PNEUMAT PNEUMATIC BRAKING SYSTEM A POJECT REPORT Submitted by
DEVANAND JHA (00113103611) SOURABH CHOUDHARY (04013103611) PRINCE KR. MISHRA (06013103611)
in partial fulfillment for the award of the degree of
BACHELOR OF TECHNOLOGY IN MECHANICAL AND AUTOMATION AUTOMATION ENGINEERING ENGI NEERING
GURU GOBIND SINGH INDRAPRASTHA UNIVERSITY DELHI (011 ! 01")
1
DECLARATION
We hereby declare that the project entitled “ P#$%&'* B+',#- S/$&” submitted by us in partial fulfillment of the requirement for the award of BACH BACHEL ELOR OR
OF
TECHN ECHNOL OLOG OGY Y
in
MECH MECHAN ANIC ICAL AL
AND
AUTOMATION ENGINEERING , comprises our original work and due
references have been made in text to all other material used
!ignature of the !tudent"s#$ %lace$ &ate$
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CERTIFICATE (his is to certify that the project entitled P#$%&'* B+',#- S/$& is the bonafide bonafide work carrie carried d out out by D$2'#'# D$2'#'# J'5 S%+'7 S%+'7 C%'+ C%'+5 5 P+#*$ ,+. M/+' student"s# of ) (ech, (ech, *uru *obind !ingh +ndraprastha
niversity &elhi, during the year '-11.'-1/ in partial fulfillment of the requirements for the award of the &egree of )achelor of (echnology and that the project has not formed the basis for the award of any degree earlier
!ignature of the *uide$ %lace$ &ate$
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ACKNO8LEDGEMENTS (he completion of any inter.disciplinary inter.disciplinary project depends upon cooperation, co.ordination and combined efforts of several sources of knowledge We are grateful to r !hiv 2umar "34& 56# for his even willingness to give us valuable advice and direction, whenever we approached him with a problem We are thankful to him for providing immense guidance for this project We are also thankful tor ukesh 2umar and rs (aran for their immense guiding in theoretical 5nalysis %art of our project We are also thankful to all faculty of !+( and *%76 to encourage us for completion completion of this project and providing us relevant data for completion of our project DEVANAND JHA (00113103611) SOURABH CHOUDHARY (04013103611) PRINCE KUMAR MISHRA (06013103611) B'*$9+ : T$*#9- # M$*'#*'9 '# A%&'# E#-#$$+#;S$& S$//# < 011!1"
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ABSTRACT
5n air brake is a conveyance braking system actuated by compressed air odern trains rely upon a fail.safe air brake system that is based upon a design patented by *eorge Westinghouse on arch /
19:' (he
Westinghouse 5ir )rake 7ompany "W5)74# was subsequently organi;ed to manufacture and sell Westinghouse
/
(5)>6 4= 74?(6?(! 1 +ntroduction to the (opic 5bout 5ir )rake 5bout &rum )rake 3istory ' Working 0 4peration of control valve 8 7omponent requirement / %roject &escription !afety system %neumatics &isc )rake !olenoid valve @ Aeferences
@
ABOUT AIR BRAKE
:
%iping diagram from 1B'- of a Westinghouse 6.( 5ir )rake system on a locomotive
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ABOUT DRUM BRAKE
5 drum brake is a brake in which the friction is caused by a set of shoes or pads that press against the inner surface of a rotating drum (he drum is connected to a rotating wheel
N+&'9 +%& 7+',$ ''*$ = : >'
B
HISTORY
(he modern automobile drum brake was invented in 1B-' by >ouis Aenault, though a less.sophisticated drum brake had been used by aybach a year earlier +n the first drum brakes, the shoes were mechanically operated with levers and rods or cables =rom the mid.1B0-s the shoes were operated with oil pressure in a small wheel cylinder and pistons "as in the picture#, though some vehicles continued with purely.mechanical systems for decades !ome designs have two wheel cylinders
(he shoes in drum brakes are subject to wear and the brakes needed to be adjusted regularly until the introduction of self adjusting drum brakes in the 1B/-s +n the 1B@-s and 1B:-s brake drums on the front wheels of cars were gradually replaced with disc brakes and now practically all cars use disc brakes on the front wheels, with many offering disc brakes on all wheels 3owever, drum brakes are still often used for handbrakes as it has proven very difficult to design a disc brake suitable for holding a car when it is not in use oreover, it is very easy to fit a drum handbrake inside a disc brake so that one unit serves as both service brake and handbrake
6arly type brake shoes contained asbestos When working on brake systems of older cars, care must be taken not to inhale any dust present in the brake
1-
assembly (he nited !tates =ederal *overnment began to regulate asbestos production, and brake manufacturers had to switch to non.asbestos linings 4wners initially complained of poor braking with the replacementsC however, technology eventually advanced to compensate 5 majority of daily.driven older vehicles have been fitted with asbestos.free linings any other countries also limit the use of asbestos in brakes
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8ORKING S$>!1
+n our project we are using scooter front wheel and its braking lever is attached with pnumatic cylinder
we are controlling pnumatic cylinder with anual 5ir 7ontrol Dalve and this controlling valve is transfer compressed air in to the pneumatic cylinder as shown above "We are using air compressor for compressed air#
H= M'#%'9 A+ C#+9 V'92$ =+,/ 1'
S$>!
we are using dc gear motor attached with wheel shaft with help of chain and gear assembly 10
wheel are moving when dc motor turnning chain assambly attached with
S$>!3
We are using cutoff switch for stop dc gear motor while we applied drum brake through pnumatic cylinder
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COMPONENTS RE?UIREMENTS
1 (W4 W366>6A =A4?( W366> ' %?65(+7 7E>6?&6A
1/
0 5?5> 5+A 74?(A4> D5>D6 8 %?65(+7 %+%6 / %?+(+7 74??67(4A @ &7 *65A 4(4A : 7(4== !W+(73 9 )65A+?* B 735+? 5?& *65A 5!!5)>E 1-=44(%5& 11(A5?!=4A6A "=4A &7 4(4A# 1')4&E =A56 MANY MORE AS PER REQUIREMENTS…
PROJECT DESCRIPTION SAFETY SYSTEM<
(he aim is to design and develop a control system based on pneumatic breaking system of an intelligent electronically controlled automotive 1@
braking system )ased on this model, control strategies such as an
'/$ : $ #$= &$+# 2$*9$ /'99 #*9%$ $ •
&evelopment of improved 5)! control systems
1:
•
&evelopment and assessment of an electro.hydraulic.))W "63. ))W# system
•
+ndividual wheel braking combined with traction control
•
5ssessing sensor failure and fault tolerant control system design
•
%reliminary studies into an electrically actuated system
•
Ae.engineering using simplified models PNEUMATICS
(36 W4A& G%?65H 746! =A4 *A662 5?& 65?! )A65(36A W+?& (36 W4A& %?65(+7! +! (36 !(&E 4= 5+A 4D66?( 5?& +(! %36?46?5 +! &6A+D6& =A4 (36 W4A& %?65 (4&5E %?65(+7! +! 5+?>E ?&6A!(44& (4 65?! (36 5%%>+75(+4? 4= 5+A 5! 5 W4A2+?* 6&+ +? +?&!(AE 6!%67+5>>E (36 &A+D+?* 5?& 74?(A4>>+?* 4= 573+?6! 5?& 6I+%6?( %neumatics has for some considerable time between used for carrying out the simplest mechanical tasks in more recent times has played a more important role in the development of pneumatic technology for automation %neumatic systems operate on a supply of compressed air which must be made available in sufficient quantity and at a pressure to suit the capacity of the system When the pneumatic system is being adopted for the first time, however it wills indeed the necessary to deal with the question of compressed air supply (he key part of any facility for supply of compressed air is by means using reciprocating compressor 5 compressor is a machine that takes in air, gas at a certain pressure and delivered the air at a high pressure
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7ompressor capacity is the actual quantity of air compressed and delivered and the volume expressed is that of the air at intake conditions namely at atmosphere pressure and normal ambient temperature THE
COMPRESSIBILITY
OF
THE
AIR
8AS
FIRST
INVESTIGATED BY ROBERT BOYLE IN 1@6 AND THAT FOUND THAT THE PRODUCT OF PRESSURE AND VOLUME OF A PARTICULAR ?UANTITY OF GAS.
(he usual written as %D J 7
"or# %KDK J %'D'
+n this equation the pressure is the absolute pressured which for free is about 18: %si and is of courage capable of maintaining a column of mercury, nearly 0- inches high in an ordinary barometer 5ny gas can be used in pneumatic system but air is the mostly used system now a days
DISK BRAKE
&isc.style brakes development and use began in 6ngland in the 19B-s (he first caliper.type automobile disc brake was patented by =rederick William >anchester in his )irmingham, 2 factory in 1B-' and used successfully on >anchester cars 3owever, the limited choice of metals in this period, meant that he had to use copper as the braking medium acting on the disc (he poor 1B
state of the roads at this time, no more than dusty, rough tracks, meant that the copper wore quickly making the disc brake system non.viable "as recorded in (he >anchester >egacy# +t took another half century for his innovation to be widely adopted odern.style disc brakes first appeared on the low.volume 7rosley 3otshot in 1B8B, although they had to be discontinued in 1B/- due to design problems 7hryslertd with the introduction of a &eluxe version of the Lensen /81 with &unlop disc brakes (he next 5merican production cars to be fitted with disc brakes were the 1B@0 !tudebaker 5vanti "optional on other !tudebaker models#, standard equipment on the 1B@/ Aambler arlin "optional on other 57 models#, and the 1B@/ 7hevrolet 7orvette !tingray "7'# &isc brakes offer better stopping performance than comparable drum brakes, including resistance to N brake fadeN caused by the overheating of brake components, and are able to recover quickly from immersion "wet brakes are less effective# nlike a drum brake, the disc brake has no self.servo effect and the braking force is always proportional to the pressure placed on the braking pedal or lever
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any early implementations for automobiles located the brakes on the inboard side of the driveshaft, near the differential, but most brakes today are located inside the road wheels "5n inboard location reduces the un sprung weight and eliminates a source of heat transfer to the tires, important in =ormula 4ne racing# &isc brakes were most popular on sports cars when they were first introduced, since these vehicles are more demanding about brake performance &iscs have now become the more common form in most passenger vehicles, although many "particularly light weight vehicles# use drum brakes on the rear wheels to keep costs and weight down as well as to simplify the provisions for a parking brake 5s the front brakes perform most of the braking effort, this can be a reasonable compromise
DISCS
5 cross.drilled disc on a modern motorcycle (he design of the disc varies somewhat !ome are simply solid cast iron, but others are hollowed out with fins or vanes joining together the disc
'1
any higher performance brakes have holes drilled through them (his is known as cross.drilling and was originally done in the 1B@-s on racing cars )rake pads will outgas and under use may create boundary layer of gas between the pad and the disc hurting braking performance 7ross.drilling was created to provide the gas someplace to escape 5lthough modern brake pads seldom suffer from outgassing problems, water residue may build up after a vehicle passes through a puddle and impede braking performance =or this reason, and for heat dissipation purposes, cross drilling is still used on some braking components, but is not favored for racing or other hard use as the holes are a source of stress cracks under severe conditions &iscs may also be slotted, where shallow channels are machined into the disc to aid in removing dust and gas !lotting is the preferred method in most racing environments to remove gas, water, and de.gla;e brake pads !ome discs are both drilled and slotted !lotted discs are generally not used on standard vehicles because they quickly wear down brake padsC however, this removal of material is beneficial to race vehicles since it keeps the pads soft and avoids verification of their surfaces
A &%#'# 7,$ /* 7+',$
4n the road, drilled or slotted discs still have a positive effect in wet conditions because the holes or slots prevent a film of water building up
''
between the disc and the pads 7ross drilled discs may eventually crack at the holes due to metal fatigue 7ross.drilled brakes that are manufactured poorly or subjected to high stresses will crack much sooner and more severely ?ew technology now allows smaller brake systems to be fitted to bicycles, mopeds and now even mountain bikes (he market for mountain bike disc brakes is very large and has huge variety, ranging from simple, mechanical "cable# systems, to highly expensive and also powerful, @.pot hydraulic disc systems, commonly used on downhill racing bikes +mproved technology has seen the creation of the first vented discs for use on mountain bikes (he vented discs are similar to that seen on cars and have been introduced to help prevent heat fade on fast alpine descents (he first use of disc brakes on mountain bikes utili;ed mechanical braking systems which did not offer solid braking power, which is why disc brakes were not popular among mountain bikers until hydraulic disc brakes were presented ost mountain bike brake rotors are made from stainless steel and are very thin !ome use a two.piece floating rotor style, and some lightweight rotors are made from aluminum&isc brake discs are commonly manufactured out of a material called grey iron (he !56 maintains a specification for the manufacture of grey iron for various applications =or normal car and light truck applications, the !56 specification is L801 *0--- "superseded to *1-# (his specification dictates the correct range of hardness, chemical composition, tensile strength, and other properties necessary for the intended use
'0
3istorically, brake discs were manufactured throughout the world with a strong concentration in 6urope, and 5merica )etween 1B9B and '--/, manufacturing of brake discs is migrating predominantly to 7hina
RACING
5 reinforced carbon brake disc installed on a =errari =80- 7hallenge race car
8ARPING
Warping is often caused by excessive heat When the disc
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excessively machined brake discs, excessive braking "racing, descending hillsFmountains#, NridingN the brakes, or a NstuckN brake pad "pad contacts the disc at all times# easuring warping is accomplished using a dial indicator on a fixed rigid base, with the tip perpendicular to the brake rotor
'/
tightening as well as a torque rating for the bolts >ug nuts should never be tightened in a circle !ome vehicles are sensitive to the force the bolts apply and tightening should be done with a torque wrench !everal methods can be used to avoid overheating brake discs se of a lower gear when descending steep grades to obtain engine braking will reduce the brake loading 5lso, operating the brakes intermittently . braking to slower speed for a brief time then coasting will allow the brake material to cool between applications Aiding the brakes lightly will generate a great amount of heat with little braking effect and should be avoided 3igh temperature conditions as found in automobile racing can be dealt with by proper pad selection, but at the tradeoff of everyday drivability %ads that can take high heat usually do best when hot and will have reduced braking force when cold 5lso, high heat pads typically have more aggressive compounds and will wear discs down more quickly )rake ducting that forces air directly onto the brake discs, common in motorsports, is highly effective at preventing brake overheating (his is also useful for cars that are driven both in motorsports and on the street, as it has no negative effect on drivability 5 further extension of this method is to install a system which mists the discs with water Laguar has reported great reductions in disc temperatures with such a system Warping will often lead to a thickness variation of the disc +f it has run out, a thin spot will develop by the repetitive contact of the pad against the high spot as the disc turns When the thin section of the disc passes under the pads, the pads move together and the brake pedal will drop slightly When the thicker section of the disc passes between the pads, the pads will move apart and the brake pedal will raise slightlyC this is pedal pulsation (he '@
thickness variation can be felt by the driver when it is approximately -1: mm or greater "on automobile rotors# ?ot all pedal pulsation is due to warped discs )rake pad material operating outside of its designed temperature range can leave a thicker than normal deposit in one area of the disc surface, creating run.out due to a NstickyN or NhotspotN that will grab with every revolution of the disc *rease or other foreign materials can create a slippery spot on the disc, also creating pulsation Aotors can be machined to eliminate thickness variation and lateral runout achining can be done in.situ "on.car# or off.car "bench lathe# )oth methods will eliminate thickness variation achining on.car with proper equipment can also eliminate lateral run out due to hub.face non. perpendicularity
SCARRING
)rake discs being polished after scarring occurred !carring "!$ !coring# can occur if brake pads are not changed promptly when they reach the end of their service life and are considered worn out 4nce enough of the friction material has worn away, the pad
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existing brake pads, will be equally usable with new pads +f the scarring is deeper but not excessive, it can be repaired by machining off a layer of the disc
7racking is limited mostly to drilled discs, which may develop small cracks around edges of holes drilled near the edge of the disc due to the disc
'9
that enough brake disc mass remains to absorb racing temperatures and stresses 5 brake disc is a heat sink , so removing mass increases the heat stress it will have to contend with !mall hairline cracks may appear in any cross drilled metal disc as a normal wear mechanism, but in the severe case the disc will fail catastrophically ?o repair is possible for the cracks, and if cracking becomes severe, the disc rotor must be replaced RUSTING
(he discs are commonly made from cast iron and a certain amount of surface rust is normal (he disc contact area for the brake pads will be kept clean by regular use, but a vehicle that is stored for an extended period can develop significant rust in the contact area that may reduce braking power for a time until the rusted layer is worn off again 4ver time, vented brake rotors may develop severe rust corrosion inside the ventilation slots, compromising the strength of the structure and necessitating replacement
CALIPERS
&isc brake caliper "twin.pot, floating# removed from brake pad for changing pads(he brake caliper is the assembly which houses the brake pads and pistons (he pistons are usually made of aluminum or chrome.plated steel
'B
(here are two types of calipers$ floating or fixed 5 fixed caliper does not move relative to the disc +t uses one or more pairs of opposing pistons to clamp from each side of the disc, and is more complex and expensive than a floating caliper 5 floating caliper "also called a Nsliding caliperN# moves with respect to the disc, along a line parallel to the axis of rotation of the discC a piston on one side of the disc pushes the inner brake pad until it makes contact with the braking surface, then pulls the caliper body with the outer brake pad so pressure is applied to both sides of the disc =loating caliper "single piston# designs are subject to sticking failure, which can occur due to dirt or corrosion entering at least one mounting mechanism and stopping its normal movement (his can cause the pad attached to the caliper to rub on the disc when the brake is not engaged, or cause it to engage at an angle !ticking can occur due to infrequent vehicle use, failure of a seal or rubber protection boot allowing debris entry, dry.out of the grease in the mounting mechanism and subsequent moisture incursion leading to corrosion, or some combination of these factors 7onsequences may include reduced fuel efficiency, excessive wear on the affected pad, and friction.induced heat warping of the disc Darious types of brake calipers are also used on bicycle rim brakes PISTONS AND CYLINDERS
(he most common caliper design uses a single hydraulically actuated piston within a cylinder, although high performance brakes use as many as twelve odern cars use different hydraulic circuits to actuate the brakes on each set of wheels as a safety measure (he hydraulic design also helps multiply braking force (he number of pistons in a caliper is often referred to as the
0-
number of
(he brake pads are designed for high friction with brake pad material embedded in the disc in the process of bedding while wearing evenly 5lthough it is commonly thought that the pad material contacts the metal of the disc to stop the car, the pads work with a very thin layer of their own material and generate a semi.liquid friction boundary that creates the actual braking force 4f course, depending on the properties of the material, disc wear rates may vary (he properties that determine material wear involve trade.offs between performance and longevity (he brake pads must usually be replaced regularly "depending on pad material#, and most are equipped with a method of alerting the driver when this needs to take place !ome have a thin piece of soft metal that rubs against the disc when the pads are too thin, causing the brakes to squeal, while others have a soft metal tab embedded in the pad material that closes an electric circuit and lights a warning light when the brake pad gets thin ore expensive cars may use an electronic sensor
01
5lthough almost all road.going vehicles have only two brake pads per caliper, racing calipers utili;e up to six pads, with varying frictional properties in a staggered pattern for optimum performance 6arly brake pads "and linings# contained asbestos When working on an older car
!ometimes a loud noise or high pitch squeal occurs when the brakes are applied ost brake squeal is produced by vibration "resonance instability# of the brake components, especially the pads and discs "known as forcecoupled excitation# (his type of squeal should not negatively affect brake stopping performance !imple techniques like adding chamfers to linings, greasing or gluing the contact between caliper and the pads "finger to backplate, piston to backplate#, bonding insulators "damping material# to pad backplate, inclusion of a brake shim between the brake pad and back plate, etc may help to reduce squeal 7old weather combined with high early morning humidity "dew# often makes brake.squeal worse, although the squeal stops when the lining reaches regular operating temperatures &ust on the brakes may also cause squealC there are many commercial brake cleaning products that can be used to remove dust and contaminants =inally, some lining wear indicators are also designed to squeal when the lining is due for replacement
0'
4verall brake squeal can be annoying to the vehicle passengers, passers.by, pedestrians, etc especially as vehicle designs become quieter ?oise, vibration, and harshness "?D3# are among the most important priorities for today
)rake judder is usually perceived by the driver as minor to severe vibrations transferred through the chassis during braking (he judder phenomenon can be classified into two distinct subgroups$ #ot "or t#er$al # , or cold Ludder3ot judder is usually produced as a result of longer, more moderate braking from high speed where the vehicle does not come to a complete stop+t commonly occurs when a motorist decelerates from speeds of around 1'- kmFh to about @- kmFh, which results in severe vibrations being transmitted to the driver (hese vibrations are the result of uneven thermal distributions, or #ot "pot" 3ot spots are classified as concentrated thermal regions that alternate between both sides of a disc that distort it in such a way that produces a sinusoidal waviness around its edges 4nce the brake pads "friction materialFbrake lining# comes in contact with the sinusoidal surface during braking, severe vibrations are induced, and can produce ha;ardous conditions for the person driving the vehicle 7old judder, on the other hand, is the result of uneven disc wear patterns or &(D "disc thickness variation# (hese variations in the disc surface are usually the result of extensive vehicle road usage &(D is usually attributed 00
to the following causes$ waviness of rotor surface, misalignment of axis "runout#, elastic deflection, thermal distortion, wear and friction material transfers BRAKE DUST
When braking force is applied, small amounts of material are gradually ground off the brake pads (his material is known as Nbrake dustN and a fair amount of it usually deposits itself on the braking system and the surrounding wheel )rake dust can badly damage the finish of most wheels if not washed off 5irborne brake dust is known to be a health ha;ard, so most repair manuals recommend the use of a chemical
SOLENOID VALVE
08
5 S9$# V'92$ is an $9$*+&$*'#*'99 operated 2'92$ (he valve is controlled by an $9$*+* *%++$# through a /9$#$ in the case of a two. port valve the flow is switched on or offC in the case of a three.port valve, the outflow is switched between the two outlet ports ultiple solenoid valves can be placed together on a &'#:9 !olenoid valves are the most frequently used control elements in :9%*/ (heir tasks are to shut off, release, dose, distribute or mix fluids (hey are found in many application areas !olenoids offer fast and safe switching, high reliability, long service life, good medium compatibility of the materials used, low control power and compact design )esides the plunger.type actuator which is used most frequently, pivoted. armature actuators and rocker actuators are also used (here are many valve design variations 4rdinary valve can have many ports and fluid paths 5 '.way valve, for example, has ' portsC if the valve is *9/$, then the two ports are connected and fluid may flow between the
portsC if the valve is >$#, then ports are isolated +f the valve is open when the solenoid is not energi;ed, then the valve is termed N+&'99 O>$# "?4# !imilarly, if the valve is closed when the solenoid is not energi;ed, then the valve is termed N+&'99 C9/$ (here are also 0.way and more complicated designs 5 0.way valve has 0 portsC it connects one port to either of the two other ports "typically a supply port and an exhaust port#
0/
!olenoid valve are also characteri;ed by how they operate 5 small solenoid can generate a limited force +f that force is sufficient to open and close the valve, then a +$* '*#- solenoid valve is possible 5n approximate relationship between the required solenoid force % ", the fluid pressure P , and the orifice area A for a direct acting solenoid value is$
Where d is the orifice diameter 5 typical solenoid force might be 1/ ? "08 lbf # 5n application might be a low pressure "eg, 1- pounds per square inch "@B k%a## gas with a small orifice diameter "eg, 0 O 9 in "B/ mm# for an orifice area of -11 sq in ":1P1- Q/ m'# and approximate force of 11 lbf "8B ?##
0@
When high pressures and large orifices are encountered, then high forces are required (o generate those forces, an #$+#'99 >9$ solenoid valve design may be possible +n such a design, the line pressure is used to generate the high valve forcesC a small solenoid controls how the line pressure is used +nternally piloted valves are used in dishwashers and irrigation systems where the fluid is water, the pressure might be 9- pounds per square inch "//- k%a# and the orifice diameter might be 0 O 8 in "1B mm# +n some solenoid valves the solenoid acts directly on the main valve 4thers use a small, complete solenoid valve, known as a pilot, to actuate a larger valve While the second type is actually a solenoid valve combined with a pneumatically actuated valve, they are sold and packaged as a single unit referred to as a solenoid valve %iloted valves require much less power to control, but they are noticeably slower %iloted solenoids usually need full power at all times to open and stay open, where a direct acting solenoid may only need full power for a short period of time to open it, and only low power to hold it 5 direct acting solenoid valve typically operates in / to 1- milliseconds (he operation time of a piloted valve depends on its si;eC typical values are 1/ to 1/- milliseconds 8ORKING THEORY OF SOLENOID VALVE
(he main working theory of solenoid valve is that there is a fully closed cabinet inside the valve, with holes in different position 6ach hole is connected with different hose (he valve is centered with two electric magnets aside, when the power is on, the valve will be pulled to that side
0:
(hough the movement of the valve, the hole which is connected to the hose will be closed F open, the oil inlet is always open, the hydraulic oil flows to different hoses and push the cylinder piston by its pressure (he piston drives the piston stem and then the equipment into movement by this means, the mechanical movement can be controlled by controlling the electricity of solenoid valve INTERNALLY PILOTED
While there are multiple design variants, the following is a detailed breakdown of a typical solenoid valve design 5 solenoid valve has two main parts$ the solenoid and the valve (he solenoid converts electrical energy into mechanical energy which, in turn, opens or closes the valve mechanically 5 direct acting valve has only a small flow circuit, shown within section 6 of this diagram "this section is mentioned below as a pilot valve# +n this example, a diaphragm piloted valve multiplies this small pilot flow, by using it to control the flow through a much larger orifice !olenoid valves may use metal seals or rubber seals, and may also have electrical interfaces to allow for easy control 5 />+#- may be used to hold the valve opened "normally open# or closed "normally closed# while the valve is not activated
09
5.+nput side ). &iaphragm 7. %ressure chamber &. %ressure relief passage 6. !olenoid =. 4utput side (he diagram to the right shows the design of a basic valve, controlling the flow of water in this example 5t the top figure is the valve in its closed state (he water under pressure enters at A B is an elastic diaphragm and above it is a weak spring pushing it down (he diaphragm has a pinhole through its center which allows a very small amount of water to flow through it (his water fills the cavity C on the other side of the diaphragm so
0B
that pressure is equal on both sides of the diaphragm, however the compressed spring supplies a net downward force (he spring is weak and is only able to close the inlet because water pressure is equali;ed on both sides of the diaphragm 4nce the diaphragm closes the valve, the pressure on the outlet side of its bottom is reduced, and the greater pressure above holds it even more firmly closed (hus, the spring is irrelevant to holding the valve closed (he above all works because the small drain passage D was blocked by a pin which is the armature of the /9$# E and which is pushed down by a spring +f current is passed through the solenoid, the pin is withdrawn via magnetic force, and the water in chamber & drains out the passage ' faster than the pinhole can refill it (he pressure in chamber C drops and the incoming pressure lifts the diaphragm, thus opening the main valve Water now flows directly from A to F When the solenoid is again deactivated and the passage D is closed again, the spring needs very little force to push the diaphragm down again and the main valve closes +n practice there is often no separate springC the elastomer diaphragm is molded so that it functions as its own spring, preferring to be in the closed shape =rom this explanation it can be seen that this type of valve relies on a differential of pressure between input and output as the pressure at the input must always be greater than the pressure at the output for it to work
8-
!hould the pressure at the output, for any reason, rise above that of the input then the valve would open regardless of the state of the solenoid and pilot valve COMPONENTS
6xample core tubes ?on.magnetic core tubes are used to isolate the fluid from the coil (he core tube encloses the plug nut, the core spring, and the core (he coil slips over the core tubeC a retaining clip engages the depression near the closed end of the core tube and holds the coil on the core tube !olenoid valve designs have many variations and challenges 7ommon components of a solenoid valve$ •
!olenoid subassembly
•
Aetaining clip "aka coil clip#
•
!olenoid coil "with magnetic return path#
•
7ore tube "aka armature tube, plunger tube, solenoid valve tube, sleeve, guide assembly#
•
%lugnut "aka fixed core#
•
!hading coil "aka shading ring#
81
•
7ore spring "aka counter spring#
•
7ore "aka plunger, armature#
•
7ore tubeRbonnet seal
•
)onnet "aka cover#
•
)onnetRdiaphramRbody seal
•
3anger spring
•
)ackup washer
•
&iaphram
•
)leed hole
•
&isk
•
Dalve body
•
!eat
(he core or plunger is the magnetic component that moves when the solenoid is energi;ed (he core is coaxial with the solenoid (he core +'=#- !uch a design simplifies the sealing problems because the fluid cannot escape from the enclosure, but the design also increases the magnetic path resistance because the magnetic path must traverse the thickness of the core tube twice$ once near the plugnut
8'
and once near the core +n some other designs, the core tube is not closed but rather an open tube that slips over one end of the plugnut (o retain the plugnut, the tube might be crimped to the plugnut 5n 4.ring seal between the tube and the plugnut will prevent the fluid from escaping (he solenoid coil consists of many turns of copper wire that surround the core tube and induce the movement of the core (he coil is often encapsulated in epoxy (he coil also has an iron frame that provides a low magnetic path resistance MATERIAL
(he valve body must be compatible with the fluidC common materials are brass, stainless steel, aluminum, and plastic (he seals must be compatible with the fluid (o simplify the sealing issues, the plugnut, core, springs, shading ring, and other components are often exposed to the fluid, so they must be compatible as well (he requirements present some special problems (he core tube needs to be non.magnetic to pass the solenoid
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TYPES
any variations are possible on the basic, one.way, one.solenoid valve described above$ •
one. or two.solenoid valvesC
•
+$* *%++$# or '9$+#'#- *%++$# poweredC
•
different number of ways and positionsC COMMON USES
!olenoid valves are used in :9% >=$+ pneumatic and hydraulic systems, to control cylinders, fluid power motors or larger industrial valves 5utomatic ++-'# />+#,9$+ systems also use solenoid valves with an automatic *#+99$+ &omestic ='/#- &'*#$/ and /='/$+/ use solenoid valves to control water entry into the machine !olenoid valves are used in $#/ *'+/ to control air and water flow +n the >'#7'99 industry, solenoid valves are usually referred to simply as NsolenoidsN (hey are commonly used to control a larger valve used to control the propellant "usually compressed air or 74 '# +n addition to this, these valves are now been used in household water purifiers "A4 systems# )esides controlling the flow of air and fluids, solenoids are used in pharmacology experiments, especially for patch.clamp, which can control the application of agonist or antagonis
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SOLENOID VALVE BASICS
(he illustration below depicts the basic components of a solenoid valve (he valve shown in the picture is a normally.closed, direct.acting valve (his type of solenoid valve has the most simple and easy to understand principle of operation
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(he media controlled by the solenoid valve enters the valve through the inlet port "%art ' in the illustration above# (he media must flow through the orifice "B# before continuing into the outlet port "0# (he orifice is closed and opened by the plunger ":# (he valve pictured above is a normally.closed solenoid valve ?ormally. closed valves use a spring "9# which presses the plunger tip against the opening of the orifice (he sealing material at the tip of the plunger keeps the media from entering the orifice, until the plunger is lifted up by an electromagnetic field created by the coil (he video animation below shows the operation sequence for a direct.acting solenoid valve
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