SUBSECTION 5D
HYDRAULIC COMPONENTS
GENERAL
4. The valve can now be removed.
This subsection contains the information necessary to re-
REPAIR AND ADJUSTMENT. The valve may be repaired by
pair the hydraulic components other than the control
replacing the individual components. All the subassembly
valves.
valves are nonadjustable and non-repairable except the
pressure unloading valve.
GENERAL REMOVAL
The relief valve has been adjusted at the factory and should
Prior to removing any of the components in this section shut
retain its setting over extended periods of time, under nor-
down the engine and remove the battery ground cable to
mal conditions. The relief valve spring will eventually
prevent operation of the machine while the item is being
weaken with machine use, however, so periodic checking
serviced. Operate the controls to relieve all pressure in the
of the relief valve setting is recommended.
system and also clean the area around the item being re-
moved to prevent the entry of contaminants.
To check the setting on the relief valve, proceed as follows:
COMBINATION CONTROL VALVE (36Q327)
DESCRIPTION. The combination control valve serves two
functions (three if the machine is equipped with side frame
The pressure setting of 3000 psi must not be
extension). The primary function is to relieve system pres-
changed. Any attempt to change the setting
sure and maintain it at a preset maximum. Hydraulic pump
will void any and all guarantees, expressed or
flow is diverted back to tank when the pressure setting is
implied.
reached.
1. Operate the machine until the hydraulic oil temperature
Secondly, it serves as an unloading valve to keep system
is a minimum of 70F. Shut the engine down and reduce hy-
pressure within preset limits. Pump pressure is used to
draulic pressure to zero.
charge up the accumulator, which acts as a pressure stor-
age reservoir. When a preset upper pressure is reached the
2. Obtain an accurate 0 to 5000 psi pressure gauge.
unloading valve directs the pump flow back to the reservoir
3. Connect the flexible hoses to the crawler extension and
at atmospheric pressure. Each time a hydraulic valve is op-
retraction controls.
erated, oil from the accumulator is used and system pres-
sure begins to fall until a preset low limit is reached. At this
4. Place the upper-lower diverter switch in the "lower" po-
point, the unloading valve will direct the flow of oil from the
sition.
pump to the accumulator to recharge the system.
5. Install a pressure gauge in the pressure gauge port of the
The third function of this valve is to act as a directional con-
tee fitting installed as shown in the insert of Figure 5D-1.
trol device (diverter) to direct pump pressure to the side
6. Increase engine speed to approximately 1400 rpm at no
frame extension circuit. This is done through an electri-
load.
cally operated solenoid.
7. Fully retract one crawler side frame and observe the
REMOVAL. Ordinarily there is no reason to remove this
pressure gauge to determine the point at which the relief
valve as all maintenance may be done by removing and re-
valve opens. The relief should open at approximately 3000
placing the individual components. If it becomes necessary
psi. The pressure gauge will instantly show a drop of pres-
to remove the valve, proceed as follows (see Figure 50-1):
sure at the point when the relief valve opens.
1. See General Removal at the beginning of the section.
8. If the relief valve does not function as described in step 7,
2. Disconnect the hydraulic lines and electrical connec-
remove and replace the valve with a new one. Repeat steps
tion at the valve and position the lines to avoid interference
6 and 7 to test the new relief valve for proper operation.
as the valve is removed. Cap the lines to prevent the entry of
The unloading valve section of the combination control
valve is actually made up of two valves: The pressure un-
3. Remove the two capscrews and lockwashers attaching
loading valve and the priority flow regulator valve. Only the
the valve to the hydraulic units panel.
former can be adjusted.
5D-1
