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NOTE: If relief valve or hoist valve assembly has
been replaced or rebuilt, hoist relief valve pressure
should be checked.
Relieve pressure before disconnecting hydraulic
lines. Tighten all connections securely before
applying pressure.
Hydraulic fluid escaping under pressure can
have sufficient force to enter a person's body by
penetrating the skin and cause serious injury and
possibly death if proper medical treatment by a
physician familiar with this type of injury is not
received immediately.
Hoist System Relief Pressure Adjustment
1. Install two 0-35,000 kPa (0-5000 psi) pressure
gauges (one to each diagnostic coupler located
at each outlet port on the hoist pump).
2. Start engine and run at low idle.
Pressure at both hoist pumps should be
approximately 517 kPa (75 psi) or less with
oil temperature at 29°C (70°F).
3. To allow full extension of the hoist cylinders, dis-
connect the hoist up limit solenoid from the wir-
ing harness located in the hydraulic cabinet
behind the operators cab.
Be sure there is adequate (safe) overhead clear-
ance before raising body to full up position.
L10-16
CHECKING HOIST SYSTEM PRESSURES
Hydraulic Check-out Procedure
4. With engine at low-idle, place hoist lever in
power up position and hold until body is in the
full raised position.
Pressure at both hoist pumps should be
17,237 ± 690 kPa (2500 ±100 psi).
NOTE: Each hoist pump section supplies oil to a
separate inlet section on the hoist valve. Each inlet
section on the hoist valve contains a power up relief
valve. If the either relief pressure is not within
specifications, adjust or replace the respective relief
valve.
5. If power up relief pressure is not correct, adjust
pressure as follows:
a. Move hoist control lever to the "power down"
position and allow body to completely rest on
frame rails. Shut down engine.
b. Relieve all hydraulic pressure from hoist sys-
tem.
NOTE: One relief valve is located under each inlet
valve cover.
c. Remove small external tube and cap screws
(1, Figure 10-6) from inlet section cover (2)
where the relief valve needs serviced.
Remove cover from hoist valve and spring
(3) from relief valve.
d. Loosen jam nut on relief valve (4) and turn
screw in (clockwise) to increase pressure or
out (counter-clockwise) to decrease pres-
sure.
L10028
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