ _ _ _~ the impeller.
t ur ns, or r otates
37. The parts of the pu mp fit together closely. A pum p is apt to leak where th e shaft passes i nto the pump _ _ _ __ ~~~
casing
38. Find the pack ing box. Wh ere the shaft passes into the casing, packing p r ovides a sea l to r educe _ _ _ _ __
leakage
39. The packing box may be fi lled with a flex ible packing material. This pack ing material pr esses around the _ _ _ _~
shaft
40. A mechanical sea l may be used inst ead of flexible
packing 41. 'Vhere the packing rubs against the s ha ft, the s haft may excessively.
wea r
42. In most centrifu gal pumps, part of the shaft is pr otected by a rem ovable s leeve. Find the sha ft sleeve. T he shaft s leeve can be more easily ~lIl d less expensively tha n the whole s haft.
replaced
43. Liquid leaks f rom the high-pressure area (discha rge) back into t he s uction area. Find the wear rings . The space between the eye (suction section) and t he casing (discharge section) is fitted with _ _ _ _ __
44. The casing wear ring is stutionary, and t he impeller wear ring rotates with the _ _ _ _ __
,
45. The close fit between the stationary weal' ring and the rotating weal' ring (increases/decI'eases) the amount of high-pressure liquid leaking back into t he inlet stream. 9
wear r ings
impeller
decreases
46. Some leakage is necessary for lubrication. Liquid leaking between the wear rings acts as a lubricant and coolant, and-keeps the rings from _ _ _ __ aga inst each other. 47. Worn wear rings are rem oved and replaced more easily and less than a casing or an im peller.
rubbing
expensively
48. As the rings become worn, clearance between them
(increases/ decreases), and more liquid flows f rom the discharge back into t he suction.
increases
49. The wear rings are lubricated and cooled by the
_ _ _ _ __ bleing pumped. 50. With out proper lubrication, the wear rings ca n come into with each other, get hot, and seize.
liquid contact
51. For this reason, a centrifugal pum p is never sta rted
unless it is filled with _ __ _ __
liquid
HOW CENTRIFUGAL PUMPS ARE RATED 52. Pumps are rated pa rtly according to their pumping characteristics. For exa mple, a certain pump delivers 100 ga llons per minute (GPM). This pump has a rated capacity of _ _ _ _ _ GPM.
100
53. Capacity is usually a factor in _ _ __ _ _ a pump.
rating
54 . Suction and di scha rge pressure also affect the rating of a pu mp. F or example, a pump produces a discharge pressure of 30 PSIG. It has a ratea discharge pressure of _ ____ PS fG.
30
55. Pumps are rated according to the things you need to know to operate t he pump efficiently. pump for Ratings help you select the your operation. 56. F or example, you need to pump out a huge tank quickly. If a ll other condit ions arc equal, a pump with a capacity of (100 GPlIi/500 GPM) is preferred.
best, or right, or proper
500 GPM
Capacity 57. The capacity of a pump is the amount of liquid t hat the pump moves in a given length of time. Capacity is usually measured in gallons per minute, abbreviated _ _ __ _ _ 10
GPM
58, Gallons, pounds, and cubic feet are measures of (amount/ time) .
amount
59, Minutes, hours, and days are measures of _ _ __ _
time
60. Check the measurements that are measures of both amount and time. _ _-"gallons per minute ___ pou nds per square inch ___,cubic feet ___ barrels per day
gallons per minute barrels per day
61. Pump capacity can be changed by changing the speed
of the impeller (RPM,
01'
revolutions pel' minute).
Increasing pump speed also (increases/decreases) pump capacity.
increases
62. The pump and its prime mover usually run best within a range of specific speeds. To increase the pump speed, you must also increase the speed of the _ _ _ _______ __
prime mover
63. Increasing pump capacity by increasing pump RPM's
(is/ is not) always practical.
is not
64. In a centrifugal pump, the liquid moves outward from the of the impeller toward the rim of th e impeller,
eye
65. Liquid travels from the inlet into the eye of the impeller. The liqujd is forced to move in a circular path by the rotating of the impeller. 66. Centrifugal force propels t he liquid (inward/ outward) through the rotating vanes. 67. Because the impeller is rotating, the liquid impeller is also _ __ _ __
III
vanes outward
the rotating
68. Circumference is the distance a1'ound a circle.
CIRCUMFERENCE
fo4-==:":"'::=Ooj
The distance ac,'088 a circle is called the (circumference/ diameter) . 11
diameter
69. Look at the drawing.
A B IMPELLER The circumference of impeller _ ______ is less than the circumference of impeller _______
A B
70. Because the shafts of both impellers rotate at the same speed, they both travel the same number of revolutions in a given length of time. .
But, liquid traveling around the outer edge of impeller B travels (farth ~r/th e same distance).
farther
71. The distance traveled aroun d a circular path in a given length of time is the tangential velocity.
Any point on the rim of impeller _ _~',---_---",_ h as the greater tangentia l velocity.
B
72. As a drop of liquid moveS outward from the eye, the in circu lar path it travels continually size.
increases
73. Because the size of the circular path continually increases, the tangential velocity _______ as the liquid moves outward from the eye.
increases
74. Thus, the larger the diameter of the impeller, the _ _ _ _ _ _ the fina l tangential velocity fo r a given
greater
RPM.
75. After the high-velocity liquid leaves the rim of the im~pelJer, it enters the casing where its velocity decreases. A large part of the velocity is conver ted to _ _ _ __
pressure
in the casing. 76, Increasing the tangential velocity increaaes the pres-
sure at the pump's dischal'ge. Without changing impellers,. tangential velocity is in creased by. (incr easing/ dee-reasing) pump speed. 77. Without changing pump speed, liquid can be pumped to higher elevations or higher pressures by _ _ _ _ __ the size of the impeller. l.-
78. Pump capacity ca n be increased by incr easipg pump _ _ _ ___ • or by using a larger _ _ _ _ __
12
increasing increasing
speed, or RPM j impeller
Pressure and Head 79. Pressure is the force acting on a unit of area (usually one square inch) . When force is measured in pounds, pressure may be stated as _ _ _ __ _ per square inch (PSI).
pounds
80. Head is the height of a liquid.
The head of this liquid is _ _ __ _ _ feet.
10
81. The pressure exerted by a head of liquid does not depend on the diameter of the container.
I---DI AMETER -
DIAMETER
-l
At any point on the bottom of the container, pressure depends only on the of liquid above that point.
head, or height
82. Pressure gages are set to fead 0 at atmospheric pressure (14.7 PSIA). ATMO SPHERI C PRESSURE
This gage is showing a pressure of _____ PSIG. 13
10
83. This pressure (includes/ does not include) the pressure of the atmosphere on the liquid.
does not include
84. Atmospheric pressure is _ _ _ __ _ PSIA (pounds per square inch absolute) .
14.7
85. An instrument that measures atmospheric pressure as well as tank pressure is measuring absolute pressure. This is written as pounds per square inch absolute. PSIA is an abbreviation for pounds per square inc h absolute 86. A pressure gage records only __- - - - pressure.
tank,
01'
liquid
87. Since a gage reads atmospheric pressure as 0, it is measuring gage pressure. PSIG is an abbreviation for pounds per square inch
gage 88. PSIA is always a (larger/ smaller) number than PSIG.
larger
89. Pressure in this tank is 43 PSIG.
Atmospheric pressure is 14.7 PSIA.
Absolute pressure in the tank is (more/ less) than 43 PSIA.
more
+
90. Absolute pressure is actually _ _ _ _ _ _ PSIA.
43
91. 43 PSIG and 57.7 PSI A are (the same amount/ different amounts) of pressure.
the same amount
92. PSIA = PSIG
+
14.7
93. PSIG = PSIA
14.7
94. A gage reads 30 PSIO. The absolute pressure in the tank is _ _ _ _ PSIA. 14
44.7
14.7, or 57.7
95. A 10-foot head of water makes a pressure gage read 4.33 PSIG.
100 F;E~E!.T
r::::l
4.33 PS1G
10 FEET
L~---.J f
A 100-foot head of water makes the gage read _ __ PSIG.
43.3
4.33 we can see tha, t f or each · 'd"mg 43.3 96 . B Y dIvt 100 or 10 foot of water, 0.433 PSIG is exerted.
A I-foot head of water exerts _ _ __ __ PSIG.
0.433
97. A IS-foot head of water exerts 6.49 PSIG (15 x 0.433). We can find out how much pressure a column of water of the water exerts by multiplying the by 0.433.
98. Because oil weighs less than water, a 10-foot head of oil exerts (more/ less) pressure than a 10-foot head of water. 99. A 100-foot head of crude oil and 100-foot head of water produce (the same pressure/ diffetent pressures).
head, or height
less
different pressures
100. The specific gravity of a substance is the weight of the substance divided by the weight of the same volume of water. The specific gravity of water is 1. A liquid with a specific gravity of less than 1 weighs
(more/ less ) than the same volume of water.
less
101. A I -foot head of water exerts 0.433 PSIG. A I-foot head of liquid with a specific gravity of 0.5 exerts PSIG.
0.5 x 0.433, or about .216
102. Water and a liquid with a specific gravity of 0.5 have the same height.
But the liquid with the 0.5 specific gravity exerts _ _ __ _ _ as much pressure as the water does.
half, or '12
Now look at Exhibit 2.
103. Exhibit 2 is a chart for converting head to pressure, or pressure to _ _ _ _ __
15
head
104. To read the chart, you must know the _____ _ _ _ _ _ _ _ of the liquid being pumped.
specific gravity
105. Suppose the head of a liquid is 200 feet and the specific gravity is 0.5. Using a straightedge, find the line between 0.5 on the specific gravity scale and 200 feet on the head sCc:'\ le. The pressure exerted by this liquid is about ___ _ PSIG.
43
106. Head can be changed to pressure; pressure can also be changed to head. Ey readin g a gage at the bottom of a closed tank, you can tell the of the liquid in the tank (if you know what the liquid is).
height, or depth, or head
107. Compare these two tanks of liquid .
. A
B
There is a greater head of liquid in (tank A/ tank B).
tank A
108. Look at the pressure gages to find which of these tanks has the greater head of liquid.
B
A
With the same liquid in each tank, (tank A/ tank B) has the greater head.
16
tank B
109. These tanks contaillliquids of the same specific gravity.
'--_ _~--'A The press ure reading wou ld be higher on (gage AI gage B). 110.
gage A
pressure sp. gr. X 0.433 Pressure = head x sp. gr. X 0.433 Head
Head may be expressed in terms of _ _ __ _ _ and pressure may be expressed in terms of _____
pressure head
Ill. Pressure; 30 PSIG Specific gravity ; 0.5
30 Head ; 0.5 x 0.433 30 0.216 about 139 feet For th is liqui d to exert 30 PSIG, the column must be about feet high.
139
H2. Head ; 10 feet Specific gravity = 0.5 Pressure - lO X 0.5 x 0.433 ; 5 x 0.433 2. 16 PSIG This liquid exerts (twice as much/half as much) pressure as the same head of water does.
half as much
113. Suction head is the sum of the pressure changed to ead, plusthe velocity changed to head, at the in let to t~ pump.
Dischm·ue head is the sum of the pressure changed to head, plus the velocity changed to head, at the _~_ _ __ of the pump.
discharge. or outlet
114. Velocity head is normally very small and is not used in pumping calculations. Suction head, then, is the _ _ _ _ _ _ at the suction, changed to head.
17
pressure
DISCHARGE
ACKING
BOX
CASING WEAR IMPELLER WEAR .......... SH.6.FT
\
I
.
EYE OF IMPELLER".",. f i""k .. ,,, ..
~' -
@ \
AFT
SLEEVE
m
><
%
'"....
-
EXHIBIT 2
10,000 100,000
.2
liorTIll l llll l ll l l l H 1111111 11111 11111 11111 11111 11111 11111 11t t Ll1 111 11111 11111 16 ... w
1001111 1111
::lfIrm l1i l fll ffff.mJif!iTImlIIII I III J1II I Mm; rnn
901I I I I I I t 451
__ "z I II I ITIIIITI 11 1111 I I I I I I1 11 H-! I 1111Il'kl 11111111111111111111111111111113
;as! Ill flit4PI III! 1IIII IIIIti tlll llll ll·.. ..... 1-
7Oi-H+ 7H:;; 3
1
V'
(}«-~
-
...w
«-
z 30
l Y l l ll l l lll l l l l l ,
0
1 11rl l 111 ~
[m[[ur
~IYl llll l llll lfml H
4ol+++ 4H... 2 0 I-
30
3 [-1 5
20
2 r iO
10
1
5 100
200
lliJOO IIT IJJ [JOO
500
600
700
CAPACITY. GPM
! ! I ! I ! ! I ! ! ! I J I I I II I I I I I
PERFORMANCE CURVES
m )(
:z:
...'"
..,
115. Discharge head is the pressure at the discharge, changed to _ _ _ _ __
head
116. Gages record the pressure at the pump suction and at the pump discharge.
The height of water in the suction tank exerts pressure, which is recorded on the (P ~/ Pd ) gage.
P.
117. Since the height of water is higher on the discharge side, the (Ps/Pd ) gage records the higher pressure. 118. The pump adds pressure to the liquid as it passes through the pump. The discharge pressure is actually the suction pressure plus the _ _ __ __ that the pump adds.
pressure
119. Even without a pump in the line, the liquid rises until it is equal on both sides.
POINT
3--- ----
.
\
~========o.::::J...-POINT
1
Without pumping, the liquid rises to point _ _ _ __
2
120. To move the liquid from point 2 to point 3, a _ _ __ may be used.
pump
121. The pump provides the _ __ _ __ needed to move the Jiquid above point 2.
energy, or pressure
18
122. The pump raises the liquid from the level of the suction tank into the discharge tank.
HEAD
The distance which the pump lifts the liquid is called the head. 123. The total head is the discharge head (minus/ plus) the suction head.
total minus
124. This pump is lifting water.
r .,
I
·...0:.",' ·.·.·A ••• '.'_,',
23 FEET
W'W'
~ 10
Y ;,
46 FEET
23 FEET '--....,
I
20 Discharge head = .1--:-:x"'0"".4"S"' 3 = 46 feet 10
Suction head
= "1---'-;X"'O <--.4'-'3"' 3 = 23 feet
Total head
= 46 - 23
= 23 feet
Actually, the pump only has to lift the water _ __ feet.
23
125, Total head can be estimated by measuring the height of liquid in the suction and discharge tanks and (addi ng/ subtracting) these heads.
subtracting
126. Or, total head can be calculated by reading the pressures at the pump suction and discharge and converting these pressure measurements to _ _ _ _ __
head
measurements. 19
127. This drawing shows a suction-lift system.
I
I
DISCH ARGE HEAD
TOTAL
HEAD
'Wi~*;:
:':!:
;'t
:" .'
-'-_.L_I ~,,;;;;···>;::~~:
d':
., If the pump is located above the suction tank, t he liquid t o the pump. must be
128. The distance t he liquid must be lifted to the pump is call ed the s uction _ _ _ __ _
lifted lift
129. The pump must supply enough energy to raise the liquid a distance equal t o the suction lift plus the discharge head. Suction lift plus discharge head is the _ _ __ _ _ head.
total
130. The pressure acting on the s urface of a liquid is transmitted throughout the liquid.
Sp.G •. = l
The gage on top of the suction tank records the presof the liquid. sure acting on the ,
20
surface
131. This pressure is 10 PSIG. The gage at the pump suction reads PSIG.
15
132. Of the 15 PSIG on the suction gage, 10 PSIG is due to pressure acting on the surface of the liquid. I
The remaining 5 PSIG is due to the _ _ _ _ _ _ of the liquid in the tank.
height, or head
ISS. Look at the drawing.
~~ntNmz:= ,~,« .~..-. :%;.
.
The actual height of the liquid in the suction tank is: 5 1 x 0.433 or ahout 11.5 feet. But the suction head is :
15
1 x 0.433 or about 34 feet. The suction head is greater than the actual height of liquid in the tank because of the exerted on the surface of the liquid .
pressure
134. For liquid to flow into the pump. there must be some pressure at the pump suction.
The pump (,vorks/cannot work) if absolute suction pressure is 0 PSIA.
cannot work
135. In a suction-lift system, suction pressure is provided by (the head of liquid/ atmospheric pressure).
atmospheric pressure
136. If there is no atmospheric pressure, then there (canl cannot) be a suction lift.
cannot
Vapor Pressure 137. Sometimes, when the absolute suction pressure is not high enough, liquids vaporize or evaporate at the pump suction.
To understand why this happens we must understand what makes liquids _ _ _ _ __ 21
evaporate, or vaporize
138. Heat is a form of energy (thermal energy) . Heating a liquid (increases/ decreases) its energy.
increases
139. When ice is heated sufficiently, the added energy melts the ice, and the solid ice becomes _ _ _ _ __
water, or liquid
140. If even more heat is added to this water, t he liquid water becomes steam, which is a _ _ _ _ __
vapor
141. When the liquid absorbs so much heat that vapors can escape from the liquid surface, the liquid evaporates. Evaporation occurs when _ ______ escapes from the IUrface of a liquid.
vapor
142. Vapors need energy to escape the liquid.
This energy comes from the _ _ _ _ _ in the liquid.
heat
143. Liquids and gases also exert a pressure on everything they touch.
Heating a fluid causes it to exert (ID2I.e/ leas) pressure.
more
/'144. In a liquid, the vapors exert a pressure before they
escape.
",,+ -L,IQUID SU RFACE
Vapor pressure is the pressure of the vapor that is trapped (above/ iD) the liquid.
22
in
145. Vapor pressure causes the liquid to vaporize, or evaporate.
The higher t he vapor pressure, the (more/ less) rapidly the liquid vaporizes.
more
146. The vapor pressure of a liquid is measured by finding the pressure that the liquid's vapor exerts in a closed container. At room temperature, gasoline has a higher vapor p~ssure than water. Therefore, the ______ will evaporate before the _ _ _ _ __ will. 147. Heating a liquid (Lncreases/ decreasea) its vapor pressure.
148. At higher temperatures, the same liquid-for example, water-has a (higher/ lower) vapor pressure.
gasoline water increases
higher
149. At the same temperature, different liquids have (the
different
same/ different) vapor pressures.
150. The hi ghe,' the vapor pressure of a liquid, the (more/ less ) heat it needs to vaporize.
less
151. There is also a pressure that is exerted on a liquid's surface by the gases and vapors above the liquid.
~1/ /l~ ,
GAS
'
The pressure on. a liquid tends to (cause/ prevent) the escape of vapors from the liquid. 152. To keep the liquid at the pump from vaporizing, the absolute suction pressure must be (higher/ lower) than the vapor pressure of the liquid at that temperature.
153. If the suction head of a pump is 8 feet, and the vapor pressure of the liquid (changed to equivalent head) is 9 feet, liquid (vaporizes/ does not vaporize).
23
prevent
higher
vaporizes
Net Posjtive Suction Head (NPSH ) 154. Net positive suction head (N PSH ) is the absolute s uction head minus the vapor pressure head.
If suction head is 50 feet and vapor pressure head is
35 feet, NPSH is _---"--1_
_ _ _ feet.
15
155. Or, NPSH auailable is the absolu te press ure at the pump s uction . changed to head. (pius/ minus) the vapor pressure or the liquid being pUlIl~CJ, changed to, _ __
minu s
head
156. NPSH required is the minimum head needed at the s uct io n to get the liquid into the impeIJer without vaporizi ng
157. If NPSH available is equa l to NPS H required, the pump may lose suction due to slight variations in pump design. If the NPSH available falls below the
TPSH required ,
does not operate
the pump (operates/ does not operate) properly.
158. NPSH available must be Imore/ lessl t han NPSH reo
morc
Quired .
159.
r------------------------------------------------, Absolute pressu re at pump suction -vapor pressure at pump temp . NPSH =
Specific gravity
s p. g r. X 0.433
=1
Vapor pressure = 15 PS IA Suction pressure
= 5 PSIG
Absolu te s uctio n pressure = 5 19.7 15
NPSH available =
+
14.7 = 19.7 PSIA
I X 0.433
about 10.8 feet I[
t he N PSH required is 8 feet. the pump Ioperates/
does not operale) properly.
160. NPSH available NPSH required
o perates
7.8 fcet 15 feet
The pump (operates/ does not operate) properly.
,
does not operate
Friction 161. Liqu id is flow ing l hrou g h this li ne.
•r:....
~}
\$.\. . . ". ; . . . . . . . . ... . . . . . . . ;.. .
A Pressure mu st be greater at (A l B).
B A
162. During flow, pressure is being converted to velocity. As velocity increases during flow, pressure (increases/ decreases) .
decreases
163. The pressure difference between A and B is called the 1J1'esslt1'e drop.
To increase the flow rnte, _ _ _ _ _ _ the pressu re drop.
increase
164. Fluid flowing through a pipe creates fl'iction.
Friction is a (driving force/ resisting force) for nuid flow. 165. POl' fluid to flow, the dl'i vin g force must be
resisti ng force
(gre~lter /
less) than the resisting fOl'ce.
greater
166. Or, the pressure drop must be greater than the amount of _ _ __ -:-
friction
167. As flow rate increnses, friction increases.
To overcome this friction, a _ _ _ _ _ _ press ure dl'op is needed.
higher
168. The more resistance the pipe offers to flow, the greater the pressure drop needed to move the liquid.
n,
.
.
-_._, I
A small pipe offers (more' less) resista nce than a large r pipe.
169. The pressure rirop needed is greater
111
more
the (Iarge/
small) pipe.
smal l
170. When the flow rate of liquid into a pump is increased, frictio n increases. Increasin g the flow rute _ _ __ _ _ the available suction pressure.
25
decreases
J 71. A smaller pipe is used on the suction of pump B .
. . . . ........_ J
B
Resistance to flow is g reater in pump (AlB ).
B
172. The ava ilable suction pressure is lower at (A/ B).
B
173. This mea ns that NPSH available may be too (high/ low) for the pump to operate properly.
low
174. With increased res istance to flow at the pump sllction,
liquid may _ _ __ __
vaporize
175. As the flow rate of the liquid increases, the suction pressure decreases, because the friction increases with fluid velocity. Some pressure is lost in overcoming _ _ _ _ __
friction
176. An incrcl.Ise in now !'ste increases friction and decrenses suction pressure.
The NPSH available (increases/ decreases).
decreases
177. Look at the drawing.
Sp. G.. = 0.5
The gage above the liquid reads _ _ _ _ _ _ PSIG. 178. The height of the liquid is _ __ ___ feet.
26
30
10
179. Pressu re due to the liquid level is :
Pressure = 0.433 x 10 x 0.5 = 2.16 PSIG. The gage at the pump suction should read 30 or PSIG.
+
2.16, 32.16
180. The gage at the pump suction actually reads 31.16
PSIG. The gage records a lower pressu re because some pressure has been used to overcome _ _ __ _ _ 181. If t he ,·e is no NPSH, liqu id _ _ _ _ _ _ at the eye.
182.
friction vaporizes
NPSH = Absolute suction pressure - vapor press ure at pump temp. 0.433 x sp. gr. Or, when the absolute suct ion pressure increases, the NPSH available _ _ _ __ _
increases
when the vapor pressu re increases, the NPSH ava ilable ______
decreases
when the suction head decreases, the NPSH available _ _ _ __ _
decreases
183.
Total head - di scharge head - suction head Or, wben the suction head increases, the tota l head decreases when the discharge head increases, the total head increases
Horsepower 184. A centrifuga l pump is operated by co upling its -,--.,..._ _ _ _ to the shaft of an outs ide powe r source (p rime mover, or driver).
shaft
185. !Iorsepower (HP ) is a unit used fo r measuring rate of work. Horsepower necessa ry to ove rcome friction and other losses and to move the liquid is provided by the prime mover, or driver 186. The amo unt of useful work that a pump delivers is t he difference between the pressure the liqu id has as
it ellters the pump and the pressure it has as it _ _ _ _ _ t he pump.
~
leaves
187. Pa rt of the horsepower put into the pump is used to
overcome friction and other losses; part goes to increase the pressure of the liq uid being pumped. The horsepower applied directly to the liquid is caned fluid
horsepower
'
27
188. The horsepower input is always (more/ less ) than the fluid horsepower, or horsepower output.
more
189. The overall efficiency of a pump is the percentage of the HP input that is transferred to the liquid leaving the pump.
A pump that operates at 100 HP input and 75 fluid HP has an overall of 75 %.
efficiency
190. The overall efficiency of a pump is found by dividing the HP output of the pump by the HP input, or HP output HP input If the HP input is 5 an d the fluid HP is 4, then the
efficiency of the pump is _ _ _ _ _ _ %. 191. If two pumps ha ve the same capacity, a low ~ effici ency pump requires (mo.t,e/ less) horsepower than a highefficiency pump t o move th e same amount of liquid at the same pressure and rate of flow.
80
more
192. The vol umetric efficiency of a pump is a measure of i ts internal leakage. The ma in source of internal leakage is the liquid flowing back between the wear rings from the discharge into th e of the pump.
suction
193. Volumetr ic efficiency is found by dividing the amount of liquid pumped by the amount of liquid pumped plus internal leakage: amoun t pumped amount pumped + inte·~l:·:n:'a'I'I-ea'k;-a-g'e In a pump di scharging 45 GPM, 5 GPM leaks between %. the wear rings. The volumetric efficiency is 194. As the wear rings become worn, the volumetric efficiency decreases and the overall efficiency _~_ __
90 decreases
Performance Curves F01' /1'al1te numbe1's 195 th1'ough 221 look at Exhibit 9, which shows a sample set 0/ performance curves /01' a centrifugal pump .
195. In the exhibit there are four curves which show the relationship of capacity to: _ __ _ _ _ head ; ____ _ ___ ; a nd
28
total NPSH efficiency HP, or horsepower
,
196. The graph in the exhibit is set up so that capacity is read at the bottom. Efficiency, horsepower, and total head are read at the
(left side/ right side) of the graph.
left side
197. NPSH is read at the ___' ---___ side.
right
198. Find the line on the graph for 200 GPM. This line crosses the NPSH curve at about _ _ __ on the NPSH scale.
3.8
199. If the pump is pumping 200 GPM, t he minimum NPSH required f or this pump is about
3.8
feet.
200. Find where the 200 GPM line crosses the efficiency " curve. From the efficiency scale on the left, you can read that
%
this pump pumps 200 GPM at abo ut efficiency.
65
201. The 200 GPM line and t he HP curve show that the horsepower required for this pump at 200 GPM is about
4.2 202. Look at the efficiency curve. Maximum efficiency on this curve is about _ _ _ %. 203. At maximum efficiency, this pump is pumping _ __
84 400
GPM. 204. Find the ot her performance values at 400 GPM. The HP required is about _ _ _ __ _
5.8
The total head is about
48
N PSH is
feet. feet.
205. This pu mp is more efficient when it is pumping (200/ 300)" GPM.
4.2
300
206. These pump performance curves were made up for a pump moving water. For more viscou s (thicker) liquids like oil, which re· sist flow more than water does, the curves shou ld be
adjusted for (higher/ lower) values.
lower
207. All centrifugal pumps come with a set of performance curves.
These curves can be used to find the NPSH, total efficiency. and _ _ _ _ _ _ for each pump at different capacities.
_ _ _ _ _~I
29
head;HP
,
208. The performance curves can also show some general pi'incipJes of centrifu gal pump performance. For example, look at the relationship between the total head curve and the capacity line.
When the total head decreases, t he pump capacity _ _ _ _ _ _ • except at very low capacity.
increases
209. §uppose the discharge valve of a pump is pinched down and the discharge head increases. The total head increases, and the capacity _____
decreases
210. As the level in the tank faUs, the suction head decreases.
The total head increases, and the rate of flow
~._ __
decreases
211. Look at the NPSH curve and the capacity line. As the pumplIlg rate increases, the NPSH required increases 212. Suppose the pump is operating at a point where the NPSH available and NPSH required are about equal and you try to increase the fl ow rate. The pump will lose ______
suction. or prime
213. Look at t he efficiency cu rve.
The efficiency of a pump is relatively _ _ _ _ __ at high and low flow rates.
low
214. For every pump. there is a capacity where the pump
oper.ation is most economical.
and therefore most
efficient
215. Look at the HP curve. As the flow rate increases. t he horsepower r equired
increases 216. Other factors affecting t he performance of a centrifu-
gal pUPlP are not shown on the chart. For example, a viscous (thick) liquid resists flow and is (easier/ harder) to pump.
harder
217. If the liquid being pumped becomes more viscous (for a given total head), the pump capacity is less.
The horsepower required to pump a viscous liquid is greater 218. Impellers of different sizes can be installed in a pump.
An impeller of _ _ _ __ _ diameter can pump to a higher head.
30
larger
219. To pump at a higher rate to a higher head requires more horsepower. When the size of the impeller is changed, neither the suction casing nor the size of the impel1er eye is changed. As the rate increases, the NPSH 1'equi1"ed in creases 220. The speed of turbine-ddven pumps can be controlled. ncreasi(g the speed has the same effect as installing an impeller of larger diameter in a motor-driven pump_ Decreasing speed has the effect of installing an impeller of _ _ __ __ diameter in a motor-driven pump.
gmaner
221. If the specific gravity of a material being pumped changes, the horsepower required changes. The capacity and head characteristics of a pump do not of the change when the material being pumped changes, but the hbrsepowel' required does change.
81
specifi c gravity
Section 2
Design and Construction of Centrifugal Pumps
SECTION 2
DESIGN AND CONSTRUCTION OF CENTRIFUGAL PUMPS
PUMP TYPES 1. Pumps are classified according to impel1er design and the number of impellers. A multistage pump has more than _ _ _ impeller .
one
2. A two-stage pump has _ _ _ impellers.
two
3. A two-stage pump has the same effect as joining _ __ single-stage pumps in seri es.
two
4. The fi rst pump discharges into the _ _ _ _ _ pump.
second
5. A multistage pump has two or more impellers mounted on onc _ _ __
shaft
6. The head at the discharge of the second impeller is greater than the head at the discharge of the first. The greater the number of impellers, the (higher Iqwer) the final discharge head is.
higher
7. Since liq uids arc nearly incompressible, a11 the impellers in t he pump are designed for about the same capacity. The impellers of a multistage pump are all about the _ _ _ _ size.
same
8. Pumps are also classified as single-suction or doublesuction. In a single-suction pump. liqu id enters from (onuide/ both sides) of the impeller. 9. 1n a double-suction pump, liquid enters through (one side/ both sides) of the impeller. 10. Since liqu id enters at both sides of the impeller, a double-suction pump is used for (high/ low) capacity operations.
one side
both sides
high
11. Double-suction pumps have lower NPSH requirements. When the NPSH available is low, a -suction pump is probably better suited for the pumping job. 32
double
12. Impellers may be open, partially open, or enclosed.
OPEN
PARTIALLY OPEN
ENCLOSED
In all three designs, the _ _ _ _ _ _ of the impeller is open.
eye
13. On an open impeller, the sides of the vanes (are/ lli
are not
nat) covered:
14. More liquid leaves the rim of the (open / partially open/ e.ru:.Iosed) impeller.
Flow is least controlled in the _ _ _ __ _ The _ _ _ _ _ _ come clogged.
enclosed
impeller.
open
impeller is the least likely to be-
open
Propeller Pumps 17. A propeller pump works very much like an impeller pump.
Instead of an impeller, the _ _ _ _ _ _ whips the liquid passing through it to high speed. 33
propeller
18. In this way the propeller adds _ _ _ _ _ _ to the liquid.
energy, or pressure
19. There are differences between impellers and propellers.
PROPELLER
IMPELLER
For example. liquid leaves the (propeller/ impeller) in the same direction as it entered.
propeller
20. Liquid leaves the (impeller/ propeller) at r ight angles to the way it entered.
impeller
~ l. Liquid enters the impeller only through the eye in the (impeller/ propeller) pump.
impeller
22. In the propeller pump. liquid enters the pump (through the eye/ through the blades).
through the blades
23. The area through which liquid enters the pump is smaller in the (impeller/ propeller) pump.
impeller
24. Therefore. the _ _ _ _ __ pump can handle larger capacities. 34
propeller
Turbine Pumps 25. The best features of the impeller pump and the propeller pump are combined in the turbine pump.
r PROPELLER
TURBINE
IMPELLER
The turbine pump is a mixture of the _ _ _ _ __ pump and the pump.
propeller impeller
26. The flow of liquid through a turbine pump is
r ___ like the How through a centrifugal pump. _ _ like the flow th rough a propeller pump.
___ halfway between the flow through a centrifugal pump and the flow through a propeller pump.
halfway between
27. The turbine pump, like a propeller or an impeller pump. can be single- 01' multistage. The multistage pump is used when you need a higher discharge (ClIp.city I head). 35
head Now tu rn the page, turn the book over, and go on .
28. Name the following pump designs.
A. single-suction
A.
B.
c.
B. double-suction
C. multistage
D.
D. propeller pump
E. turbine pump
E. 29. Which of these pumps are not centrifugal pumps?
D and E
( A!B/C ~D/E)
36
Vertical and Horizontal Pump. 30. This pump must move liquid up out of a water well, or pit, or any other source of liquid.
There (is/ is no) suction head available. 31. The pressure needed to move liquid into the pump sucpressure. tion must come f rom
32. If the well is dee p, atmospheric pressure (can/ cannot) push the liquid nil the way up into the pump suction. 33. One way to increase the NPSH available is to (increase/ decrease ) the distance liquid has to move up to get to the pump suction.
is no
atmospheric
cannot
decrease
34. Here the pump has been placed in the well liquid .
•
This gives the pump (more/ less) NPSH available.
37
more
85. Since the well is deep and narrow, the pump must be put in it (hor izontally/ vertically) .
36. To provide better NP SH, the pump is installed (horizontally/ vertically) and (above/ below) the level of the liquid. Because of the large amount of discharge head needed to lift liquid from a well, the turbine vertical pump is generally (single-/ mu lti-) stage.
vertically vertically; below
multi-
Pu mps Ope rating in Se ries or in Pa rall e l
87. When the discharge of one pump is fed into the suction of another pump, the two pumps operate in series .
... ...
... Pumps (A/ B) are operating in series.
A
38. When th e pumps are connected in series, the second pump takes liquid from the first and increases the discharge head. Putting pumps in series increases the discharge _ _ _ _ of the system.
head
39. The second pump cannot discharge more liquid than it receives from the first. Thus, pumps in series (shou ld/ should not) have about the same capacities. 38
should
40. Pumps that discharge into the same line are operating in pa1·allel.
Pumps (A B) are operating in parallel.
41. Operati ng pumps in parallel _ _ _ _ _ the capacity of the system. 42. With pumps operating in parallel, the total amount discharged equals the amount discharged from the first pump the amount discharged from the second. 43. Since liquid discharged from the first pump does not enter the second, the discharge head produced by the two together is (greater than / the same as ) the hCHd produced by each one separately.
B increases
plus, or
+
the same as
44. Pumps operated in parallel should have about the _"-,_ _ _ tobli head characteristics.
same
45. Pumps are operated in parallel to increase _ _ _ __
capacity
46. P umps are opera ted in series to increase _ _ __
head
47. Two pumps with similar capacity and head cha racteristics at a given s peed may be con nected in either _C~______ or _ _ _ _
par allel; series
48. To increase capacity, connect pumps in _ _ _ __
parallel
49. To increase head, connect pumps in _ _ _ __
series
39
Regu lating Pump Discharge 50. The amount of liquid discharged from a pump can be changed in a variety of ways.
A _ __ _ _ _ on the discharge can be open or
closed.
,
valve
61. By partially closing the valve, more _ _ _ _ _ _ is needed to get liquid out of the pump.
pressure
52. Pa rtially closing the va lve (increases/ decreases) the
decreases
discharge volume.
53. Here is another way to regulate the discharge volume.
BYPASS L INE
I
l A ______ line is connected to the discharge line.
40
bypass
54. An open < in the bypass line aHows liquid to flow through the bypass line as well as through the discharge Ii ne.
valve
55. When this valve is opened, some of the liquid from t he _ _ _ _ _ _ flows into the bypass.
discharge
56. Then it flows back to the pump's _ _ _ _ __
suction
57. This means that (more/ less) liquid is actually discharged from th e pump into the discharge line.
less
58. Being able to adj ust t he pump discharge is import ant when the pump may be moved and used for a _ _ _ _ _ _ operation.
MECHAN~AL
di fferent
DETAILS
Packing Box 59. The rotating shaft of a centr ifugal pump extends out through the casing so that the impeller may be coupled to the _ _ _ _ _ _ _ _ __
prime mover, or driver
60. The drawing s hows a typical pack}ng box.
CA SI NG
PACKI NG RINGS PACKING GLAND NUT
The packillg is f ormed around the _____ to mini. mize leakage of liquid from the pump. 61. The packing box surrounds the shaft where it enters the _ _ __
41
shaft
casing, or housing
62. Normally, the packing is fo rmed into rings which conform to the shape of the _ _ __
shaft
63. Packing muat be a low-friction materi al which is nonabrasive. Abrasive material damages the _ _ _ __ 64. To minimize leakage along the ahaft, the packi ng is _ _ _ _ _ aga inst the shaft.
shaft
pressed, or tightened
65. If the shaft is permitted to rub directly against the packing, the section of ahaft in the packing box wea rs 66. To keep f rom replacing the whole shaft due to packing wear, a is used to cover the section of shaft inside t he packing box.
sleeve
67. Packing must be a material that is not attacked and weakened by the liquid being pumped .
•
Packing which is weakened by the liquid permits some ' to the atmosof the liquid being pumped to phere.
escape, or leak
68. Packing is chosen for the _ _ _ _ _ being pumped and its temperature.
liquid
69. A packing gland at the (inner/ outer) end of the packing box holds the packing in place.
outer
The pressure necessary to compress the _ _ _ _~ against the shaft sleeve a nd control lea\cage is s upp lietl by the packing gland nuts. 70. A small amount of leakage between the packing and the shaft is necessary f or _ _ _ _ _ __
packing
lubri cation
71. The amount of _ __ _ _ _ is usually determined by company practices.
leakage
72. The packing gland holds the _ _ _ _ _ _ in place
packing leakage
and controls the amount of _ _ _ _ __ 78. [f the nut is tightened too much, the rubbing s urfaces may not be sufficiently _ _ _ _ _ _, and there may be excessive wear on the and the
74. Since insufficient lubrication may cause overheating, to allow the packing gland nuts must be amount of leakage specified by company practices .
•
42
lubricated shaft, or sleeve packing
adj usted
Lantern Rings 75. Look at the drawing.
LUBRICATING
The lantern ring is a metal cage about the size of a packing ring that fits around the inside the packing box.
sleeve
shaft
76. The lantern ring provides a space between the packing rings near the center of the packing box which can be su pplied with lubricating or seal _ _ _
oil
77. The lantern-ring arrangement shown differs from ring packing in the way it is _ _ _ _ __
lubricated
78. The lubricating fluid can be liquid from the pump liquid from outside the pump.
01'
When a corrosive or erosive ]iquid is being pumped,
lantern-ring lubrication from
(another source/ the another source
pump) is used. 79. Lubricating fluid is pumped into the packing box under pressure higher than the pressure inside the casing. This pressure keeps the liquid in the pump from entering the _ _ _ _ _ _ __
packing box
80. Lantern-ring packing is also used in a pump operating at less than atmospheric pressure. When the pump operates under vacuum, air may be pulled into it during operation.
To keep air out, the pressure of the sealing-lubricating fluid must be (above/ below) the pressure of the atmosphere.
43
above
8].
[n a pump operating under vacuum, t he lubricating liquid is usually the liquid being pumped, if t hat li quid is nonc9rrosive. I t is pumped into the packing box at a pressure above
atmospheric
pressure. 82.
Pump A is pumping a light oil. Pump B is pumpi ng acid. (Pump A/ Pump B) is fitted with a lantern ring .
83.
Pump B
Liq uid leaking from the pump is a hazard, especially if it vaporizes at a low temperature. Lea kage ca n also be expensive. Therefore, pump packing should be _ _ _ _ _ _ _ fre· quently to make sure it is operating properly.
checked
Mechanical Seals 84.
Mechanical seals are morc widely used than shaft packing because they require less maintenance and hold leakage to a minimum.
SPRING HO
R
SEAL OIL OUTLET
STATIONARY SEAL RING (Carbon)
RING SEAL INLET
ROTATING SEAL RING
L FLANGE
(H a,d .Su ,face Metal}
The other element rotates with the _ _ _ __
shaft
85.
The stationary seal ring is us ually made of _ _ _ _ _ _.
carbon
86.
The rotating seal ring is fa ced with special metal where it co mes in contact with the ______ seal ring.
stationary
44
87. The spring holder is held in place on the shaft by a set screw. The compression ring and the rotating seal ring are free to move along the _ _ _ __
shaft
•
88. The springs push against the compression ring and conipress the flexible O-ring against the shaft and the rotating seal members, to prevent at this point.
leakage
89. The a-ring is made of rubber or some other flexible material, depending on th e liquid being pumped. It makes a tight ______ between the rotating
seal
elements and the shaft. 90. Heat is generated between the stationary and rotating faces. Oil is circulated in the packing box to cool and _ _ _ _ _ _ the seal. 91. The lubricant also helps to keep corrosive or ____ _ material out of the seal.
lubricate erosive
92. A single seal has one set of sealing faces. This seal has two sets of sealing faces.
CASING
SEAL OIL TLET
STATIONARY SEAL RING
It is a
STUFFING BOX FLANGE
seal.
45
double
Impeller Thrust 93. During operation, pressure in the discharge por tion of the casing is greater tha n the press ure in the suction portion.
•
SUC TI ON ..... PRESSURE
DISCHARGE PRESSURE
The discharge pressure acts on the right side of the impelier, exerting a fo rce to the (left/right).
left
94. The discharge pressure acting on the ri ght side of the impeller exerts a force to the left. The suction pressure acting on the left side of the im pe ller exert s a fo rce to the _ _ _ _ _ __
95. Since the s uction pressure is less than the discharge pressure, the tota l force acting to the left is _____ than the force acting to the right.
rig ht
greater
96. This imbalance of forces creates thrust along the shaft. To overcome th is thrust and hold the _ _ _ _ _ __ in its proper position, a thrust bearing is used.
impeller
97. Both sides of the impeller maintain close clearance with the casing.
THRUST BEAR ING
HOLE r~~~
=f-C:OLLAR
R RING
WEAR R
Wear rings at the eye minim iZe leakage f rom the _ _ _ _ _ _ back to the suction. 46
discharge
98. A collar at the back of the impeller has the same inside dimension as the suction eye. Wear rings between the collar and the casing minimi ze
_ _ _ _ __ into the collar .
leakage
99. Any leakage into the collar flows back into the suction
th rough a hole in the impeller. This hole equalizes pressure between the left and rig ht
sides of the _ _ _ _ __ 100. Since the
impeller
on both sides of the impeller
pressure
is about equal, there is almost no thrust. 101. In multistage pumps , several methods can be used to mini mize thrust. Some pumps are constr ucted so that some of the impellers face one wayan the shaft and the others face the other way. One set of impellers offsets the
of the others.
thrust
Balancing Drum 102. When all impellers are installed in the same direction on the shaft, thr ust may be red uced with a balancing
drum.
BALANCING DRUM ATTACHED TO SHAFT
BALANCE LINE TO
ION
The tb.rust created by each impeller acts to the (left I right) .
47
left
103. The total impeller thrust is the sum of the thrust of all the impellers. The pressure acting on the left side of the balancing drum is the pump pressure.
discharge
104. The space on the right side of the balancing drum is open to the suction. Th is space is at _ _ _ __ pressure.
suction
105. The pressure difference across the balancing drum creates a force acting to the right. The drum is sized so that this force balances the impeller _ _ __
thrust
106. The Bman clearance between the balancing drum and the cas ing minimizes leakage from the discharge back to the suction.
As wear increases, this clearance increases, and the volumetric efficiency of the pump _ _ _ _ __
decreases
ALIGNMENT AND VIBRATION 107. The pump and prime mover are joined by couplings.
The pump and _ _ _ _ _ _ _ __ _ properly aligned.
must be
108. If the pump is handling hot liquid, ihen t he pump should be heated to near operating _ _ _ _ _ _ to check alignment.
prime mover, or driver
temperature
109. Improper alignment of the pump and prime mover puts a strain on the shaft and may wear or break the shaft or couplings.
Improper alignment may also cause bearings and seals to excessively or fail. 110. Improper ali gnment may also damage wear rings, and permi t the impeller to against other parts.
wear
rub
111. Any improperly balanced rotating assembly may cause excessive vibration. Misalignment of pump and prime mover or partially blocked impellers may also cause _ _ _ _ __
vibration
112. Cavitation in the impeller is the continual forming and collapsing of vapor bubbles in the liquid . Cavitation may cause the pump to _ _ _ _ _.
48
vibrate
113. So'}'etimes vibration can be beard, or detected by _ _ _ _ _ the pump.
feeling
114. Many pumps are equipped with gages and meters which _ ____ vibration.
detect
115. Excessive vibration is a sign that something is wrong with the pump. If unusual noise or vibration occurs, the pump must
be ____ _____
38
soon as possible.
shut down
LUBRICATION Wear Rings 116. Wear rings sirnpjj.fy maintenance by protecting the casing and the _ _ _ _ __
117. Wear rin gs are lubricated only by the _ _ __ pumped.
being
118. Wear rings are not properly lubricated if the liqui d in the pump vaporizes or if the pump runs _ _ __
impeller
liquid
dry
The Packing Box 119. Packing must always be lubricated. Normally, ring packing is lubricated by the _ _ _ __ being pumped.
liquid
120. The lantern ring and packing are lubricated by an oil pumped to the ring, especially if the pump is handling _ __ __ _ 01' erosive liquid.
corrosive
121. Some packing boxes are lubricated by grease cups instead of _ __
oil
Bearings and Couplings 122. The pump shaft must rotate with the least friction
possible. Resistance to the rotation of the shaft must be as possible.
_ _ _ _ _ a8
small
123. The impeller must be kept in position while it rotates.
l t must be free to rotate, but not to _ _ _ __ in other directions.
49
move
124. Besides rotating, the shaft may tend to move in two
other ways.
AXIAL MOVEMENT (THRUST)
ROTATION (TURNING)
> RADIAL MOVEMENT
In most pumps, more of the area of the impeller is exposed to discharge pressure than to suction pressure. This unbalanced pressure causes a to be exerted in an axial direction.
force
125. Movement can also occur if the pump has a long, un-
supported shaft, or if the impeller is out of balance. This is (axial/radial) movement. 126. Both radial and axial movement must be _ _ _ _ __
radial controlled, or minimized
if the impeller is to remain in position. 127. Bearings support the shaft and allow it to rotate with
very little friction. Bearings also control ______ and ____ __ movement of the shaft.
axial; radial
128. The bearing lubricant provides a fluid film between the
rotating shaft and the bearing. This fluid film prevents the shaft and its stationary supports from against each other. 129. A radial (journal) bearing on which the shaft rests controls movements.
rubbing radial
130. A thrust bearing limits end-to-end movement of the shaft.
A thrust bearing limits the amount of (axial/radial) movement. 50
axial
131. Some pumps use ball bearings to control both radial and thrust movement.
RING SHAFT
TWOIIST
BALL BEARING
The shaft of this pump is supported by both _ _~''"'<'<'" and baH bearings. 132. Ball bearings are lubricated so that there is almost no _ _ __ _ _ between the ball and any of the other parts it touches.
133. The ball bearings _ _ _ _ _ _ freely as the shaft rotates.
thrust radial wear, or friction turn
134. BaIJ bearings may be grease- or oil-lubricated. Wh ere the load on the bearing is great and considerable heat is generated, oil is used as the lubricant because it also the shaft and bearing.
cools
135. Grease-packed bearings can be overgreased. Overgreasing causes the bearing to _ _ __ _
overheat
136. Slinger rings are also used to move lubricating oil from the reservoir to the bearing. BE ARI
1-~--4--l,LI NGER RING
_ _ _mr-u IL RESERVOIR
A slinger ring fixed to the shaft and rotating with it throws oil from the reservoir onto the ~_ _ _ __
51
bearing
187. Large pumps use heavy-duty sleeve bearings instead of ball bearings.
EARING CONTAIN ER FILM
BEARI NG BEAR ING BRACKE T A sleeve bearing has (more/ less) surface area than a ball bearing does.
more
138. A sleeve bearing can support a very _ _ __ __ shaft.
heavy, or large
139. Sleeve bearings control (radial/axial) movement.
radial
140. The bear ing is made of low-friction metal (babbitt) and is lubr icated by a film of _ _ _ __ _ .
oil
141. The oil is supplied to the bearing under pressure through grooves on the bearing surface. The high.pressure oil insures that the shaft (can/ cannot ) squeeze the fi lm of oil out of the bearing under heavy load. 142. The shaft rotates on a film of , and there is no direct contact between the shaft and bearing. 143. Oil can be supplied to a sleeve bearing either oil ring or under pressure by a lube-oil pump.
cannot
oil
b~n
SL EEV E BO " .I
IL RING OIL RESERVOIR
The oil ring picks up oil from a _ _ _ __ _ below the shaft.
52
reservoir
144. The ring rotating on the picks up oil from the reservoir and ca rries it up to the bearing.
shaft
145. In a press urized oil system, oil is pumped to each bearing 146. Lube·oil pumps are used when the load on the bearings is great. Where possible, t he press ure lube·oil system should be working before the pump is started so that there is an oil film betwee n the shaft and the _ __ __
bearing
147. Pumps with a large axial load use a babbitt-faced (antifriction) thrust bearing. BABBITT . FACED THRUST SHOE
THRUST SHOE RETAINER
SH
FT
PUMP BEARING BRACKET
T
ST COLLA R
The th r ust collar rotates as part of the _____
shaft
148. The stationa ry t hrust shoes restrict axial movement of the shaft. The shoes a re pivoted to absorb minor va r iati ons in th e rotation of the thrust _ _ __ _ _ 149. Oil may be pumped to the bearing, or the bearing ma y run in oil to mai ntain a lu bricat ing between the surfaces.
collar film
150. The temperature of the lu bri cating oil must be maintained within t he operati ng r ange. If the temperature rises too high, bearings m,lY _ _ _ _ _ and fa il.
overheat
151. Many pump coupli ngs are lubr icated with heavy oil or grease. Before the pump is started and during operation, the couplings should be checked for lubri cation and leakage 53
152. The operating manual or the s upervisor specifies the _ _ _ __ and amount of oil to be used for lubricating the co upling.
gr ade
153. Oil must be free of di rt and water. Wat er breaks down the film between the shaft and bearing, and _____ is abrasive.
dirt
PUMP COOLING 154. Pumps performing heavy-du ty service and pumps ~ n g hot liquids may be water-jacketed. Pump parts subjected to _____ temperatures a re surrounded with water jackets. 165. "Vater is circulated to cool the lubricati ng oil, packi ng, and other parts where tem peratures may develop.
high
hi gh
156. F riction between the shaft and packing creates heat.
Sometimes the heat generated in the packing box area is too great to be carried away by the _ _ __ __ or the lubricant.
157. To keep the shaft and packing from overheating, they are fitted with ________ __
air
water jackets
158. Look at th e drawing. CASING
SHAFT
SLEEVE
PACKING:!i2
GLAND
The cooling water circulates in the _________ surrounding the packing box.
54
water jacket
169. When the bearing lubricant must be cooled, the bearing and reservoirs may be su rrounded with _ _ __
water
iackets 160. Where the heat generated is too great to be ca rried away by water-jacketed reservoirs, the lube on is
pumped through a shell-nnd-tube cooler and then to the _ _ _ __ _ 161. If not much heat is generated by t he pump, heat is lost directly to the through the reservoir
bearings
air, or atmosphere
housing. 162. High temperature pumps usually have water-j acketed
bases (pedestals). The more heat the pump has to handle, the more
thoroughly it is _ _ _~ ._ __ __
65
water-jacketed
•
Section 3
Operation
SECTION 3 OPERATION STARTUP be checked to assure that they will deliver a supply of clean and dry lubricant all the time that the pump is in service.
1. Pump-lubricating mechanisms must
continuous
2. If bearings take grease instead of oil, grease fittings must be routinely greased and grease cups must be filled.
Do not _ _ _ _ __ the bearings.
overgrease
3. The temperature of pumping equipment may be increased either by the liquid being pumped or by friction.
Parts of the pump which cannot tolerate increased temperatures are provided with systems. 4. If the pump is handling hot liquid, the packing box is usually to prevent the packing from deteriorating.
cooling
cooled
5. Surfaces of mechanical seals are cooled. If the surfaces get too hot, wear and deterioration (i ncrease/ decrease) .
increase
6. Bearing housings may be cooled to maintain proper
Clearance. If a bearing overheats, it may expand and freeze to the _ _ _ _. 7. Pump pedestals may be cooled to maintain alignment between the pump and the _ _ _ _ _ _ _ _ __
shaft prime mover, or driver
8. Before starting the pump, the complete _ _ _ __ and systems should be checked and in good working order.
cooling lubricating
9. Cooling
water
must be circulating through all water-cooling systems.
10. A pump that is to handle hot liquid should be warmed before it is started to prevent damage from unequal expans ion of parts . Unequal expansion may permit contact between the stationary and _ _ _ _ _ parts.
11. The pump should be warmed gradually by slowly circulating hot thr ough the pump.
56
moving
liquid
12. A spare pump in hot service is usually kept warm by using a small circulating Hne from the _ _ __ _ __
discharge
of the operating pump. 13. Steam tracer lines may be ,run alongside lines to and from the pump to keep liquid within the proper vis-
cosity range so that it flows freely. Steam tracer lines should be operating (before/ after) the pump is started.
before
14. After the prime mover has been checked for proper lubrication and is ready to operate, if the pump shaft is accessible, it should be turned by hand to see that it
is free to _ _ __ __
rotate
\ 15. When a newly installed or reconditioned prime mover is returned to service. the direction of its shaft rotat ion
should be checked before it is pump.
to the
coupled
16. All valves that contt·ol the flow of liquid into and out of the pump should be set according to instructions. If the valves are not set properly, the wrong liquid
may be pumped, or liquid may be pumped into the _ _ _ _ _ _ place.
wrong
17. On most pumps , the discharge valve is closed when the pump is started.
Clos ing the discharge valve (increases/ decreases) t he
decreases
pumping rate. 18. Horsepower requirements
decrease
19. At low rates the pump is less likely to lose _ _ __ _
suct ion
as rate de· creases, and the prime mover is less likely to overload.
20. If the suction va lve is closed, no liquid can enter the pump.
The pump is started with the suction valve (open/ closed) . 21. When practical, a centrifugal pump is started with the discharge valve ; the suction valve is always
open closed open
22. A spare pump with an automatic startup device must
be set with both the suction and the discharge valves open 23.
Centrifugal pumps should never run dry , because they overheat. Most centrifugal pumps should be primed /some vertical centrifugal pumps are self-priming if they are submerged in the liquid . The pump is primed before startup by filling the casing
with
~_~
_ _ _ __
liquid
57
24 . Liquid is brought into the pump by venting the casing. ~he vent mu st be open to allow vapors to excape from the pump case.
If the liquid being pumped is dangerous, venting should ~e
done to (an open / a closed ) system.
~5 . Care must be taken to make sure that the suction line to the pump remains full of _ _ __ _
a closed
liquid
26. Vapor rises from the liquid, and vapor pockets are apt
to form at (high/ low) points in the suction system.
high
27. Unless vapor pockets in the suction line are vented off, they can work themselves into the pump and cause the
pump to lose _ _ _ _ __
prime, or suction
28. The suction line is usually provided with vent valves
at high points in the line through which -""~r-- may be vented.
vapm."
29. With the prime mover functioning properly, the pump is ready to start if: all bleeders, vents, and drains are _ _ _ _ _ __
ClOSEd
the _~_ _ _ _ _ and _____ ~stems are checked,; the _'_____ tracer lines are turned on ;
lubricating, cooling steam
the discharge and suction _ _ _ _ _ are properly set;
valves
the pump is _ _ _ __
primed
30. When all systems have been checked and th e pump has been primed, the pump is ready to operate.
Then the _ _ _ _ is started. 31. When the pump is up to speed, the _ _ _ _ _ valve
pump, or prime mover discharge
is slow ly opened. 32. If the discharge pressure remains normal and steady, then the pump has taken and is operating
suction
as it should. 33. If t he pump operates for any length of time with the di scharge va lve closed, it may overheat. Then liquid may _ _ _ _ _ _ , and the pump loses s uction.
vaporize ,
34. If the di scharge pressure does not rise, or if it rises and then drops again, the pump has probably lost its suction. or prime
35. If the pump has lost its prime, the pump must be shut down and then _ _ _ __ _
58
reprirned, or primed
36. The pump should be checked for leaks in the casing, packing box, flanges, and bleeders. The packing-box gland should be checked to see that ~
is sufficient for packing 1ubrication,
~
leakage
not excessive.
37. The temperature of the packing and bearings should be checked, usually by touching them. Poor lubrication, poor cooling, or mecha nical trouble may be indicated by temperature.
38. The coupling should be checked to be sure it is not _ _ _ _ _ _ lubricant.
increased leaking
39. Period ic checking should assure that operation stays smooth and continuous.
If unusual noises develop, the _ _ _ _ _ should be
cause, or trouble
determined.
40. It may be necessary to correct pumping conditi ons. If the trouble is mechanical, the pump should be shut down
SHUTDOWN 41. If the pump is to be taken out of service, then it must be properly shut down. The drivel' is shut down and locked out to be sure that it is not again by accident.
started
42. If the pump is equipped with a remote emergency shutdown device, you may try th is device now to see if it works
43. The suctiqn and discharge va lves are closed and all liquid is _ _ _ _ _ from the pump to a safe location.
drained
44. The lubricating and cool ing systems are sh ut down .
If freezing is likely, then water must be drained f rom the system. 45. If the pump drains completely, the suction and discharge valves are tightly _ _ _ __
cooling
closed
46. Steam lines are left on or turned off depending on the operating situation.
tracer
47. If the pump is to be worked on in place, _ _ _ __
blinds, or blanks, or plugs
must be insta1Jed in the lines in accordance with company practices.
59
48. If the pump is to be taken to the shop for repairs, it is py,rged or flushed out, disconnected from the base, and ,
are installed on the process lines .
blinds, or blanks, or plugs
49. Hazardous vapors or liquids are purged from the pump with an inert material. The pump
IS
purged with steam or washed with
water 50. If a pump is goin g to be set as an operating spare, the
cooling and flushing systems are left operating, and the suction and discharge valves may be left open in the line.
The pump is ready to _ _ _ _ __
start, or operate
51. Usually. a check valve in the discharge li ne prevents liquid in the line from backing up through the spare
pump 52. During shu tdown the check valve should close automatically.
If liquid should leak back through the spare, then the pumping system loses __' _ _ _ _~
capacity
COMMON PUMP PROBLEMS Gradual Loss of Pump Capacity 53. Foreign material in the impeller causes the pump to lose capacity. Foreign material in the impe ller may also calise imbalance and damage the pump. If the liquid is apt to contain _ _ _ _ _ _ material, strainers 01' screens are used.
foreign
54. A pump in a new installation or where extensive work has been done upstrea m shou ld be protected by a screen
installed in the (suction/ discharge) line.
suction
55. The screens. may be removed when no more blocking material comes through the suction line. Normally, screens are not necessary with _ _ __ _ liqu id.
clear, or clean
56. Pump capacity decreases if the prime mover, such as
a turbine, (loses/ gains ) speed.
loses
57. If the balancing drum is worn, a pump may lose capacity. Too much liquid circulates back into the suction of the pump when the clearance between the drum and the casing _ _ __ _ _
60
increases
58. Pumps lose capacity when worn wear rings anow liquid in the discha rge section to flow back into the of the impeller. 59. Thus, liquid that should be leaving the pump with the discharge is returned to the
eye
suction
60. lf the tips of the impel1er vanes become worn, the pump
moves (morelless) liquid.
less
6l. If there is blockage in t he discharge line, the total head and the rate decreases.
increases
62. Look at the graph.
60
" 40 TOTA L HEAO
20
o
"
'\
\
\
BOO 400 600 CAPAC IT Y ( PU MPING RATE , GPM)
200
1000
As total heed increases, the rate (increases/ decreases .
decreases
63. The head increases to overcome the additional frictional resistance. and the rnte decreases. Incl'easing head and decreasi ng rate indicates that the
_ _ _ _ _ _ line may be partially blocked. 64. Rate may decrease because of a partially plugged strainer in the line.
discharge
suction
65. Common causes of reduced capacity are: worn wear rings allowing liquid to _____ from
leak
the discharge to the suction ; increasi ng total head due to an increase in discharge pressure or a decrease in suction pressure; foreign material in the _ _ _ _ __
impeller
pump turbin e losing _ __ _ __
speed
worn balancing system or worn _ _ _ _ __ vanes;
impeller
plugged strainer in suction.
61
Reconditioned Pump Returned to Service-Capacity Still Below Normal 66. Some obstruction may still remain in the ______ or discharge lines.
s uction
67. If an electric motor has been improperly wired, the impeller may be ______ in t he wrong direction.
turning
68. Unless the prime mover (steam turbine) has a lso been checked and repaired, it may be still delivering insufficient _ _ _ _ __
power I
0 1'
Pump Functions Properly at Low Rates - Loses Suction at High Rates 69. The NPSH available decreases when the suction li ne is plugged. If NPSH is too low, the pump (can/ cannot) handle
cannot
high rates.
70. One common obstruction in t he sucti on li ne is a partiall y plugged suction _ _ _ _ __
strainer
71. If the eye of the impeller is parti a lly blocked, th e NPSH requirement of the pump (increases/decreases).
increases
72. If the suction temperature increases or lighter material is being pumped, t he vapor pressure _ _ _ _ __ and the NPSH available dec reases, for any given rate.
increases
Motor Kicks Off, Engine Logs, or Turbine W ill Not Get Up to Speed 73. Normally, a pr ime mover is chosen to handle a specific liquid. If a different liquid is pumped, the prime mover may
be _ __
_
ovel'loaded
74. If an electric motor keeps kicking off. it is usuany overloaded . If a turbine does not get up to speed, it may also be
overloaded 75. \Vhen the amount of work required to pump t he liquid
is (greater/ less) than the work output of the driver, a motor continually kicks off, or a turbi ne does not get up to speed.
greater
76. If the prime mover is not designed to hand le the required ca pacity, this problem may be corrected by _ _ _ __ _ the rate of the pump.
62
decreasing
speed
77. Liquids of higher specific grav ity are heavier than liquids of lower specific gravity.
If a liquid of high specific gravity is substit uted for one of lower specific gravity. the prime mover may be overloaded
78. The viscosity of a liquid may also cause the prime mover to overload.
A liquid of higher viscosity is (harder / easier) to pump.
79. Overload ing may be corrected by increasing the size of the ____________ or by decreasing the of the pump. 80. Capacity may be decreased by changing the impeller to a diameter 01' by slowing the _ _ _ __
81. If packi ng fits too tightly against the shaft, friction (increases/ decreases ) and may cause the prime mover
harder prime mover capacity smaller; pump. or prime mover increases
to overload.
82. Loosening the packing _ _ _ _ _ may reduce the
gland, or nut
f riction.
83. If the casing is warped, the impeller may not rotate freely . This restriction on the impeller may _ _ __ __ the prime mover.
overload
84. A damaged impeller or wa rped casing must be repaired
or _ _ _ __
replaced
Pump Continually Loses Suction 85. A pump that continua lly loses s uction may be im-
properly primed and may have a _~_ _ _ pocket
vapor
in the suction line. 86. An air leak in the suction system of a pump operati ng under vacuum may cause the pump to lose its "'_ __
prime
87. The seal li ne to the packing box of a pump operating under vacuum may be blocked, and _ _ _ _ __
ail'
may enter the pump through the packing. 88. If a lantel'll ring is out of place in a pump operating at va cuum, it may prevent sealing liquid from entering
the packing box. If air enters the pump _ _ _ _ _ , t he pump will probably lose its prime.
auctio n
89. If the pump is operating very close to the NPSH limit, the pump may in termittently lose its _ _ _ __
prime, or suction
90. If suction strainers are partially plugged, the NPSH ava ilab le is (higher/ lower) t han normal.
lower
Cavitation
91. Cavitation is the formation and collapse of vapor bubbles in the _ __ __
liquid
92. Cavitation occurs when the pump is operating near the minimum NPSH.
When cavitation occurs, some of the liquid flashes to
vapor 93. If this happens in the suction section or at the eye of the impeller, the vapor bubbles are carried into the impeller
94. As the pressu re • the vapor bubbles collapse in the vanes, and the Hquid rushes in with such force that it knocks off little particles of the metal vanes. This causes pitting and erosion of the _______
increases
vanes, or impeller
95. The violent col1apse of the vapor bubbles causes a C1'ackling noise in the pump. which is a good indication of _ _ _ __
cavitation
96. To correct cavitation, the NPSH available must be _____ or the pumping rate must be _ _ _ __
increased; decreased
97. The NPSH available may be increased by decreasing t he rate of the pump. By throttling (partly closing) the discharge valve, the rate may be _ _ _ _ __ 98. NPSH available may also be increased by increasing th~ level of liquid on the (auction/ discharge) side of the pump.
decreased
suction
99. Decreasing the pumping rate may r estore operation to a range where sufficient NPSH is available at the pump suction. If the crackling noise stops, the adjustment (has/ has
'"11ot) corrected the cavitation. 100. To correct cavitation: _ _ _ _ _ _ NPSH available or _ _ _ _ __ rate, which decreases NPSH required.
has
increase; decrease
101. Cavitation is an operating problem. Cavitation becomes a mechanical problem if the pump is by the effects of cavitation. 64
damaged
FEATURES OF THE CENTRIFUGAL PUMP 102. Since the impeller of a pump rotates smoothly, the flow of liquid from the pump is (smooth/ pulsed).
smooth
103. If the discharge of a positive displacement pump is blocked off, excess pressure may build up in the casing
(depending on the type and size of the prime mover). The flow of liquid can be stopped in a centrifugal pump without building up excessive in the
pressure
casing, because the impeller can still move freely.
104. Thus, the prime mover (is/ is not) overloaded.
is not
105. Even though pressure does not build up excessively. energy is imparted to the liquid remaining in the pump.
This energy is used up as friction. The fluid in the blocked pump (may/ may not) overheat.
may
106. Since at low flow rates or no flow, the liquid tends to
_ _ _ _ _, it is not recommellded that centrifugal pumps be operated below 10 % of rated capacity.
overheat
107. Where low rates are of concern, a discharge-to-suction bypass and a cooler may be provided.
This assures that sufficient _ _ _ _ _ is circulating through the pump at all times.
liquid
108. Centrifu gal pumps are simple in construction and rela-
tively (inexpensive/ expensivej to build.
65
inexpensive
