TOPIC 2. CONTROL VALVE

TM 10-3930-644-14&P

TOPIC 2. CONTROL VALVE

A. DESCRIPTION

the same bodies from which they were removed.

Valve sections must be reassembled in the

The hydraulic control valve (Fig 2-1) contains two basic

same order.

plunger sections (lift and tilt controls; additional plunger

sections can be added for accessory unit control). Each

1. Remove the four tie studs and nuts and

of the sections may be replaced separately. All parts of

separate the valve sections. Be careful not to

the sections may be replaced individually, except the

destroy or lose spacers.

plunger section housings and their selectively fit

plungers, which must be replaced as units.

2. Remove the two screws which secure the spool

end cap and remove the cap (and switch

The function of the control valve is to direct the flow of

bracket, if used). If the cap has a detent

the hydraulic fluid, under pressure, to the appropriate

assembly, screw out the detent plug and remove

cylinders.

the spring and piston. Remove the O Ring from

the cap.

The control valve contains an adjustable relief valve

which protects the system against damage resulting

3. Slide the spool out of its bore and remove the O

from excessive pressure that builds up when the lift or tilt

Rings from the groove in the spool and from the

cylinders reach full stroke. Excessive pressure can also

valve body around the spool bore. Do not

result from overloads.

The relief valve should be

remove the centering spring, retainers or the

adjusted to unseat at i.950 50 psi.

spool extension unless it is necessary to replace

them.

The control valve requires very little attention with the

exception of keeping the hydraulic lines and hose

4. Grip the stem of the check valve plug with pliers

connections tight.

and pull it out of the valve body. Remove the O

Ring and back-up ring. Remove the spring and

B. REMOVAL

ball from the valve body.

The following procedure is recommended for proper

5. Screw out the plug which retains the relief valve

control valve removal:

and remove the O Ring from the plug. Remove

the spring and the relief valve sub-assembly.

1. Make sure lift is collapsed and that mast is tilted

Remove the solid plug.

all the way forward.

6. Remove the fitting. O Rings and back-up ring.

2. Disconnect control lever linkage if necessary to

gain access for control valve removal. (On

D. CLEANING, INSPECTION AND REPAIR

some new model trucks, the handles, linkage,

and mounting bracket can all be removed along

1. Discard all old seals. Wash all parts in a clean

with the control valve.)

mineral oil solvent and place them on a clean

surface for inspection.

3. Disconnect and cap all hydraulic lines.

2. Carefully remove by light lapping. Be certain

there is no paint or burring on mating surfaces of

NOTE

valve bodies.

Properly tag all lines so that they will

be reconnected to their proper ports.

3. Inspect the valve spools and bores for burrs and

4. Remove the mounting capscrews and control

scoring. If scoring is not deep enough to cause

valve.

objectionable leakage, the surfaces can be

polished with crocus cloth.

If scoring is

5. Clean outside of valve with a solvent and dry

excessive, the valve body and spool must be

with compressed air.

replaced. Check the valve spool for freedom of

movement in the bore.

6. Remove all fittings and place control valve in a

suitable work area.

4. Check the relief valve for smooth movement in

its bore. The valve should move from its own

C. DISASSEMBLY

weight.

During disassembly, particular attention should be given

E. REASSEMBLY

to identification of parts for reassembly. Spools are

NOTE

selectively fitted to valve bodies and must be returned to

Coat all parts with clean hydraulic oil

to facilitate assembly and provide

initial lubrication. Petroleum jelly can

be used to hold seal rings in place on

assembly.

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