JLG 500RTS ANSI Service Manual - Manual (Page 20)

SECTION 2 - PROCEDURES
2-4 – JLG Sizzor – 3120696
failure of the system pump is also avoided by relieving cir-
cuit pressure. The relief valve is installed in the circuit
between the pump outlet (pressure line) and the cylinder
of the circuit, generally as an integral part of the system
valve bank. Relief pressures are set slightly higher than
the load requirement, with the valve diverting excess
pump delivery back to the reservoir when operating pres-
sure of the component is reached.
Crossover Relief Valves
Crossover relief valves are used in circuits where the actu-
ator requires an operating pressure lower than that sup-
plied to the system. When the circuit is activated and the
required pressure at the actuator is developed, the cross-
over relief diverts excess pump flow to the reservoir. Indi-
vidual, integral reliefs are provided for each side of the
circuit.
2.6 COMPONENT FUNCTIONAL
DESCRIPTION
Piston Hydraulic Pump
The Sundstrand piston hydraulic pump is attached to and
driven by the gasoline or diesel engine. The pump is a 2.8
in 3 (45.9 cm 3 ) displacement piston pump that powers the
drive motors.
Gear Hydraulic Pump
The John Barnes gear pump is piggy-backed to the piston
pump, and operates all machine functions except drive.
The gear pump has a displacement of 0.6 in
3
(10.5 cm
3
).
Manual Descent Valve (If Equipped)
The manual descent valve is located on top of the holding
valve on the lift cylinder. The holding valve is a normally
closed solenoid valve, and holds the platform in place
when raised. When activated, the valve opens to permit lift
down. The holding valve is connected to the manual
descent valve, which is connected to a cable which, when
pulled, manually opens the lift down port of the valve and
allows the platform to be lowered in the event hydraulic
power is lost.
2.7 SLIDING WEAR PADS
The original thickness of the sliding pads is 3.5 in (90
mm). Replace sliding pads when worn to 3.3 in (83 mm).
2.8 PUMP COUPLING LUBRICATION
To insure proper operation and a long service life for the
Hayes pump coupling, it is necessary to lubricate the
splines of the coupling any time the coupling is disassem-
bled or replaced. Lubricate the splines with Texaco Code
1912 Pump Coupling Grease ONLY. No other lubricant is
recommended.
2.9 CYLINDER CHECKING PROCEDURES
NOTE: Cylinder checks must be performed any time a cylin-
der component is replaced or when improper system
operation is suspected.
Cylinder w/o Counterbalance Valves - Steer
Cylinder, Platform Ext. Cylinder, Axle
Lockout Cylinder (If Equipped)
NOTICE
OPERATE FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system and fully extend cylinder to be
checked. Shut down hydraulic system.
2. Carefully disconnect hydraulic hose from retract port
of cylinder. There will be initial weeping of hydraulic
fluid which can be caught in a suitable container.
After the initial discharge, there should be no further
leakage from the retract port.
3. Activate hydraulic system and activate cylinder
extend function. Check retract port for leakage.
4. If cylinder leakage is 6-8 drops per minute or more,
piston seals are defective and must be replaced. If
cylinder retract port leakage is less than 6-8 drops
per minute, carefully reconnect hose to retract port
and retract cylinder.
5. With cylinder fully retracted, shut down hydraulic
system and carefully disconnect hydraulic hose
from cylinder extend port.
6. Activate motor and activate cylinder retract function.
Check extend port for leakage.
7. If cylinder leakage is 6-8 drops per minute or more,
piston seals are defective and must be replaced. If
extend port leakage is less than 6-8 drops per
minute, carefully reconnect hose to extend port,
then activate cylinder through one complete cycle
and check for leaks.
Cylinders w/Single Counterbalance Valves -
Lift Cylinder, Leveling Jacks (If Equipped)
1. Using all applicable safety precautions, activate
hydraulic system.