bqsichydroulicvolves

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iliTfi;rfifiih Tidak untuk diperjuai-belikan atau diperbanyak

tl,lDEX

The following pages contain information about the folLowing hydraulicvalves found in Caterpillar hydraulic systems:

PAGE S{IBJECT PACE SUBJECT

5 Spool Valve

7 Sinple Relief Valve

9 Pilot-Operated Relief Valve

13 Plston-Operated Relief Valve

35 Orifice Check Valve

37 Sinple l{echanicalProtective Device

39 tlechanical ProtectiveDevice with Spool Valve

15 Rest,riction-Type Relief Valve 43 tlydraulic ProtectiveValve Co'mbined r'rithNeutralizer Function

19 Make-Up Valve 47 Hydraulic ProtectiveValve Combined withSeguence Valve

ZL Flow Control Valve 51 Combiaation VaLve

23 Flow Divider Valve 55 Protective Reset Valve

25 Pressure Reduclng Valve 57 NeutraLizer Valve

27 Pressure Diffetential- 59 Hydraulic Shift GovernorValve

5L PrioritY Valve29 l{odifLed Pilot-Operated

Relief Valve 63 Rotary Selector Spool

33 Modulatlng Relief Valve 65 llodulating Reducing Valve(Shown in Valve Station)

** * * * * * * *

INTROBUCTION

The illustrations in this book will help you to recognize the type of valve,its purpose, how it operates, and where it is used.

It is suggested that you use a set of colored pencils to show oil flowthrough the valve diagrams.

Keep this book as a reference; it will help you review the function anduse of hydraulic valves.

Befqre cwrmencing the review of hydraulic valves, consider the followingpoints, vhich will allow you to solve most problems:

t. SPRINGS: - Their purpose in hydraulic ci-rcuits.

A. Before pump commences oil flow, the springs will be fullyexpanded to the lfulit of the housing or compartment r*rerethey are located.

B. They can be ccmpressed or expanded by oil pressure, but willreturn to t.heir original length r^rhen the system is depressurized.

2. VALVES:

- Simply block or control oil flor+.(sornetimes at a predetermined rate)

3. PRESSURE: Comes only r+ith resistance to oil flow,

4. HYDRAT'LIC CIRCUITS:

Read them like a map; the valves are sign posts for oilf ]-ow.

5. TROI'BLESHOOTING:

A. Get a clear pieture of the problem;write down factors concerned if it helps.

B. Try to understand what must be done. A few minutes ofthought can save hours of labor.

C- Like any journey, start at the beginning and follor*through to the source of the problem.

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SPOOL VALVE

I. PURPOSE:B16;f or direct the flow of oil to the desired circuit

2. TY PES:ll-ftoo Positiqn (i.e., !'orward, Reverse)

B. Three Position (i.e., Raise, llold, Lower)

C. Four Position (i.e., Raise, l{old, Lower, ftoat)

3. CONSTRUCTION:A. La"ds that can be moved to select a circuit, (i.e., l, 2 ot 3)

B. Throttling slots machined in lands to allow Partial flow,(i.e., close blade control)

C. Ilachine grooves around the valve land to assist in lubricating,sealing and centering the spool in the bore

4. \",IIIERE USED :

A. - B"ll,tozer hydraulic controls

B. Track loader hydraulic controls

C. Transmission hydraulic controls

D. Implement hydraulic controls

TR(IUBLESHOOTING

NgTii: High pressure applj-cation spool is not available without a matched body.

Low pressure application spooJ- (such as power shift transmi.ssion spool)is many ti$es individually available.

Parts Books, in some instances, list .020tt oversize bore and spool.Re;rson -- to s;rl vilge body machj.ned oversize in utattufacture.

5

I{ALFUNCTION POSSIBLE CAUSE CORRECTION

Blade or bucket drift

Jamming in bore

A. Leakage between spoolland and valve bodY

B. Worn sealsA. Foreign material

jamming spoolB. Valve body improperly

torqued at assemblyC. ]lounting face not flat

Replacement of danagedc omponent sReplaceClean

Refer to speciflcationfor torque andtightening sequence

SIMPLE RELIEF VALVE

\,

+

TANK

BODY

VALVE

OPEN

CLOSED

S EAT

<b PUI,P

6

SIMPLE RELIEF VALVE

I. PURPOSE:T6-T*TI maximum pressure

2, CONSTRUCIION:ffi, sea,t and spring

3. OPEMTION:Va'i-ve is initially held closed by spri.ng force. Pressure oil actsupon the valve. Excessj.ve pressure (always sensed on upstream side ofcircuit) wlll overccne the spri-ng force and open the valve to allow theoil to be bypassed.

4. WHERE USED:d, ---[o]rEessure applieations wtrere exact pressure is not critical

B. ' Booster and lubricatlon systems

C. When noise frm operation is not critical

TftOUBLESHOOTING

}TALFUNCTION POSSIELE CAUSE CORRECTION

Pressure

High pressure

A. Broken or weak spring

B. Faulty seat

C. Foreign matertal jammedunder valve seat

D. Incorrect shi.ms

A. Poppet jammed

B. Incorrect shims

Replaee

Replace or recut

Clean or replace

Adjust

Warped body; dirtin valve

Adj ust

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I

PILOT-OPERATEII RELIEF UALVE

T. PURPOSE;A. To limit maximum pre$sure

B, To protect the hydraulie system from pressure created by excessive' load or blocked line

2. CONS?RUCTTON:m't "alv% two springs and unloading valve with orifice

3. OPEMTION:Oil.nt"rs the relief valve housing and flows through the unloadingvalve orifice to contact the piJ-ot val-ve.

lihen oil pressure rises to the relief valve settj-ng, the pilot valveopers and dumps oi1 from the unloading valve spring charnber.

Since more oil can flow past the pilot valve than through the unloadingvalve orifice, the pressure lesseas in the unloading valve spring chamber.The unloading valve then moves up, allowi-ng full purnp flow to be dumpedinto the taak.

{QIE: Throttling holes in the base of, the unloading valve allow forsmooth dumping.

4. WHERE USED:A. Ali tractor bydrarrlic coo[rol-s

B. All track loarier hydraulic controls

C, AII scraper hydraulic eontrols

5. WIIY USED:A. Less flutter or haurmering

B. Large volume of oil can be passed quickly through a large dumpportn with use of only a smal-l spring and small mechanicalcons t ruct ion,

C. llaintains uniforrn pressure with r,ridely dif ferent flow rates

I

TTOUBLESHOOTING

I{AT,FUNCTTON POSST}LE CAUSIi CORRECTION

Presgure setting high

Pressure settlng 10$

Erratlc operation

AB

Iixcess number of shi:nsIncorrect spring onpilot valvePump flow excessiveInsufficient number ofshimsForeign material jammedunder pilot valve seatLeakage frsn unl"oadingvalve chamberPilot valve seat wornPilot valve springretalner tooseUnloading valve jammedoPenUnloadlng valve sticking

C

A

D

E

llorn ptlot valve

Remove and resetReplace

tlatch valve to pumpAdd and reset

Dlsmantle and clean

Replace O-rings

ReplaceAssenftble correctly

Free valve 1n bore

Check for boredi,s tor t ionCheck for foreignmaterial in oilReplace

10

NOTES

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12

PISTOT{.OPEHATEI} HELIEF VALVE

I. PURPOSE:gl_ l,i*:-t maxi-mum pressure

B. Protect. the lines, cyllnders and vaLve fron pressure createdby an external force on the bucket

2, CONSTRUCTION:ffiGIE", springs and shims

3. OPERATION:OiT tr.pped in the hydraulic lines by the main control. valve can bepressurized by an external force on the track loader bucket cr byblocked bucket linkage, and is isolated fron the main relief valve.

The pressr"lre oil will enter the valve and act on the piston. hthensufficient force is available, the valve will move against the springand dump some oil until overpressure is relieved.

4. WHERT] USED:i6iii-!l3Er "f rlier tilt circuit of botir the wheel and track-type loa<lers.ln some cases, two pistons are used to sense pressures irr diffcrlntcircults" Thc valve is then called "dual sensing.r'

TR0U BLE$H00Tll-lS

I{ALFUNCTlON POSSISLE CAUSE CORRiic'TION

Hose, tllt or liftcylinder failure ordauage due toexeessive pressure

Relief valveinoperative

Buckr:t drift

Relief valve inoperative

A Piston seized inhorrs ingHydraulie lock inspring charnberIlurnp valve scizedl,eakage of O-rlrrgseals, 0r pa$t, valvegeatllei ief valve opcningbclor,'r pr(}s$ur(} scttingof nrain reli-ef valve

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Rernove and repair

lle;r lace

C.lear drlitr pil$silgs

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RESTRICTION-TYPE RELIEF VALVEI. PURPOSE:

ffi-ffially restrict purnp flow, and. establish the system pressure

2. CONSTRUCTION:Valve with an orifice and chanber open to pump pressure flow and spring.Some have a piston (slug) in orifice chamber.

3. OPEMTION:ffive cr"ates restriction to purnp flow by blocking the outlet.

As the system fllls, pressure rises through the orifice into theehamber and moves the valve against the spring until tEe outlet isopened.

0i1 ean then flow past the valve to limit pressure rise.

A pistou (or slug) used in the orifice chamber will allow a lightspring to control the actlon of the valve because the pressure oilwill be acting on a reduced area.

A poppet may be used to dampen the action of the valve by slowing itsclosing rate.

4, \JHER.E USED:Transmission hydraulic controls for some traek-type tractor$, track-type loaders, small and large wheel loaders

TROUBLE$HOOTING

I,lALFUNCTION POSSIiLE CAUS}J CORRHCTION

Low pressure

tligtr pressure

Erratic cond{tion

Insufflclent number ofshimsSoft shins used andbcaten outIncorrect or brokens pringSlug (if used) nissingI)r;rj-n p:rssages betrintlslug blockedExcess number of shi.msPressure not enteringorificeValve scizcd in boreSlug ( if used) seizedin valveIncsrrect sprlng

RelieI valve larrdworn frtm iiue abraslvesin oilInterrnittent st ic.l<irrg

D

E

AB

LD

Add and reset

l{eplace wi th correcthardened shlnsReplace

l{ep I aceReruove olrstruction

ilemove and resetClear blockcdorificclteplace iI tlarnagedClean or rtlpl;rce

Dra in ;rntl f 1 trshsys t cm

Deterrnine sourceof abrasivesReplace vorn partsHree valve irr bore

15

CHECK VALVE

TAPERED SEAT

16

CHECK VALVE

1. PURPOSE:To control oil to flow in one direct.ion only

2. CONSTR.UCTION:Sprfng a"a;lve with a tapered seat; a round ball is sometimesused instead of the valve shown here. In other ci-rcuits, the checkvalve is free floating (has no sprJ-ngs) or has an orifice in thevalve.

3. OPEMTION:The valve will lift off the seat and control the flow vrhen the slightspring force is exceeded.

4 . W}TERE USED:In dozer, ripper, tilt cylinder and track loader bucket circuits toseParate two circui-ts. In steering clutch clrcuits to prevent pressureloss during transmisslon range selection on power strift machines.

THOU BLE$HOOTII'IG

I{ALT'UNCTION POSSISLE CAUSE CORRECTIOI'I

Bucket or dozer dropsslightLy when ririsepositions seleeted

A. Worrr seat

B, Worn valve

C. Broken spring

D. Dirt under valve

Recrrt or replace

Replaee

Replace

Clean

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18

MAKE.UP VALVE

I. PURPOSE;ilf6"iloil ro bypass tire pump and flow directly to tle cylinderlines whenever reservoir pressure is greater than line pressure

2. CONSTRUCTION:m-egffiT;a-and light spring. Valve will ah+ays be located belowreservoir oil level. There will be one for each circuit-

3. OPERATION:ffi; oil pressure in lines is approximately 2 psi less than reservoirpressure, the make-up valve unseats, allowing oil to flow to lines.(Example: quick dropping blade or bucket.) This prevents cavitationin cylinders and lines.

4 . r{ilERts US ED:

Do#; ripper aud track loader hydraulic circuits

TROUBLESHOOTING

I1ALI.'TJNCTION POSSIBLE CAUSE COITR[C'I'ION

Itlade or bucket drift

Blade will" not lift

Blade lacks downpr essu re

A. Valve jammed opcn

B. Valve jarurned open

C. V:rlve jammed open

Clean or replirce

Clean or replace

0k:"irrr or rep.Lacc

1g

FLOW CONTROL UALUE

20

FLOW CONTROL VALVE

T. PURPOSE:tloffiiae a predeterurined maximum flow rate to one circuit andbypass excess flow to another circuit

2. CON$TRUCTION:An oriEic" designed to pass a certain flow at a specified. pressuredifferenti,al, and a valve to bypass or restrict excess oil. Thevalve is loaded by a light spring and sometimes the orifice iscontained in the valve.

3. OPERATION:TE'[Tif?fce, beeause of its size, creates a pressure drop across itin.the direction of fl-ow. The force from tire higher pressure actson the upstream side of the valve. The force frorn tire lower pressureplus the spring force act on the downstream side of the valve. Whenthe force differential between the t\,/o pressures rises above thedesired level (r+hen fl:r+ rises above de*ignecl amount), the valve willthen move towards the low pressure side, overeoming spring force.

This action will either bypass cxcess oil ar restrict ttre flow of oilto the valve (dependlrrg on the constructton of the valve). Tl-re flowthrough thc orif ice will rhen be rnirintaincd ;lt a retluired value.

4. \,iIi{ERE USEJ]:'tlran"*i"'sion hydraulic controls, implement hydraulic controls

TROUBLESHOt}TING

}IAL!'UNCTION POSSIBLU CAUSE COITITIiCTION

I)oes not Limit flow

Flow rate too low

Valve seized irr body

l\

Full flow plugi"ns tal l ecl

Valve sprirrg brokerror weak

Val.ve scized, p;rr:ti;rl Lyclosed

Orifiec plug inst;rllcd

Clean or replaceincorrect spring

Replace withorifice plu;i

lleplace 6prlng

Cle:rn or replace

Rcpl;rce with higherflow rate plug

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22

FLOW OIVIOER VALVE

I. PURPOSE:To .q"aily divide the oil flow frorn a single PumP, regardless ofthe difference in restrj-ction on the outlets, alLowing two separatecircuits to be supplied sj-multaneously witir oil from a single pump

2. CONSTRUCTION;Sprol-A;ill.d tc-r atlmit o11 to center, then cross-dritled' to directoil to each separate outLet

3. OPERAIION:'!{TTI'Toi[ outlets providing gqual restriction to the oil leavi.ngthe outiet passaBes 1n the body, the flow dj-vider spool will be

balanced in the center of the body"

I'Jhen the operator restricts oae outlet by applying one brake orsteering clutch and upsetting the balanced flow, a pressure risewill cause the spool to move to tire low pressure side.

The spool itself r*ill then restrict the oil flow from the pump andcause a pressure rise equal to the restrj-ction caused by the actionof the brake or steering clutch.

The oil flow fron the two outlets will then be equal.

4. lil{uitE IJSED:garty -oA;i track loader steering clutcli circuits and track-typetraetor brake booster circuits

TNOUELESHOOTIHG

IlAL}'UNCTION POSSIBLE CAUSE CORRECTIOT.I

Lotu oil pressure whenone brake is applied,correc t rril pressuret+hen both br:akes areapplied

Pressure oil isava ilatr le to onr bra ltt:boost er

Srake pressure is lor.r

A. Valve seized in centralposition

A. Va lvc r;e iz.ed irt ouecrrrd uf tlody

A. lr{ain roliel vslve sel:l.ow

B. Brake reli-ef valvc set!uw

Clean or replace

Clean or rttpl;rct:

Itenove arrd ::ese t

Repl.rcu :;pr itrg

23

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24

PRESSURE BEDUCING VALVE

I. PURPOSE:6*ie-dice pump pressure (established by the nain relief valve), to therequirements of the system

2. CONSTRUCTION:ffildth;lug cfflpartment orifice open to downstream pressure'The sprlng determines dovmstream system pressure.

3. OPEMTION:ITEiiGtty, the valve is held open to flow by the spring.

B. Pressure must build up in the gownstream side and in theslug ehamber.

C.'lJhen pressure builds up sufficient force in chamber, the valvemoves against the spring, reducing the pump flow and maintainingthe reduced pressure.

4. \{HERE USED:ffiiEsi"n hydraulic controls - D6C, 600 Series, 769, 824 and 834.

TROUBLESHOOTING

ITALFUNCTION POSSIBLE CAUSE CORRECTIOI.I

Reduced pressure not tospeciflcation

Pressure not reducedby valve

No pressure sensedon dowrtstfeaur sideof valve

A. Incorrect shimming

B. Inlet pressure low

Spring failedSlug ornitted duringassembly

Orifice blocked

Valve jammed open

Slug seized in valve

Valve jammed closed

Slug seized in valveholding valvt: closed

Oil drain passage bettindslug blocked

Orif ice open to irutnP

Irre$sure f1ow, lroldlrrgvalve closed

L

D

A.

B.

C.

A.

B.

t, -

D.

Add or remove shiins

Determi-ne if lowpressure is due tomain relief valvesetting or lack ofrestriction ondorrnstream side ofpre$sure reducingvalveReplace spring

Replace slug

Clear blockage

F'ree valve in bore

Clcan or replaee

Free valve itr bore

Clean or replaec

Iletc rmine re;r son f ortrydraulic lock

De te rrnine re& son ,posslbly caused bypressure surgc fromdown.s t reanr pusirlrrgvalve orifice intopump flow chamber

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PRESSURE t}IFFEHENTIAL VALVE

PURPOSE:T6'suppry oil at a consrant pressure differential to two circuitsCONSTRUCTION:Valve with passages leading to spring compartrTrent and to the second circui-t

3. OPEMTION:The-a;TEerential val-ve initlally blocks oil flow until pressure rises. ThisPressure rise moves the valve against the spring and allows oil flow into thesecondary circuit.As the pressure rises in tlre secondary cj-rcuit, oil will flow into the spripgcomPartment aad this will" be at the same pressure,as the oil in the secondarycircuit.The pressure of the oil in the spri-ng compartment cornbines with the action ofthe spring to move the valve back agalnst the presPure of the oil in the primarycircuit.The valve rorill tlren f ind a position wirere the pressure in the pri:lary circuitequals the comtrined effect of the pressure in the secondary circuit and thespring force. Regardless of inlet pressure, the difference in pressure bet,n/eenthe primary and secondary circuits is always equal to the equivalent pressureof the spring and is called the "pressure tlifferential". It can only be alteredby changing the spring rate. This can be <lone by changing the spring itself.IJtr1EI{E US ED:Sme power shift transmissi-on control circui"ts; 600 lJlreel Tractor torquedivider transririssions

irlltY USIiD:5.a. Power shift transnissions

engagelnenfb. 600 Series transillissions;

- to ensure correct scqulrnce of cl utclr

part of the autotnatic shif t circrr itTRt)UBLESHOOTING

I1ALFUNCTION POSS TIlLE CAUSE CORi{ECTION

Pressure differentialless t.han specified

Pressure dillerentialgreatcr than speeified

Pressure not droppingin secon,lary circirit ontransrnission whcn shiftis rnadc

Incorrect clr brokenspr ing

0iI leakrng from springchamber

Irrsuf ficient restri{:t i ilnon second circuitfncorrcct spring

V;rlvc jarmmed open

Differential valvenot opening dump port

Replace spring

Determi-ne cause oflcakage

Blimiu;rte Le akage

Replace wiLll corrcct(r,reaker) springReplace courponent ifd;rm;rgedHnsure valve freein bore

27

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MODIFIEO PILOT.OPERATED RELIEF VALVE

t. PURPOSET

e. .Get

maxj-mum system pressure for nonnal operating conditions

B. Relieve pressure surges at a lower value

2, CONSTRUCTION:Ltad pGt"n, load piston orifice, load piston chamber, two springs,pilot valve and unloading valve with orifice

3. OPEMTION:

Oil enters the relief valve housing and flows through the unloadingvalve orifice to the face of the pilot valve and through a passageand orifice to the load piston.

As pressure rises and is sensed in the load piston chamber, the loadpiston moves to the right, eompressing pilot valve spring; thisincreases the pilot valve pressure setting.

The load piston moves before the pilot valve because the area of theload piston is larger than the face of the pilot valve.

When the load piston is hard against the stop, the pilot valve settingis at the normal operating value.

The reroainder of the operation is identical to the operation of thepilot-operated relief valve.

B. Pressure Surgesffie1iefvalvehousingan<lflowsthroughtheun1oarl1ngvalve orifice to the face of the pi-lot valve and to the ori"fice ofthe load piston chamber.

Because of the size of the orifice ln the load piston chamber, flowls restricted, creatlng a delay in pressure to the load plston andresulting in a build-up of pressure along the passage to the faee ofthe pilot valve.

Consequently, when a pressure surge exlsts, the pilot valve will alwaysopen first.

The pilot valve opens and dumps oll frt-rn the unloading valve sprlng charnlrer.

The remainder of the operatlon 1s ldentical to the operation of the pilot-operated rellef valve.

4, WHERE USED:il?ITEie"; scraper portion of hydraultcs

B. 9BB main pressure rellef valve (loader portion)

29

TROUBLE$HOOTING

ITALFUI{CTTON POSSIB I-U CAUSE CORRTCTION

Itressrrre seIting low

Pressure setting high

Erratic operation

A.

B.

lllockcd lcad pistonch;rmber or lf i.ce

Fcreign rnaterial j,ammed

under pilot valvc seat

Leukage ftrm unloadingvalve chambur

f ilot valve seat worrr

Unloadlng valve jammedopen

Pllot valve spring broken

Incorrect spring on Pilotvalve

Punp flow excessive

Unloadlng valvesticki.ng

!.loru pilot valve

D

E

!'

A

A

Itismantle and clean

Dlsmantle and ctean

Replace 0-ring

Replace

Free valve ln bore

lleplace

Replace

llatch valve topLmp

Check for boredlstortion; checkfor forelgn naterlalin oil

Replace

30

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32

MOIIULATING RELIEF VALVE

l. tuRPosE:fo get a variable system pressure and, depending on the application,a delayed pressure buildup

2. CONSTRUCTION:BasiEa Tt a relief valve htith a load piston behind the spring

3. OPEMTION:As in the case of the nornal relief valve, it creates restriction topump flow by closing the outlet. If there is no pressure acting on theload plston it relieves at a low pressure (usually called primary pressure).When the load piston is charged with oil, the relief pressure inereases.The maximum pressure is reached when the load piston is against the stop.

If used in conjunction with an orifice check valve, the pressure buildupwill be slo',r, yet the pressure drop will be rapid''

4. WHERE USED:ffiE'ift transmission hydraulic controls

TROU B LESH O()TING

NOTE:

l'or further troubleshooti.ng, see "Restriction-Type Relief Valve" (page 15).

IlALFUNCTION POSSIBLE CAUSE

Pressure remains at initial setting

No modulation

Slow pressure buildup and slow,instead of rapid relief

A. Load piston sticking or seized

ts. No pressure buildup beyond theload piston

A. Load piston sticking or seized

A. Load piston binding

B. Orifice check valve binding

33

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ORIFICE CHECK VALVE

1. PURPOSE:6-li6-niae a different rate of flow to and from a load piston

2. CONSTRUCTION:ChE;relv.-"ithout spri-ng but with an orifiee

3. OPERATION:0ffro" the supply side moves the valve over and clgses the drain port.Only a metered amount can pass through the orifice.When the flow reverses, the valve i-s moved to the left and uncoversthe draj-n port.The discharge through the drain will be rapid.

4. WHERE USED:Frdeffi'Ift transmj.ssion hydraulic eontrols

TROUBLESHOOTING

I.IOIE: See also modulating relief valve (page 33).

ITALFUNCTION POSSIBLE CAI.'SE

No pressure buildup

Slow pressure relief

A. Check valve stuck, leavingdrain open

B. Orifice blocked

A. Check valve stuck withthe drain closed

35

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36

$ITUPLE MECHANICAL PROTECTIVE DEVICE

I. PURPOSE:ldffi;er pressure in a system drops below a minimum value for a lengthof time, the selector is moved to a safe or neutral posi-tion.

2. CONSTRUCTION:Station"ry piston with a spring-ioaded cyllnder

3. OPERATION:Ttle oj-lrthat cornes in through the rod fills the space between thepiston and the cylinder. As it compresses the spring, it allowsfree movement of the selector spool valve. Ilhen the oil pressureis lost or the engine is stopped, the spring moves the seleetorlever to neutral. A check valve in the piston allovs quick chargingduring pressure increases, but the oil in the cylinder can onl"y leak outat a controlled rate when the sensing pressure decreases. Therefore,the control does not act upon a short pressure drop (as could happen,for instance, r*hen a gear is changed).

4. I'IH8RE USED :

P"wer shift transmissions of scme early machines

TR0U BLESH00TII'lG

IIALFUNCTION POSSIBLE CAUSE

Selector leverany gear

cannot be moved into

Se]ec tor lever isneutral r^rhen the

Ilot returned toenglne is stoppcd

Selector lever jumps to lowergear on deeelerating the engine

A. Linkage obstructed mechanically

B. Transmission pump defect

C. Spring broken in modulatingrelief valve

D

E

Piston and cylinder seized

Passage for oil supply toprotective device blocked

Leaking protectice device

A. Tlght Iinkrge or spool valve

B, Piston arrd cylinder r:fprotective devicc seized

C. Spring broken

A. Transmission pump has lowoutput

B. Suction screen blockedC. Aeration irt suction line

37

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MECHANICAL PROTECTIUE DEUICE WITH SPOOL VALVE

1. PURPOSE:ffiT6'e oil pressure is low in the system, it prevents oil flow tothe dlrect.ional clutches.

2. COI.ISTRUCTION:ATCpG tnechanical protective device with spool valve

3. OPERATION

i,ihen there is no oil pressure, the piston is extended, making itinpossible for the speed selector to be placed in any gear whichalso means tlrat the passage (A) to (B) will be closed.

llhen the devi-ce is charged, it cnmpresses the spring whieh now getsshorter, so that a speed may be selected if desired.

Should the engi-ne be stopped with the selector lever in any gear'or the oll pressure be lost for any reason, the device pushes tirespool valve to the left to Neutral position, which interrupts thepassage (A) to (B).

A check valve in the piston allows quick charging during pressurelncreases, but the oil in the cylinder can only leak out at acontrolled rate when the sensing pressure is lower. Therefore, thecontrol does not act upon a short pressure drop (as eould happen, forinstance, when a gear is changed).

4. I'IHERE USED :

Polrd-shift transmissions of some early rnachines

39

TROUBLESHOOTING

ITALFUNCTION POSSIBLE CAUSE

Selector lever cannot be moved intoany gear

Selector ls not returned toNeutral when the engine isstopped

Sel-ector lever juurps to lowergear on decelerating the engine

A. Linkage obstructed mechanically

B. Transmission pump defect

C. Spring broken in modulatlngreli-ef valve

D. Plstorr arrcl eyllnder seized

E. Passage for oll supply toprotective device blocked

F. Leaki"ng protective device

A. Tight linkage or spool valve

B. Piston and cylinder of protectivedevice seized

C. Spring broken

A. Transmission pump has low output

B. Suction screen blocked

C. Aeration i-n suction line

40

NOTES

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5.

HYORAULIC PNOTECTIVE VALUE

OOMBINEO WITH NEUTRALIZER FUNCTII)N

PURPOS[:A. To prevent the rnachine from rnoving when the engine is started vith the

selector lever in a gear positionB. To neutralize the transmission when tire left brake pedal is depressed,

in conjunction with the neutralizer valve

CONSTRUCTIOI{:Spo6T ;ive*with various lands; in reset position, held by a springto close the passage to the directional clut.ches

OPERATIOII:A. 't^Jh"" the machine is started r*ith the selector lever not in lleutral ,

oil witl not be able t.o get from passage (A) to (B) which eventuallyleads to the directional clut.ches.

Placing the selector lever in Neutral provides pressure frotn passage(C) which can reach cavity (E) through the orifice (l). In reaction'the valve 1s puehed to the left, opening the passage (A) to (B). Ifnow the selector lever i-s moved to }.'orward or Reverse, the increasirrgpressure at (A) can open the valve completely and we have pressure at(B) and pressure in a directionaL clutch.

There is a connection from the neutralizer valve to passage (D). Innornal operation, the valve closes tl'ris passage, but if the Leftbrake pedal is applied, (D) is connected to drain' Because more oilcan drain out than gets int{) cavity (E) , the valve rnoves to the ::iglrtseparating passages (A) and (B) but not so far that the orifices (2)are covered by the land, This interrupts the po\rer flora tltrough tiretransrnission. l.lhen the neutraLieer valve i.s released ' passage (D)

will t:e blockeii and the oil that enters the hole's (2) shifts tlrevalve open again.

WIIERE USED:ffie?=Ei?t transrnission hydraulic controls; for instance, 980

0n scraper transrnissions, s similar type of valve is used, butwithout the neutraLtzer function.

B.

4.

ReviseiJ 218443

TROUBLESHOOTING

IIALFUNCTION POSSIBLE CAUSE

llachine rnoves whenwith the seleetorposition

the engine is startedlever in a gear

Ilachine does notselector is movedReverse

move when theto Forward or

A. Direction clutch, binding

B. Spool valve rnisadjusted

C. Combination valve stickingthat holes (2) communicat,ewith (A)

D. Spring of protective valvebroken

A. Linkage probleru

B. Wrong spool valve adjustment

C. Leak in the directional clutchor in the llne to it

D. Protective valve sticking

E. Neutralizer valve sticking

l'. llodulating relief valve springbroken

C. llodulating relief valve stuckopen

I

J

Load piston of modulat.ingrelief valve stuck in thereset positionTransmission pump failure

Torque converter failure

44

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46

1.from moving wiren the engine is started rsithgear

lirrough the transmission when oil pressure

)

J.

HYDRAULIC PROTECTIVE VALVE

COMBINED WITH SE(IUENCE VALVE

PURPOSE:A. To prevent the machine

the selector lever in a

B. To interrupt power flowis lost

CONSTRUC?1OII:TroE;ing-loaded spool valves. In reset posit.ion, the sequence valvecloses the passage to the pressure control group and clutches.

OPER!{TION:E. tlhen the engine is stqrte , the reset.

ure to enter at TA),

The protective valve rernains at reset position and the oil coming inat {B) goes to drain at the protective valve. There is not enoughforce createcl in the slug cav j.ty ( 1) to inove the sequence valve tothe 1eft.

lJhen the selector lever is moved to lieutral, the reset valve, which isi-zed oil to enter parisage

(A), This moves the protective valve to tlie left and closes the drainport.

Tiie oil entering passage (ll) builds up pressure and the reactitrn in si"ugcavity ( 1) moves the sequence v;rlve to tlie lef t.

The oil now has tire prissage open and oil can f lor+ from {B) to (C).

If the enginr: is stopped or if the oil pressure drops below a safelevel, tire protective valve spring iorces tire valve spool over totire right, relievlng tire pressure in tire slug cavity (l) to drain.The seqirence valve is then forced to tlle right by its spring andseparates the passaCe (B) to (C).

lihen the engine is stiirted or tire l)ressurc reBititred, the selectorIever must be moved to l{eutral position first in order te resetthe protective v;:lve and open tire passaSe {B) to (C) by tite sequencevalve.

$ltERH Utiiio:Power -irilt transntlss j-r:n trycl rar;llc corlf,rol:j ( for instartce, 9uS, t)92,8?_4, Bl4)

4.

47

TROUBLESHOOTING

PROBA.BLE CAUSEIIALFUNCTION

A. ilirectional clutch binding

B. Reset valve mlsadjusted

C. Protective valve seized at the Leftpositiorr

D. Protective valve sPring broken

E. Sequence valve stuek oPen

F. Sequence valve sPring broken

A. Reset valve misadjusted

B. Spool valves misadjusted

C. Leak in the directional clutchor line to it

D. Clutch fai-lure

E. Protective valve sticking in resetposition

F. Sequence valve sticking in resetposit.ion

C. Passage to slug cavity (l) blocked

H. llodulating relief valve springbroken

I. l{odulating relief valve stuck open

J. Load piston of modulating reliefvalve stuck in reset Position

K. NeutraLizer val-ve stuck in'applied position

L. Transrnission PumP failure

11. Torque converter failure

ilachine movesstarted within gear

when the englne isthe selector lever

Itaehine does not move \.rhen theselector lever is moved to Forwardor Reverse fr<rm Neutral

48

NOTES

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1.

COMBINATION VALVE

PURPOSE:al-Eotective valveB. Differential valveC. Flow control valveD. Check valveCONSTRUCTIOI'I:Vafi;;ith *etering orifices loaded by two springs of which onlyone is in contact in reset position. Passagas to or from themodulating relief valve, the directional spool valve, the loadpiston of the directional spool valve, directional clutches and

drains.OPflRATION:A. Prtt.ctive Valve

ffiiSStartedwiththetransmissionseIectorlever

to the selector lever position, willerter passage (B) where it can pass through the holes (2).

I{aving equal pressure on both sides of the spool' the springwill keep it in the reset position and passage (C) cannot receiveoil. The machine cantt move.

llovj-ns, the selector lever to Neutral connects passage (B) to drainthe selector valve gio"p. Oil entering Passage (A) now moves thevalve until 1t relieves into passage (B). The load piston of themodulating relief valve is connected to drain via (C) or (F) dependingupon the application. This establishes the primary pressure inNeutral.

B. Differential Valveffier is taken out of the Neutral position'passage (B) is again connected to pump flow and system pressure.This same pressure enters passage (A). llora the valve can move

tu the right to sequence the clutch engagement. The differencebetween tire speed and directional clutch pressures is controlledby the eombined force of the two springs.

C. Flow Control Valveffiirto pass through into

ices (l) allows only a speeific arnount of oilthe directional clutches during filling'

2.

3.

D. Check ValveP"ss"ge CTThis allowsrelief valve

is blocked when the valve works, as explainedpressure buildup behind the load piston of tile

In Neutral position of the spool valve, and tlhen gears arepassage (3) is connected to drain (C) or (F) (depending on

application) which quickly lowers the system pressure.L.iI{EITE USED:

So-" p"r"t sirift transmission controls (for instance'966C, 950, D4D, 94L, 9518)

under B.modulating

changed,the

L2 14 llotor Graders,4.

llo oil can pass through orlfj-ees (1) in the Neutral position.NOTE:

51

TROUBLESHOOTING

I{ALFIJNCIION POSSIBLE CAUSE

l{achine moveswith selector

when engine is startedlever in a gear position

Machlne does noE moveis moved lo fonrard orNeutral to a speed

when the selectorrevelse or from

Rough shifting

A

B

C

D

Li,nkage problem

Wrong spool valve adjustment

Directional clutch binding

Combination valve stuck in aposition so that holes (2) areopen to passage (C)

Linkage problem

Wrong spool valve adjustrnent

Leak in the directional cLutchor the passage to it

Cornbination valve stuck inreset position

Itodulating relief valve springbroken

llodulating relief valve stuckopen

Load piston of modulatingrelief valve stuck in resetposition

Transmission pump failure

Binding cluteh plates

Combination valve sticking

A

B

C

D

E

_r

G

H

A

B

52

NOTES

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PROTEGTIVE RESET VALVE1. PURPOSE:

G-pr"".nt the machine from moving when the engine is started withthe selector lever in a gear

2. CONSTRUCTION:Normal spo"1 valvel meehanically connected to the speed control spoolvalve

3. OPERATION:

ffiETeutral positJ-on can pump oil enter the passage to the protectivevalve spool to reset it.

4. \FItl[RE US ED:Po"d;hlTt transmission hydraulic controls (for instance, 988, gg2, g|q,834)

TROUBLESHOOTIHG

NOTE:

!'or further troubleshooting hintsi see Protective Valve combined r^ritirSequence Valve (page 47).

MALFUNCTION PROBASLE CAUSE

llachine moves when the engine isstarted with the selector in agear position

llachine does not move when theselector lever is moved toForward or Reverse out of Neutral

A. Protectlve reset valvemisadj ust ed

A. Protective reset valvemisadj us ted

L.

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56

IIIEUTRAIIZEil VALVE

I. PURPOSE:ffiI*otf the oil flor.i to the directional clutches in a power shifttransmission when the left brake pedal is depressed

2. CONSTRUCTION:Cpoof A1'v-e is held by spri-ag force in such a position that the oilgolng to the clutches has a direct passage through to the directionalclutches.

. 3. OPEMTIoN;G-G reset position, the oil can pass straight thro$gh to the directionalclutches. When the left brake is appl-ied, oi!- or air pressure shifts thevalve over and, in so doing, blocks the passage to the directional clutchesand opens the cluteh to drain. This will interrupt the power flow throughthe transnission.

4. WHSRE USED:Por{d;fri3t transmissions of wtreel loaders

TRBUBLESHOOTIHG

MALFUNCTION POSSISLE CAUSE

Transmission does not neutralize

Transmission does not transmitPower

Leak i-n oj-l or air line ofbrake systectr

Neutralizer valve sticking

Mechanical fallure iatransmission

Torque eonverter fallure

llodulating relief valvesticking

Neutralizer valve stickingapplied posit,ion

Broken neutralizer valvespring

B

A

B.

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HYBRAULIC SHIFT GOVERNOR

I. PURPOSE:Iffiaing upon transmj-ssion output shaft rpm, variable pressures arecreated -- working against the reference pressures.

2. COI{STRUCTION:R"t"ti"gT;sing with 3 reducing val-ve spools of different weights.Two of the valve spools contain slugs which are different in size.

3. OPERATION:Basicalit, each of the 3 reducing valve spools represents a normalreducing valve. Since the whole governor rotates, the reducing valvespools are subject to centrlfugal force" The centrifugal force replacesthe spring action in a normal reducing valve because it is trying toopen the incoming pressure to the outlet side.

The outlet pressure, as in a normal reducing valve, is acting to closeoff the inlet. yhen it has reached a certai_n value.

Due to the design of the reducing valve spools, there are various outletPressures produced at. any given speed, The pressures are not adjustable.These pressures work against a fixed reference pressure in the selectorvalve spool group (not shown).

4. WHERE USED:uya;;m;controls of semiautomatic scraper transmissions

TR()UBLESHOOTING

I{ALFUNCTION POSSIBLE CAUSE

Transmission does not automaticallyshift up at all or stops shifting upat 4th or 6th speed

Transmission selects 4th, 5th or Bthspeed as soon as the shift lever isplaced lnto the second gear

A. One of the three reducing valvespools is stuck, closing off theincoming pressure

A. One of the 3 reducing valvespools is stuck in a positionso that the incorni"ng pressuregoes directly to the outletside

59

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60

PRIORITY VALVE

I. PURPOSE;To mak. sure that o!1 ls supplied to a particular circuit before it ispennitted to flor^T to a second circuit

2. CONSTRUCTION:Th" *"st b""ic priority valve group has one inlet and two outlet.passages. There are several varlalions of this design, but the resultsof valve operation are the same for all types.

3. 0.P9MTrON:Supply oil enters the inlet passage and flows to the prJmary circuit.At the same time, the oil opens the poppet valve and fills the slugchamber. lJhen the pressure of the oil in the prlrnary circuit and inthe slug chamber increases to a specific value, the spool moves againstthe spring force and permits oil to flow to the secondary circuit. Apressure desrease (during a shift for example) will cause the valve toclose and block flow to the secondary circuit,

4. WHERE USED:Tra"smis.sion hydraulic controls -- L Series Tractors, 8-speedsemiautomatic transmissions, and 7-speed automatic transmisslons

5. WHY USED:alEeries Tractor transmissions -- to make sure that oil is available

for operation of the steering clutches and brakes before anytransmission clutches are engaged

B, B-speed semiautomatic and 7*speed automatic transmissions -- tomake sure that oil is ;:vailable for operation of the automaticeomponents (autornatic pressure control group, hydraulic governor,and automatic sel-ector group) before any transmission clutchesare engaged

TROUB LESHOOTING

]IALFUNCTION POSSIILE Ci\USE CORI{.ECTION

Trarrsmission c-Lutchesdo not engage

Transmission clutchesslip during eilgageulent

Brakes releaseslowly or not atall (L Series)

A. Valve stuck closed

1l , Opening pressure lr->o

il J-8il

A, Valve stuck opcn

B'. Openirrg pressure toolow

A. l{estriction or blockagein primary circuit

Free valve in bore

Adjust pressuresetting (remove shims)ur replace s1:rlrrgl'rue v;r'l ve in l:ore

At-l;ust pressurest: [, t ing (.rdd shirns)or repLace spring

Detennine cause ofrestricti()rl ()rblockage and remove

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62

ROTARY SELEGTOR SPOOL

I . PI]RPOSE:Direct" the flow of pilot oil to inltiate clutch engagement; providesdrain ports to initj-ate clutch decay and prevent clut.ch engagement

2. CONSTRUCTION:ffi rotary selector spool j-s basically a rotating shaft. lrith a hollowcenter. A plug and screen assembly divides the cent.er cavity into twoseparate charnbers. A detent cam is lnstalled in one end of the spool.

3. OPEMTIOI'I:The ce"ter chamber which houses the screen is normally filled withpilot oil. The chamber which does not contain the screen is alwaysopen to drain. i'lhen the spool is rotated to a gear position, pilotoi1 from the outlet ports is directed to a pressure control valve groupto inj-t.iate engagement of the appropriate clutches.. At the same tirne,the drain ports cause the clutches which uere engaged in the precedinggear range to decay. The detent cam helps to locate each gear positionof the spool.

4 . I.]HERE US ED;ffi-peed semiaut.ornatic transmissions with individial clutchmodulation (ICl{)

TROUBLESHOOTING

I1ALFUNCTlON POSSIBLE CAUSE CORRECTION

Transmission reroainsin a particular gear

Transmisslon clutchesdo not engage

llore than two clutchestry to engage

A. Spool stuck in oneposition

Screen in pilotchamber plugged

Pilot chamber outletports plugged

One or more drainports plugged

Free valve in bore

Disassemble valve groupand clean screen

Disassemble valve groupand clean ports

Disassemble valve groupand clean ports

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l-

MODULATINO REDUCING VALVE

(sH0wN rN vALvE sTATl0N)

PURPOSE:

ffitrofs the pressure rise, maximum pressure, and rate of decay fora specific transmission clutch

CONSTRUCTION:The;A;T?irng reducing valve consists of a spool , a ball check valve,a slug, a load pistont two load plston springs, and a load piston orifice.In the application shown, the modulatlng reducing valve is part of a "valvestation.tr The additional components in a va,l-ve station include: an outercover, a select.or piston, and a decay orifice. Some modulating reducingvalves are equipped as shown with a pin in the center of the load pistonsprings; other valve groups do not have the pin.

OPERATION:mer start-rp, supply oil is always avall-able at the reducj-ng valvespool. Valve movement and clutch engagement cannot begin, however,until p1lot oi1 frorn the rotary selector spool moves the selectorpiston to the left. llovement of the selector piston accomplishes tvopurposes: (l) the drain passage at the decay orifi.ce is blocked, and(2) the load piston springs are eompressed.

Compressing the load pi-ston spr ings rnoves the reducing valve spoo-l tothe left against the force of the j-nner spring. This opens the supplypassage (fron the pump) and permits pressure oil to flow to the clutch.As the clutcir fil1s, pressure oil opens the ball check valve and fillsthe slug cnanber at the left end of the reducing valve spool. At thesane *.ine, oil flows through the load piston orj.fice and fills the chamberbetneen ihe end of tire load pi-ston and the selector piston. The loadpiston oriflce provides a pressure drop and time delay in the flow of oilto tlte ioad pistc-rn chamber. This helps control the rate of modulatlon.l'ril-i-ng the Load piston chamber is made possible wiren tire selector pistoncoL'ers tire irain p;rssagc at ti-re decay orifice.

Tite ciuicir pressure ancl the pri-.ssurc in the slug chanber increase at thes.r::re rrrte. Just atter t.he clutch j-s filled, the pressure irr the sLugcita:.',:er ::ioves tlre rerlucing v;ilve spr:rol to the right. This novernent restrictst:re.i.-;; of 1.lressurt', qil to ti-re clutch and briefly limits the irrcrease ofcLutc:: pressure. The pressure in the load piston ch;lrnber tllell moves titeLoau.;l-ston iurtirer to thrr 1eft. This increases tl're spring force and reopenstlte suppil' passage perntit ling tlre clrrLt:[r pres;r;ur(: to agai"n incrcase. Iliisc_!,cle continuesi until thc load piston iras rnoved courpleteLy lo Llre l.eIt-( aga in:; I tire stop) , Thc cltrtch pressllre is then at its nsxiululn se t titlg.Drrrir: :rodulatlon, t1:e retluciug valve spooL riloves lcl L ;tnd riiltrt wht.tc thrrIoatt pi-sLort rnLlves srntlotlrly tr; tittt Lcft,

,\s Liie - irrtt:ir prcssrlrr.l incrcases to naxinunt, the operation of valve $fatiolrstitat are equipped with;1. pin in the center of their load piston springs issli.;;iLi_r il i l ii:rent th;rn thc opr:r.ation of statiorrs that do rrot have p,irts. lleirrthe enci oi the modtrlation cyclc, the pin corrtacts the reducirrg valve spool ,

noves tire spool completely to the lef t, and opens the clutch passage tr.r

supply oi-l. At this point, modulation ends and the clutch pressure

65

->

4.

immediately increases to the maximurn, During the time that the clutch isengaged, the reduclng valve spool remains conpletely to the left (as

shown) and the clutch pressure ls equal to the system Pressure.

Valve stations.that do not have pins in the cent.er of thelr load pistonspri-ngs control" clutch pressure settings that are lower than the systempressure. At 1he end of the modulation cycle, the pressure in the slugchamber moves the reducing valve spool a small distance to the right torestrict the flolt of supply oll to the clutch. This is the "meteringpositiontt of the redueing valve spool. In this positicn, the valvenaintairrs precise eontrol of the clutch Pressure.

During a shtft, the pressure of a clutch being dlsengaged does rrotimrnecliatety drOp to uero, Instead, ttre clutch pressure decreases ata controlled rate, Clutch release (decay) is lnitlated when the pilotoil chamber at the rl-ght end of the selector piston is draincd' Thispermlts t.tre selector piston and the load pJ-ston to move to ttre right'CLutch pressure starts to decrease, but cannot drop to zeto until theehamber between the load piston and the selector piston is drained'The only way that oil can flow out of thls chamber is through the deeay

orifice wtrich waa uncovered when the selector piston moved to the right.As the load piston springs force the oll frorn the load piston chamber,the clutch pressure gradually decreases. lJhen the load piston hasmoved conpletely to the rtght, the clutch Pressufe is zero.

WHERE USED:An ,g'E!-_ed semiautquatic transmissions with individual clutch modulation(rGr)

66

TROUELESHOOTING

}IAI,FUNCTION POSSI3LN CAUSE CORRECTION

Clutch slips duringengagement

One or more clutehesdo not engage

Transmlsslon shiftsharshly

Lortr clutch pressuresetting

Partially restrictedload piston orifice

Pl1ot ptessure low orat zero

Restricted load pistonorifice

Reduclng valve spoolstuck closed

Selector piston stuckin bore

Load piston stuck inselector plston

tligh clutch pressuresettLng

Reducing valve spoolstuck open

A$just pressure setting(add shinrs) or replacespr ings

Clean or replace loadpiston orifice

Chbck operation 0fpriority reducing valveand neutralLzer valve;Check for partialrestrictlon of pi.lot oilsupply port and passage

Clean or replace loadpiston orifice

Free spool in valve body

Free selector pistonouter cover

Free load piston

Adjust pressur€ setting(remove shins) orreplace springs

Free spool in valve body

87

NOTES

68

fATERPILIAR'

SEBVO526

November, '19€i{l