CONTROL VALVE - TM-10-3930-644-14-P0131

TM 10-3930-644-14&P

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J. CHECKING CONTROL VALVE INLET PRESSURES

regarding the nature of the breakdown.

In some cases where a pump is inoperative, it may be

possible to repair it in the field. Satisfactory repair can

be accomplished, provided a clean, well equipped repair

shop manned by a competent mechanic is available.

I. CONTROL VALVE

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

the hydraulic oil, under pressure, to the appropriate

cylinders. The control valve requires very little attention

with the exception of keeping the hydraulic lines and

hose connections tight.

There are normally, two operating plungers in the valve.

One is a single acting plunger which operates the lift

cylinder. The other is a double acting plunger : o

operate the tilt cylinders.

When the control lever is in "neutral" position, the oil is

being circulated through the open center of the valve

and back to the reservoir; but is not entering any of the

Figure 1-4. Relief Valve

cylinder ports. As the control lever is moved to its

operating position, the cylinder ports begin to open and

1. Relief Valve Adjustment

the open center passage begins closing. At the extreme

limit of control lever travel, the cylinder ports are open

Whenever the control valve or hydraulic pump

and the open center passage is closed. The applied oil

has been repaired or replaced, check the relief

pressure then opens the check valve and allows the oil

valve and adjust to open at specified pressure.

to flow to and/or from the lift or tilt cylinders.

Check and adjust the relief valve (Fig i-4)

located in the lift section of the control valve as

An adjustable relief valve is Incorporated in the control

follows:

valve. It is used to relieve extreme pressures when

maximum tilt or lift position, or overloads are reached, to

a. Gain access to the control valve; actual

prevent damage to the hydraulic system.

location varies between truck models.

1. Linkage

b. Some adapters nave a plug in them where

a pressure gauge can be installed. If unit

Improperly adjusted or out of adjustment linkage

is not equipped with this type adapter.

can result in binding or bending of the control

Disconnect the hydraulic line at the inlet

valve linkage.

port of the control valve.

Ensure that tilt and lift control levers and

c. Install a tee fitting on the end of the

associated linkage travels freely and smoothly

hydraulic line and connect the tee fittings

through forward and backward movement of

to the adapter in the inlet port.

each lever and that the control valve plungers

respond accordingly. Adjust, repair or replace

d. Install a pressure gauge with a 0 to 3000

as is necessary.

psi range in the tee.

Be certain that pivot points or other mating

e. Place shift lever in neutral position, turn

surfaces are free of accumulated sludge and

key switch ON and start engine.

remain lightly lubricated to function smoothly.

f. the tilt lever back to retract the tilt

cylinders and hold lever in this position.

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