6. PROCEDURE WHEN SERVICING.
The relief valve is sometimes prevented from operating correctly by lint, pipe scale or some other solid matter
lodging between the pressure control piston (82800) and its seat (962491. This results in fluctuating pressure or a
complete drop in pressure. Usually the condition can be remedied by starting the pump and then loosening the jam nut
170769] and backing off the adjusting screw (95932) counter-clockwise several turns. This relieves the pressure control
spring (96163; and often will allow the circulating oil to clean away the dirt. The relief valve adjustment should then be
turned back clockwise until the proper maximum pressure setting has been re-established. Relief valve setting may be
checked by blocking machine travel or oil circulation and testing with pressure gauge.
Should it be necessary to dismantle these valves do so by driving out the two dowel pins located either side of the
name plate. This procedure will release the plug, seal, spring and hydrostat valve from one side of the body and a plug,
seal and sleeve from the other. To remove the throttle spool remove first the small hex socket head screw releasing the
dial, then the name plate and finally the throttle. The relief valve portion of these units may be removed by turning off
acorn nut, loosening the Jam nut, turning out the adjusting screw and finally tilting the body so that the remaining portions
are allowed to drop out, After disassembly all parts should be thoroughly cleaned in an approved mineral oil solvent and
inspected for wear. Check operation of hydrostat within the sleeve. These parts are fitted to a very close tolerance,
however, the spool should have freedom of movement within the sleeve. Check the condition of the relief valve piston and
its seat. Continued operation may distort the mating faces of these parts preventing proper sealing action. if this has
happened, replace with new parts. At reassembly, replace all seals with new parts. All possible precautions should be
taken to prevent damage to the parts and to keep them clean.
7. DIAGNOSIS OF IMPROPER OPERATION.
The following chart lists the difficulties which may possibly be experienced with the flow control valves, and
indicates the probable cause and the suggested remedy. The trouble indicated in the chart may of course be due to
difficulty with other equipment in the hydraulic system. Refer also to pump maintenance data.
Relief Valve setting
Block machine travel or
not high enough.
oil circulation and test
with pressure gage.
Relief Valve sticking
Dirt under pressure
Pressure not being
adjusting ball. See
Section 6 above.
Relief Valve venting
Test venting circuit
(If one is used) by
blocking vent line
Aeration of oil due to
All return lines must
Noisy or erratic
low oil level or
return below oil level.
return line not dis-
See also pump service
charging below oil
Damaged Oil Seals.
Replace oil seal. See
Service Parts Drawings.
dial or pressure