Section A -- Centrifugal Pump Fundamentals A-1 Head The pressure at any point in a liquid can be thought of as being caused by a vertical column of the liquid which, due to its weight, exerts a pressure equal to the pressure at the point in question. The height of this column is called the static head and is expressed in terms of feet of liquid. The static head corresponding to any specific pressure is dependent upon the weight of the liquid according to the following formula.
A Centrifugal pump imparts velocity velocity to a liquid. liquid. This velocity energy is then transformed transformed largely into into pressure energy as the liquid leaves the pump. Therefore, the head developed is approximately equal to the velocity energy at the periphery of the impeller This relationship is expressed by the following well-known formula
Where H ! H ! Total head developed in feet. v ! "elocity at periphery of impeller in feet per sec. g ! #$.$ %eet&'ec$ (e can predict the approximate head of any centrifugal pump by calculating the peripheral velocity of the impeller and substituting into the above formula. A handy formula for peripheral velocity is
D ! )mpeller diameter in inches V ! "elocity in ft.&sec The above demonstrates why we must always think in terms of feet of liquid rather than pressure when working with centrifugal pumps. A given pump with a given impeller diameter and speed will raise a liquid to a certain height regardless of the weight of the liquid, as shown in %ig. *.
Fig. 1 Identical Pumps Handling Liquids of Different Specific Gravities.
All of the forms forms of energy involved involved in a liquid flow flow system can be be expressed in terms of feet of liquid. liquid. The total of these various heads determines the total system head or the work which a pump must perform in the system. The various forms of head are defined as follows. '+CT) )%T exists when the source of supply is below the center line of the pump. Thus the 'TAT)C '+CT) )%T is the vertical distance in feet from the centerline centerline of the pump to the free level of the liquid to be pumped.
Fig. 2-a Suction Lift S!o"ing Static Heads in a Pumping S#stem $!ere t!e Pump is Located %&ove t!e Suction 'an(. )Static Suction Head* '+CT) /0A1 exists when the source of supply is above the centerline of the pump. Thus the 'TAT)C '+CT) /0A1 is the vertical distance in feet from the centerline of the pump to the free level of the liquid to be pumped.
Fig. 2-& Suction Head S!o"ing Static Heads in a Pumping S#stem $!ere t!e Pump is Located +elo" t!e Suction 'an(. )Static Suction Head*
Section A -- Centrifugal Pump Fundamentals A-2 Capacity Capacity 234 is normally expressed in gallons pe r minute 2gpm4. 'ince liquids are essentially incompressible, there is a direct relationship between the capacity in a pipe and the velocity of flow. This relationship is as follows
(here A ! area of pipe pipe or conduit in square square feet. " ! velocity of flow in feet per second. 3 ! Capacity in gallons per minute NO!" n NO!" n vertical pumps the correction should be made to the eye of the suction or lowest impeller. Section A -- Centrifugal Pump Fundamentals A-3 Power and Efficiency Efficiency The work performed by a pump is a function of the total head and the weight of the liquid pumped in a given time period. The pump capacity in gpm and the liquid specific gravity are normally used in the formulas rather than the actual weight of the liquid pumped. 5ump input or brake horsepower 2bhp4 is the actual horsepower delivered to the pump shaft. 5ump output or hydraulic horsepower 2whp4 is the liquid horsepower delivered by the pump. These two terms are defined by the following formulas.
The constant #678 is obtained by dividing the number or foot pounds for one horsepower 2##,8884 by the weight of one gallon of water 29.## pounds.4 The brake horsepower or input to a pump is greater than the hydraulic horsepower or output due to the mechanical and hydraulic losses incurred in the pump. Therefore the pump efficiency is the ratio of these two values.
Section A -- Centrifugal Pump Fundamentals A-4 Specific Specific Speed and Pump Type Type 'pecific speed 2s4 is a non-dimensional design index used to classify pump impellers as to their type and proportions. )t is defined as the speed in revolutions per minute at which a geometrically similar impeller would operate if it were of such a si:e as to deliver one gallon per minute against one foot head. The understanding of this definition is of design engineering significance only, however, and specific speed should be thought of only as an index used to predict certain pump characteristics. The following following formula is used to determine specific speed
(here ! 5ump speed in ;5< 3 ! Capacity in gpm at the best efficiency point / ! Total head per stage at the best efficiency point The specific speed determines the general shape or class of the impeller as depicted in %ig. #. As the specific speed increases, the ratio of the impeller outlet diameter, 1$, to the inlet or eye diameter, 1i, decreases. This ratio becomes *.8 for a true axial flow impeller. ;adial flow impellers develop head principally through centrifugal force. 5umps of higher specific speeds develop head partly by centrifugal force and partly by axial force. A higher specific speed indicates a pump design with head generation more by axial forces and less by centrifugal forces. An axial flow or propeller pump with a specific speed of *8,888 or greater generates it=s head exclusively through axial forces. ;adial impellers are generally low flow high head designs whereas axial flow impellers are high flow low head designs.
"alues of 'pecific 'peed, s
Fig. , Impeller Design vs Specific Speed Section A -- Centrifugal Pump Fundamentals A-5 Net Positie Positie Suction Suction Head !NPSH" !NPSH" and Caitation The /ydraulic )nstitute defines 5'/ as the total suction head in feet absolute, determined at the suction no::le and corrected to datum, less the vapor pressure of the liquid in feet absolute. 'imply stated, it is an analysis of energy conditions on the suction side of a pump to determine if the liquid will vapori:e at the lowest pressure point in the pump. The pressure which a liquid exerts on its surroundings is d ependent upon its temperature. This pressure, called vapor pressure, is a unique characteristic of every fluid and increased with increasing temperature. (hen the vapor pressure within the fluid reaches the pressure of the surrounding medium, the fluid begins to vapori:e or boil. The temperature at which this vapori:ation occurs will decrease as the pressure of the surrounding medium decreases. A liquid increases increases greatly in volume volume when it vapori:es. vapori:es. ne cubic foot foot of water at room temperature temperature becomes *>88 cu. ft. of vapor at the same temperature. )t is obvious from the above that if we are to pump a fluid effectively, we must keep it in liquid form. 5'/ 5'/ is simply a measure of the amount of suction head present to prevent this vapori:ation at the lowest pressure point in the pump. 5'/ ;equired is a function of the pump design. As the liquid passes from the pump suction to the eye of the impeller, the velocity increases and the pressure decreases. There are also pressure losses due to shock and turbulence as the liquid strikes the impeller. The centrifugal force of the impeller vanes further increases the velocity and decreases the pressure of the liquid. The 5'/ ;equired is the positive head in feet absolute required at the pump suction to overcome these pressure drops in the pump and maintain the ma?ority of the liquid above its vapor pressure. The 5'/ ;equired varies with speed and capacity within any particular pump. 5ump manufacturer=s curves normally provide this information. Section A -- Centrifugal Pump Fundamentals A-# NPSH and Suction Suction Specific Speed )n designing a pumping system, it is essential to provide adequate 5'/ available for proper pump operation. )nsufficient 5'/ available available may seriously restrict pump selection, or even force an expensive system redesign. n the other hand, p roviding excessive 5'/ available may needlessly increase system cost. 'uction specific speed may provide help in this situation. 'uction specific speed 2'4 is defined as
(here ! 5ump speed ;5< @5< ! 5ump flow at best efficiency point at impeller inlet 2for double suction impellers divide total pump flow by two4. 5'/; ! 5ump 5'/ required at best efficiency point. %or a given pump, the suction specific speed is generally a constant - it does not change when the pump speed is changed. 0xperience has shown that 6888 is a reasonable value of suction specific speed. 5umps with a minimum suction specific speed of 6888 are readily available, and are not normally sub?ect to severe operating restrictions, unless the pump speed pushes the pump into high or very high suction energy.
An e#ample" %low $,888 @5< head 788 ft. (hat 5'/ A will be requiredB Assume at 788 ft., ft., #88 ;5< operation will be be required.
A related problem problem is in selecting selecting a new pump, especially especially at higher flow, for an existing system. 'uction specific speed will highlight applications where 5'/A may restrict pump selection. An example 0xisting system %low $888 @5< head 788 ft. 5'/A #8 ft. 'pecific @ravity *.8 'uction o::le 7 in. - (hat is the maximum speed at which a pump can be run without exceeding 5'/ availableB 25'/
# x *8 74
;unning a pump at this speed would require a gear and at this speed, the pump might not develop the required head. At a mini-mum, existing 5'/ A is constraining pump selection. 'ame system as *. )s a double suction pump practicalB %or a double suction pump 1e ! .> x 7E ! F. '.0. ! F. x #8 x 6888 x *.8 '.0. ! *#7 x *8 7 2/igh '.0.4 %or a double suction pump, flow is divided by two.
+sing a double suction pump is one way of meeting system 5'/ and obtaining a higher head. The amount of energy in a pumped fluid, that flashes into vapor and then collapses back to a liquid in the higher pressure area of the impeller inlet, determines the extent of the noise and&or damage from cavitation. 'uction 0nergy is defined as Suction !nerg$ % D e # N # S # Sg Where D e % &mpeller e$e diameter 'inches( Sg % Specific gravit$ of li)uid 'Sg - *+, for cold ater( /igh 'uction 0nergy starts at *78 x *8 7 for end suctabtion pumps and *$8 x *8 7 for hori:ontal split case pumps. "ery high suction energy starts at *. times the /igh 'uction 0nergy values. %or estimating purposes you can normally assume that the impeller eye diameter is approximately 68G of the suction no::le si:e, for an end suction pump, and >G of the suction si:e for a double suction split case pump. According to the the /ydraulic )nstitute, )nstitute, ans 5'/ 5'/ margin is required required above the 5'/ 5'/ ; of the pump to supress incipient cavitation. The amount of margin is a function of 'uction 0nergy and the critical nature of the application as follows 'uctio 'uction n 0ner 0nergy gy 5'/ 5'/
*.* - *.#
/igh
*.$ - *.>
"ery /igh
*.> - $.
'uction specific speed 6,888, pump speed #8 ;5<, suction no::le si:e 7 inch, specific gravity *.8, and the pump type is end suction. De . +/ # 01 % 2+31 Suction !nerg$ % D e # N # S # Sg % 2+3 # 422, # /5,,, # *+, % *64 # *,0 'ince *># x *8 7 H *78 x *87 , this is a /igh 'uction 0nergy pump.
Section A -- Centrifugal Pump Fundamentals A-$ Pump C%aracteristic Cures The performance of a centrifugal pump can be shown g raphically on a characteristic curve. A typical characteristic curve shows the total dynamic head, brake horsepower, efficiency, and net positive 'uction head all plotted over the capacity range of the pump. %igures , 7, I > are non-dimensional curves which indicate the general shape of the characteristic curves for the various types of pumps. They show the head, brake horsepower, and efficiency plotted as a percent of their values at the design or best efficiency point of the pump. %ig. below shows that the head curve for a radial flow pump is relatively flat and that the head decreases gradually as the flow increases. ote that the brake horsepower increases gradually over the flow range with the maximum normally at the point of maximum flow.
Fig. adial Flo" Pump below. The head curve for a mixed flow pump is steeper than for a radial flow pump. The shut-off head is usually *8G to $88G of the design head, The brake horsepower remains fairly constant over the flow range. %or a typical axial flow pump, the head and brake horsepower both increase drastically near shutoff as shown in %ig. >.
Fig. / 0ied Flo" Pump
Fig. %ial Flo" Pump The distinction between the above three classes is not absolute, and there are many pumps with characteristics falling somewhere between the three. %or instance, the %rancis vane impeller would have a characteristic between the radial and mixed flow classes.
Fig. 3 4omposite Performance 4urve
Section A -- Centrifugal Pump Fundamentals A-& Affinity Affinity 'aws The affinity laws express the mathematical relationship between the several variables involved in pump performance. They apply to all types of centrifugal and axial flow pumps. They are as follows *. (ith impeller diameter 1 held constant (here 3 ! Capacity, @5< / ! Total /ead, %eet J/5 ! Jrake /orsepower ! 5ump 'peed, ;5<
$.
(ith speed held constant
(hen the performance 23*, /*, I J/5 *4 is known at some particular speed 2 *4 or diameter 21*4, the formulas can be used to estimate the performance 23$, /$, I J/5$4 at some other speed 2 $4 or diameter 21 $4. The efficiency remains nearly constant for speed changes and for small changes in impeller diameter. !#ample" To illustrate the use of these laws, refer to %ig. 9 below. )t shows the performance of a particular pump at *>8 ;5< with various impeller diameters. This performance data has been determined by actual tests by the manufacturer. ow assume that you have a *#E maximum diameter impeller, but you want to belt drive the pump at $888 ;5<.
Fig. 3 4omposite Performance 4urve The affinity laws listed under * above will be used to determine the new performance, with * *>8 ;5< and $ ! $888 ;5<. The first step is to read the capacity, head, and horsepower at several points on the * #E dia. curve in %ig. 6 below. %or example, one point may be near the best e fficiency point where the capacity is #88 @5<, the head is *78 ft, and the J/5 is approx. $8 hp.
This will then be the best efficiency point on the new $888 ;5< curve. Jy performing the same calculations for several other points on the *>8 ;5< curve, a new curve can be drawn which will approximate the pump=s performance at $888 ;5<, %ig. 6. Trial and error would be required to solve this problem in reverse. )n other words, assume you want to determine the speed required to make a rating of #F# @5< at a head of $86 ft. Kou would begin by selecting a trial speed and applying the affinity laws to convert the desired rating to the corresponding rating at *>8 ;5<. (hen you arrive at the correct speed, $888 ;5< in this case, the corresponding *>8 ;5< rating will fall on the *#E diameter curve.
Fig. 5
Section A -- Centrifugal Pump Fundamentals A-( System Cures Cures %or a specified impeller diameter and speed, a centrifugal pump has a fixed and predictable performance curve. The point where the pump operates on its curve is dependent upon the characteristics of the system )n which it is operating, commonly called the 'ystem /ead Curve. ..or, the relationship between flow and hydraulic losses7 in a system. This representation is in a graphic form and, since friction losses vary as a square of the flow rate, the system curve is parabolic in shape.
*. $.
Jy plotting the system head curve and pump curve together, it can be determined (here the pump will operate on its curve. (hat (hat chan change ges s wil willl occ occur ur if the the sys syste tem m hea head d cur curve ve or the the pum pump p per perfo form rman ance ce curv curve e cha chang nges es.. 'TAT)C /0A1 - A %;)CT) As the levels in in the suction and discharge discharge are the same 2%ig. *4, there there is no static head head and, therefore, the the system curve starts at :ero flow and :ero head and its shape is determined solely from pipeline losses. The point of operation is at the intersection of the system head curve and the pump curve. The flow rate may be reduced by throttling valve.
Fig.1 6o Static Head %ll Friction 5')T)"0 'TAT)C /0A1 The parabolic shape of the system curve is again determined by the friction losses through the system including all bends and valves. Jut in this case there is a positive static head involved. This static head does not affect the shape of the system curve or its EsteepnessE, but it does dictate the head of the system curve at :ero flow rate.
The operating point is at the intersection of the system curve and pump curve. Again, the flow rate can be reduced by throttling the discharge valve.
Fig. 2 Positive Suction Head 0@AT)"0 2@;A")TK4 /0A1 )n the illustration below, a certain flow rate will occur by gravity head alone. Jut to obtain higher flows, a p ump )s required to overcome the pipe friction losses in excess of E/E - the head of the suction above the level of the discharge. )n other words, the system curve is plotted exactly as for any other case involving a static head and friction head, except the static head is now negative. The system curve begins at a negative value and shows the limited flow rate obtained by gravity alone.
Fig. , 6egative )Gravit#* Head <'TK )%T- )TT0 %;)CT) /0A1 The system head curve in the illustration below starts at the static head E/E and :ero flow. 'ince the friction losses are relatively small 2possibly due to the large diameter pipe4, the system curve is EflatE. )n this case. the p ump is required to overcome the comparatively large static head before it will deliver any flow at all.
Fig. 7 0ostl# Lift - Little Fricition Head
L/ydraulic losses in piping systems are composed of pipe friction losses, valves, elbows and o ther fittings, entrance and exit losse 2these to the entrance and exit to and from the pipeline normally at the beginning and end not the pump4 and losses from changes in pipe si:e by enlargement or reduction in diameter.
Section A -- Centrifugal Pump Fundamentals Formulas
S$m8ols
@5< ! gallons per minute C%' ! cubic feet per second b. ! pounds /r. ! hours JJ ! barrel 2F$ gallons4 'p.@r. ! specific gravity / ! head in feet psi ! pounds per square inch )n. /g. ! inches of mercury hv ! velocity head in feet " ! velocity in feet per second g ! #$.*7 ft&sec $ 2acceleration of gravity4 A ! area in square inches ).1. ! inside diameter in inches J/5 ! brake horsepower 0ff. ! pump efficiency expressed as a decimal s ! specific speed ! speed in revolutions per minute v ! peripheral velocity of an impeller in feet per second 1 ! )mpeller in inches c ! critical speed f ! shaft deflection in inches 5 ! total force in pounds ! bearing span in inches m ! constant usually between F9 and > for pump shafts 0 ! modules of elasticity, psi - $> to #8 million for steel
L'00 SO9&DS AND S9:;;&!S %; '+;;K %;<+A' 'ection J -- 5ump Application 1ata +-2 0aterial Selection 4!art This chart is intended as a guide in the selection of economical materials. )t must be kept in mind that corrosion rates may vary widely with tem-perature, concentration, and the presence of trace elements or abrasive solids. Jlank spaces in the chart indicate a lack of accurate corrosion data for those specific conditions. )n g eneral, the chart is limited to metals and non-metals regularly furnished by )TT-@oulds. Note"
;ecommended
J
+seful resistance
M
+nsuitable
'teel
Carbon st steel, ca cast ir iron an and du ductile ir iron
Jr:
Carbon steel, cast iron and ductile iron
#*7
'tainless steel
A-$8 C1F
Carpenter stainless C1F
Alloy $$8
$$8 Alloy $$8 stainless stainless steel
Alloy $$8
Alloy $$8 stainless stainless steel
C-$>7
(rought /astelloy B C-$>7 alloy
Ti
Titanium unalloyed
0T%0
0thylenetetrafluoro-ethylene 0thylenetetrafluoro-ethylene 2Tef:el B 4 %5 %luoropolymers 2e.g.,Teflon B 4 including perfluoroalkoxy 25%A4, polytetrafluoroethylene polytetrafluoroethylene 25T%04 and fluorinated ethylene propylene 2%054
%;5
%iber-reinforced plastic 2vinylester resin4
051<
0thylenepropylene rubber 2ordel B 4
%N<* %N<*
'tan 'tanda dard rd gra grade des s dip dipol olym ymer ers s of hexa hexafl fluo uoro ropr prop opyl ylen ene e 2/%5 2/%544 and and viny vinyli lide dene ne flu fluor orid ide e 2"% 2"% $ 4 2"it 2"iton on B 4
%N<$
'pecialty grades terpolymerscomprising terpolymerscomprising at least three of the following /%5, "%$ , tetrafluorethylene 2T%04, perfluoromethylvinyl ether 25<"04 or ethylene 204. 'pecialty grades may have significantly improved chemical compatibility compared to standard grades in many harsh chemical environments 2"iton B 4.
%%N<
Copolymer of T%0 and 5<"0 2Nalre: B 4
5"1%
5oly olyvinylidene fluori oride 2Nynar B , 'olef B 4
* Compatibility is dependent on specific freon. Contact elastomer manufacturer. a8le * a8le < a8le 4
a8le 3 Section = -- Pump Application Data
=-*5<54 )-3 Pipin* +esi*n The design of a piping system can have an important effect on the successful operation of a centrifugal pump. 'uch items as sump design, suction piping design, suction and discharge pipe si:e, and pipe supports must all be carefully considered. 'election of the discharge pipe si:e is primarily a matter of economics. The cost of the various pipe si:es must be compared to the pump si:e and power cost required to overcome the resulting friction head. The suction piping si:e and design is far more important.
Fig 1 %ir Poc(ets in Suction Piping )f an elbow is required at the suction of a double suction pump, it should be in a vertical position if at all possible. (here it is necessary for some reason to use a hori:ontal elbow, it should be a long radius elbow and there should be a minimum of three diameters of straight pipe between the elbow and the pump as shown in %ig $ for low suction energy pumps, and five pipe diameters for high suction energy pumps. %ig # shows the eftect of an elbow directly on the suction. The liquid will flow toward the outside of the elbow and result in an uneven flow distribution into the two inlets of the double suction impeller. oise and excessive axial thrust will result.
Fig. 2 8l&o"s %t Pump Suction
Fig. , 8ffect of 8l&o" Directl# on Suction
Section = -- Pump Application Data )-4A Sea,in* The proper selection of a seal is critical to the success of every pump application. %or maximum pump reliability, choices must be made between the type of seal and the seal environment. )n addition, a sealless pump is an alternative, which would eliminate the need for a dynamic type seal entirely. Sealing =asics There are two basic kinds of seals static and dynamic. 'tatic seals are employed where no movement occurs at the Ouncture to be sealed. @askets and -rings are typical static seals. 1ynamic seals are used where surfaces move relative to one another. 1ynamic seals are used, for example, where a rotating shaft transmits power through the wall of a tank 2%ig. *4, through the casing of a pump 2%ig. $4, or through the housing of other rotating equipment such as a filter or screen.
Fig. 1 4ross Section of 'an( and 0ier
Fig. 2 '#pical 4entrifugal Pump A common application application of sealing devices devices is to seal the rotating shaft of a centrifugal pump. To best understand understand how such a seal functions a quick review of pump fundamentals is in order. )n a centrifugal pump, the liquid e nters the suction of the pump at the center 2eye4 of the rotating impeller 2%igures # and F4.
Fig. , 4entrifugal Pump9 Liguid 8nd
Fig. 7 Fluid Flo" in 4entrifugal Pump As the impeller impeller vanes rotate, they they transmit motion motion to the incoming incoming product, which which then leaves the impeller, impeller, collects in the pump casing, and leaves the pump under pressure through the pump discharge. 1ischarge pressure will force some product down behind the impeller to the drive shaft, where it attempts to escape along the rotating drive shaft. 5ump manufacturers use various design techniques to reduce the pressure of the product trying to escape. 'uch techniques include *4 the addition of balance holes through the impeller to permit most of the pressure to escape into the suction side of the impeller, or $4 the addition of back pump-out vanes on the back side of the impeller. /owever, as there is no way to eliminate this pressure completely, sealing devices are necessary to limit the escape of the product to the atmosphere. 'uch sealing devices are typically either compression packing or endface mechanical seals.
Section = -- Pump Application Data )-4) a*netic +rie Pumps &N;OD:C&ON 0nvironmental concerns and recurring mechanical seal problems have created a need for sealless pumps in the chemical and petrochemical industries. )n some cases, more stringent regulations by the 05A, '/A and local agencies are mandating the use of sealless pumps. ne type of sealless pump is the magnetic drive pump which uses a permanent magnetic coupling to transmit torque to the impeller without the need for a mechanical seal for packing. P;&NC&P9!S OF OP!;A&ON
o $pes of >agnetic Drive Pump A+ ;otating Driven Shaft This type of design typically uses metal components and is be st suited for heavy duty applications. The metallic construction offers the best strength, temperature and pressure capability required for heavy duty applications.
Corrosion resistant high alloy materials such as #*7'', /astelloy, and Alloy $8 are offered. The rotating shaft does, however, increase the number of parts required and thus increases the complexity and cost of the pump. This type of design typically uses a pressuri:ed recirculation circuit, which helps prevent vapori:ation of liquid required for process lubricated bearings. 2;efer to ethods A. +etermination +etermination of tota, %ead The total head of a pump can be determined by gauge readings as illustrated in %ig. *.
%ig * 1etermination of Total /ead from @uage ;eadings Negative Suction Pressure" T1/ ! 1ischarge gauge reading converted to feet of liquid P vacuum gauge reading converted to feet of liquid P distance between point of attachment of vacuum gauge and the centerline of the discharge
Positive Suction Pressure" or T1/!1ischarge gauge reading converted to feet of liquid-pressure gauge reading in suction line converted to ft. of liquid P distance between center of discharge and suction gauges, h, in feet
)n using gauges when the pressure is positive or above atmos-pheric pressure, any air in the gauge line should be vented off by loosening the gauge until liquid appears. This assures that the entire gauge line is filled with liquid and thus the gauge will read the pressure at the elevation of the centerline of the gauge. /owever, the gauge line will be empty of liquid when measuring vacuum and the gauge will read the vacuum at the elevation of the point of attachment of the gauge line to the pipe line. These assumptions are reflected in the above definitions. The final term in the above definitions accounts for a difference in si:e between the suction and discharge lines. The discharge line is normally smaller than the suction line and thus the dis-charge velocity is higher. A higher velocity results in a lower pressure since the sum of the pressure head and velocity head in any flowing liquid remains constant. Thus, when the suction and discharge line si:es at the gauge attachment points are different, the resulting difference in velocity head must be in-cluded in the total head calculation.
%ig. $
%ig. #
Section = -- Pump Application Data )-1 Corrosion / ateria,s of Construction 'electing the right pump type and si:ing it correctly are critical to the success of any pump application. 0qually important is the selection of materials of construction. Choices must be made between metals and&or non-metals for pump components that come into contact with the pumpage. )n a ddition, gaskets and -ring material selections must be made to assure long leak-free operation of the pump=s dynamic and static sealing ?oints. To assist in proper selection, included in this section is a brief discussion of specific types of corrosion and a general material selection guide. Corrosion Corrosion is the destructive attack of a metal by chemical or electra-chemical reaction with its environment. )t is important to understand the various types of corrosion and factors affecting corrosion rate to properly select materials. ':P8S ;F 4;;SI;6 *. @alvanic corrosion corrosion is the electro-chemical electro-chemical action action produced when one metal is is in electrical contact with with another more noble metal, with both being immersed in the same corroding medium called the electrolyte. A galvanic cell is formed and current flows between the two materials. The least noble material called the anode will corrode while the more noble cathode will be protected. )t is important that the smaller wearing parts in a pump be of a more noble material than the larger more massive parts, as in an iron pump with bron:e or stainless steel trim. %ollowing is a galvanic series listing the more common metals and alloys. Section = -- Pump Application Data *+ DA:> O; ?;AD! ?;AD! - The elevation of the surface from which the pump is supported. <+ SA&C 9&@:&D 9!V!9 - The vertical distance from grade to the liquid level when no liquid is being drawn from the well or source. 4+ D;AWDOWN D;AWDOWN - The distance between the static liquid level and the liquid level when pumping at required capacity. 3+ P:>P&N? 9&@:&D 9!V!9 9!V!9 - The vertical distance from grade to liquid level when pumping at rated cap-acity. 5umping liquid level equals static water level plus drawdown. 2+ S!&N? S!&N? - The distance from grade to the top of the pump bowl assembly. 0+ P9 'OA9 P:>P 9!N?H( - The distance from grade to lowest point of pump. 6+ ;A!D P:>P H!AD H!AD - ift below discharge plus head above discharge plus friction losses in discharge line. This is the head for which the customer is responsible and does not include any losses within the pump. + CO9:>N AND D&SCHA;?! H!AD F;&C&ON 9OSS - /ead loss in the pump due to friction in the column assembly and discharge head. %riction loss is measured in feet and is dependent upon column si:e, shaft si:e, setting, and discharge head si:e. "alues given in appropriate charts in 1ata 'ection. /+ =OW9 H!AD H!AD - Total head which the pump bowl assembly will deliver at the rated capacity. This is curve performance. *,+ =OW9 !FF&C&!NCB!FF&C&!NCB - The efficiency of the bowl unit only. This value is read directly from the performance curve.
**+ =OW9 HO;S!POW!;HO;S!POW!; - The horsepower - required by the bowls only to deliver a specified capacity against bowl head.
*<+ OA9 P:>P H!AD H!AD - ;ated pump head plus column and discharge head loss. ote This is new or final bowl head. *4+ SHAF F;&C&ON 9OSS - The horsepower required to turn the lineshaft in the bearings. These values are given in appropriate table in 1ata 'ection. *3+ P:>P =;A! HO;S!POW!; HO;S!POW!; - 'um of =bowl horsepower plus shaft loss 2and the driver thrust bearing loss under certain conditions4. *2+ OA9 P:>P !FF&C&!NCB 'WA!; O WA!;( -The efficiency of the complete pump less.the driver, with all pump losses taken into account.
*0+ OV!;A99 !FF&C&!NCB 'W&;! O WA!;( -The efficiency of the pump and motor complete. verall efficiency ! total pump efficiency M motor efficiency. *6+ S:=>!;?!NC!-1istance S:=>!;?!NC! -1istance from liquid level to suction bell.
Section = -- Self-Priming Pump S$stem ?uidelines 'elf-priming 'elf-priming pumps are inherently designed to allow the pump to re-prime itself typically under lift conditions. These pumps are very effective to the end user in that they will eliminate the need for foot valves, vacuum and e?ector pumps which can become clogged or be impractical to use for prolonged or remote operation. Although the pump itself is designed to accomplish this task, it )s important to understand the principle of how self-priming is achieved so that the piping system can be designed so as not to conflict with this function. A self-priming self-priming pump, by definition, definition, is a pump pump which will clear its passages of air if it becomes becomes air bound and resume delivery of the pumpage without outside attention. To accomplish this, a charge of li)uid sufficient to prime the pump must 8e retained in the casing 'See Fig+ A( or in an accessor$ priming cham8er+ (hen the pump starts, the rotating impeller creates a partial vacuum air from the suction piping is then drawn into this vacuum and is entrained in the liquid drawn from the priming chamber. This air-liquid mixture is then pumped into the air separation chamber 2within the casing4 where the air is separated from the liquid with the air being e#pelled out the discharge piping 2%ig. J4 and the liquid returning to the priming chamber. This cycle is
repeated until all of the air from the suction piping has been expelled and replaced by pumpage and the prime has been established 2%ig. C4.
%ig. A
%ig. J & %ig. C The following considerations should be made when designing a piping system for which a self-priming pump is to be used B Care should be exercised to insure that adequate liquid is retained )n the p riming chamber. %or outdoor&remote installations a heating element may be required to prevent free:ing. %or dirty services a strainer may be required to keep solids from accumulating in the priming chamber, thus displacing priming liquid. B The static lift and suction piping should be minimi:ed to keep priming time to a minimum. 0xcessive priming time can cause liquid in the priming chamber to vapori:e before prime is achieved. B All connections in the suction piping should be leak-free as air could be sucked in, thus extending&compromising priming of the pump. 25umps sealed with p acking should be flushed to prevent air from being introduced.4 B A priming bypass line 2'ee %ig. 14 should be installed so that back pressure is not created in the discharge piping during priming which would prevent the pump from priming )tself. 2'elf-priming 2'elf-priming pumps are not good air compressorsQ4 B The suction piping should be designed such that no high points are created where air can be trapped&accumulate which can prevent priming. /istorically this has been problematic on top unloading of rail cars. 2'ee %ig. 04
%ig. 1
%ig. 0 Tank Car +nloading Section = -- Priming ime Calculations 5riming time data for each 67 pump si:e and speed is displayed on the individual performance curves where priming time is plotted versus effective static lift for maximum, minimum and intermediate )mpeller diameters. This data is for suction piping of the same nominal diameter as the pump suction, i.e. #E piping and #E pump suction, and must be corrected for suction pipe diameters different from the pump suction and for suction pipe lengths greater than the effective static lift. To calculate the total priming time for a given system *. 'elect the correct si:e and speed pump from the performance curve for the given rating. $. Calculate the NPSH Availa8le for Availa8le for the system. The available 5'/ must be e)ual to or greater than the NPSH ;e)uired by ;e)uired by the selected pump at the rating point. 5'/ A ! 5-2 s P "p P hf 4 where 5 ! 5ressure on surface of liquid in feet absolute s !
where 5TT ! Total system priming time. 5T0' ! 5riming time in seconds for the effective static lift 2'tep F.4 '5 ! Total suction pipe length above the free surface of the liquid in feet. es ! 0ffective static lift. 1p ! ominal pipe diameter. 1s ! ominal pump su ction diameter.
Section ! -- Paper Stoc E-4 Pump Types 0sed in t%e Pu,p and Paper ndustry Pump $pes :sed in the Pulp and Paper &ndustr$ Chart
Section & -- Pump Operation and >aintenance -4 Trou,e s%ootin* Centrifu*a, Pumps rou8le shooting Centrifugal Pumps Chart *
Section & -- Pump Operation and >aintenance -5 Arasie S,urries and Pump ear The rate of wear is directly influenced by the system p oint on the characteristic curve. These condition points can be divided into four significant :ones of operation 2%ig. *4.
Overcapacit$ Eone" The velocities within the pump are usually very high and recirculation occurs causing excessive wear. The radial hydraulic loads on the impeller increase. ;ecommended Operation Eone" The velocities within the pump are reduced 2but not enough to cause settlement4. ;ecirculation is minimal and the flow in the suction no::le should be axial 2no induced vortex4. The radial hydraulic loads are minimi:ed. ;educed capacit$ Eone" The velocities within the pump are low, separation and recalculation occurs, causing excessive wear. ;educing the capacity should be limited because a certain minimum velocity must be maintained to avoid settling out with the consequence of increased wear and clogging. The hydraulic radial loads will increase and the pump efficiency will decrease. Shut Valve Eone" This is the point of :ero flow, and pump should not be o perated at this point for any length of time. (ear and tear will be rapid due to separation and recirculation, the hydraulic forces will be at their highest, and settlement and plugging will occur. The pump will rapidly heat up, which is particularly serious in rubber constructed pumps. P;&NC&PA9 W!A; A;!AS As the abrasive mixture passes through through the pump, all the wetted surfaces surfaces which come in contact contact will be sub?ect to varying degrees of wear. )t is very important to note that the performance of a conventional centrifugal pump, which has been misapplied to a slurry service, will be significantly effected by a relatively small degree of abrasive wear. The areas most prone to wear, in order of severity, are *. 'uction sideplate, particularly at the no::le region. $. )mpeller, particularly at the eye vane inlets, suction side impeller shroud, and the vane tips. #. Casing cutwater and side walls ad?acent to the impeller tip. F. 'tuffing box packing and sleeve. NO!" )n NO!" )n the case of a conventional pump with radial wear rings on the impeller, this is where the worst wear occurs. n severely abrasive services where there are high concentrations of hard, larger, sharp particles, the suction side liner life can be increased if it is rotated periodically to equali:e the effects of wear. )n hard iron pumps applied to severely abrasive service, the relative wear rates of the suction side liner, casing, and impeller are in the order of # to *. to *, e.g. the life of the casing is three times that of a suction side wear plate. ;ecogni:ing that due to the nature of the mixtures being pumped, the complete elimination of wear is impossible, the life of the parts can be appreciably prolonged and the cost of maintenance reduced by a good pump design and selection, e.g. B Construct the pump with good abrasion resistant materials.
B 5rovide generous wear allowances on all parts sub?ect to excessive wear. B Adopt a hydraulic design which will minimi:e the effects causing wear. B Adopt a mechanical design which is suitable for the materials of construction and has ready access to the parts for renewal. B imit the head to be generated and select a low speed pump.
Section & -- Pump Operation and >aintenance -12 ie,d A,i*nment 5roper field alignment of pumps and d rivers is critical to the life of the equipment. There are three methods used in industry rim and face, reverse dial indicator, and laser alignment. ;&> AND FAC! This method should not be used when there is no fixed thrust bearing or on pumps&drivers that have axial shaft movement.
9AS!; A9&?N>!N Although a popular method, it=s not any more accurate than than either dial indicator indicator method. )nstruments are expensive and require frequent calibration. ;!V!;S! D&A9 &ND&CAO; This method is the most widely used and is recommended for most situations.
>!CHAN&CA9 A9&?N>!N P;OC!D:;! This procedure assumes the presenter knows how to align a pump and has a basic understanding of pump baseplates and piping installation. There are many a lignment systems available. (e will be using the plotting board with dial indicators developed by <.@. !N A. Jaseplate )nspection )nspection *. )nspect all mounting surfaces to make sure they are dean and free of any paint, rust, grime, burrs, etc. a. Thoroughly clean mounting surfaces. 1ebar using a honing stone if necessary. b. At this point, it is assumed that the baseplate has been installed correctly and is level. J. 5ump and 1river )nspection *. )nspect all mounting surfaces to make sure they are clean and free of any paint, rust, grime, burrs, etc. C. 'him )n9pect)an *. )nspect all shims to make sure they are clean and free of any paint, rust, grime, burrs. etc. $. 1imensionally inspect A shims to be used and record the reading on the individual shims. 1 T A''+<0 T/AT T/0 '/)<' A;0 T T/0 0MACT 1)<0')' T/ATA;0 ;0C;101 T/0<.
Section & -- Pump Operation and >aintenance -11 Predictie and Preentatie aintenance aintenance Pro*ram This overview of 5redictive and 5reventative P P!;FO;>ANC! >ON&O;&N? There are six parameters that should be monitored to understand how a pump is performing. They are 'uction pressure 25s 4, discharge pressure 25d4, flow 234, pump speed 2 r 4, 4, pumpage properties, and power. 5ower is easiest measured with a clip on amp meter but some facilities have continuous monitoring systems that can be utili:ed. )n any event, the intent is to determine the J/5 of the pump. (hen using a clip on amp meter the degree of accuracy is limited. )t should not be used to determine the efficiency of the pump. Clip on amp meters are best used for trouble shooting where the engineer is trying to determine the operating point of the pump. The most basic method of determining the T1/ of the pump is by utili:ing suction and discharge gauges to determine 5' and 5d. The installation of the taps for the gauges is very important. )deally, they should be located normal to the pipe wall and on the hori:ontal centerline of the pipe. They should also be in a straight section of pipe. Avoid locating the taps in elbows or reducers because the readings will not indicate the true static pressure
due to the velocity head component. Avoid locating taps in the top or bottom of the pipe because the gauges can become air bound or clogged with solids. %low measurements can be difficult to obtain but every effort should be made to do so, especially when trouble shooting. )n some new installations permanent flow meters are installed which make the lob easier. (hen this is the case, make sure the flow meters are working properly and have been calibrated on a regular schedule. (hen flow meters are not installed, pitot tubes can be used. 5itot tubes provide a very accurate measure of flow, but this in an obtrusive device and provisions must be made to insert the tube into the piping. The other method of determining flow is with either a doppler or transitime device. Again, provisions must be made on the piping for these instruments, but these are non-obtrusive devices and are easier to use than the pitot tube. Caution must be exercised because each device must be calibrated, and independent testing has shown these devices are sensitive to the pumpage and are not *88G accurate.
Section & -- Pump Operation and >aintenance -1 mpe,,er C,earance &>P!99!; C9!A;ANC! pen impeller centrifugal pumps offer several advantages. They=re particularly suited but not restricted to liquids which contain abrasive solids. Abrasive wear on an open impeller is distributed over the diametrical area area swept by the vanes. The resulting total wear has less effect on performance than the same total wear concentrated on the radial ring clearance of a closed impeller. The open impeller permits restoration of Enew pumpE running clearance after wear has occurred without parts replacement. P!99!; C9!A;ANC! 'D&A9 &ND&CAO; >!HOD( *. After locking out power, remove coupling guard and coupling. $. 'et dial indicator so that button contacts shaft end. #. oosen ?am nuts 2F$#J4 on ?ack bolts 2#>* A4 and back bolts out about two turns. F. Tighten each locking bolt 2#>8C4 evenly, drawing the bearing housing toward the bearing frame until impeller contacts casing. . 'et indicator to :ero and back locking bolt about one turn. 7. Thread ?ack bolts in until they evenly contact the bearing frame. Tighten evenly backing the bearing housing away from the frame until indicator shows the proper clearance established in instruction manual.L >. 0venly tighten locking bolts, the ?ack bolts keeping indicator at proper setting. 9. Check shaft for free turning. L0stablished clearance may vary due to service temperature.
Section & -- Pump Operation and >aintenance -( )a,, )earin*s - Hand,in*6 7ep,acement and aintenance Su**estions Jall bearings are carefully designed and made to watch-like tolerances. They give long, trouble-free service when property used. They wilt not stand abuse. !!P C9!AN 1irt causes 68G of early bearing failures. Cleanliness is a must when working on bearings. 'ome things which help *. 1o not open housings unless absolutely necessary. $. 'pread clean newspapers on work benches and at pump. 'et tools and bearings on papers o nly. #. (ash hands. (ipe dirt, chips and grease off tools. F. Neep bearings, housings, and shaft covered with clean cloths whenever they are not being worked on. . 1o not unwrap n ew bearings until ready to install. 7. %lush shaft and housing with clean solvent before reassembly. P:99 =!A;&N?S CA;!F:99B *. +se sleeve or puller which contacts ?ust inner race of bearing. 2The only exception to this is some double suction pumps which use the housing to pull the bearing.4 $. ever press against the balls or ball cages, only against the races. #. 1o not cock bearing. +se sleeve which is cut square, or puller which is ad?usted square. F. (hen using a bearing housing to pull a bearing, pull evenly, do not hammer on housing or shaft. (ith both races locked, shock will be carried to balls and ruin bearing. &NSP!C =!A;&N?S AND SHAF *. ook bearing over carefully. 'crap it if there are any flat spots, nicks or pits on the balls or races. Jearings should be in perfect shape. $. Turn bearing over slowly by hand. )t should turn smoothly and quietly. 'crap if EcatchyE or noisy. #. (henever in doubt about the condition of the bearing, scrap it. %ive or ten dollars worth of new bearings may prevent serious loss from downtime and pump damage. )n severe or critical services, replace bearings at each overhaul. F. Check condition of shaft. Jearing seats should be smooth and free from burrs. 'mooth burrs with crocus cloth. 'haft shoulders should be square and not run over. CH!C N!W =!A;&N?S Je sure bearing is of correct si:e and type. %or instance, an angular contact bearing which is dimensionally the same as a deep groove bearing may fit perfectly in the pump. /owever, the angular contact bearing is not suitable for end thrust in both directions, and may quickly fail. Also check to see that shields 2if any4 are the same as in the original unit. ;efer to the pump instruction manual for the proper bearing to use. u se. &NSA99 CA;!F:99B *. il bearing seat on shaft lightly. $. 'hielding, if any, must face in proper direction.
Section & -- Pump Operation and >aintenance -& 8eep Air 9ut of :our Pump 1->, 5umping iquids with 0ntrained @as. !S&N? FO; A&; &N C!N;&F:?A9 P:>PS The amount of air which can be handled with reasonable pump life varies from pump to pump. /owever, in no case is it expected that a pump wilt give better life with air p resent than it would if the liquid were entirely air-free. The elimination elimination of air has greatly improved the operation and life of
many troublesome pumps. (hen trouble occurs, it is common to suspect everything but air, and to consider air last, if at alt. )f air is present, the pump is likely to operate with a certain amount of internal noise. This noise can be described as a Egravel noiseE -sounds very much as though the pump were handling water full of gravel. This is the same type of noise generally associated with cavitation. )n many cases a great deal of time, inconvenience, and expense can be saved by making a simple test for the presence of air. (e will assume that calculations have already been made to assure that the 5'/ available is greater than that required by the pump, 2the noise is not a result of cavitation4. The next step should be to check for the presence of entrained air in the pumpage. (hen the source of suction supply is above the centerline of the pump, a check for air leaks can be made by collecting a sample in a Ebubble bottleE as illustrated. 'ince the pressure at the suction chamber of the pump is above atmospheric pressure, a valve can be installed in one of the tapped openings at the high point in the chamber and liquid can be fed into the Ebubble bottle.E The presence of air o r vapor will show itself in the Ebubble bottle.E This test can also be made from a high point in the discharge side. bviously, the next step is to eliminate the source of air since quantities present insufficient amount to be audible are almost certain to cause p remature mechanical failure. NO!" The NO!" The absence of bubbles is not p roof that the pumpage doesn=t contain air. Section & -- Pump Operation and >aintenance -# Start-0p and S%ut-9ff Procedure for Heated and 0n%eated a* +rie Pumps 'his procedure does not replace the operation &nstruction hand8oo+( A+ CH!C9&S =!FO;! SA;-:P *. The nominal motor power must not exceed the pump=s allowed maximum capacity 2compare rating plates of motor and pump4. $. Check direction of rotation with disconnected coupling. #. Check alignment of coupling. F. Check ease of pump operation by hand. . Attach coupling p rotection. 7. Connect thermocouples, dry run protection, pressure gauges, etc. >. Connect heater for heated pumps. 9. Connect cooling system 2if required4. 6. Attention )nsulation must not cover roller bearings. =+ SA;-:P *. 5reheat heated pumps for a minimum of $ hours. $. pen pressure valve. #. pen suction valve completely and fill pump. F. After $-# minutes close pressure valve. . )n case of external cooling, switch on coolant flow. 7. 'tart motor. >. 'ubsequently open pressure valve slowly until p ump reaches specified performance level. C+ SH:-OFF *. Close pressure valve. $. 'hut off motor. Allow pump to slow down smoothly. #. )n case of external cooling, shut off coolant flow. F. Close suction valve. NO!" B Throttling must not be done with the suction valve. B ever shut off the pump with the suction valve. B 5ump must never run dry. B ever run the pump against a closed pressure valve. B The pump motor unit must run vibration free. B Temperature of roller bearings must not exceed tolerated limit.
