JLG 740AJ Service And Maintenance Manual page 446

SECTION 5 - BASIC HYDRAULIC INFORMATION AND SCHEMATICS
DIAGRAM ACTION STEP COMMENTS
1. Inspect External Control Linkage for:
a. Misadjusted or disconnected
b. Binding, bent or broken
2. Inspect Control Valve for:
a. Plugged control orifice(s)
b. Damaged mounting gasket
c. Misadjusted, damaged or broken neutral return
spring
d. Broken control connector pin
e. Faulty destroke valve (if used)
f. Galled or stuck control spool
g. Neutral detent or lockout switch misadjusted (if
used)
3. Inspect System Relief Valves for:
a. Improper pressure relief setting
b. Damaged or broken spring
c. Valve held off seat
d. Damaged valve seat
4. Inspect Servo Piston for:
a. Misadjusted, damaged or broken neutral return
spring assembly
b. Galled or stuck servo piston
c. Damaged or missing o-ring and/or backup ring
5. Check Oil Level in Reservoir:
a. Consult owner/operators manual for the proper
type fluid and level
6. Inspect Heat Exchanger for:
a. Obstructed air flow (air cooled)
b. Obstructed water flow (water cooled)
c. Improper plumbing (inlet to outlet)
d. Obstructed fluid flow
7. Inspect Heat Exchanger Bypass Valve for:
a. Improper pressure adjustment
b. Stuck or broken valve
8. Inspect Bypass Valve for: (if used)
a. Held in a partial or full open position
9. Inspect Inlet Screen or Filter for:
a. Plugged or clogged screen or filter element
b. Obstructed inlet or outlet
c. Open inlet to charge pump
5-102
10. Check System Pressure:
a. See Figure 5-145. for location of pressure gauge
installation
b. Consult owner/operators manual for maximum sys-
tem relief valve settings
11. Check Charge Pressure:
a. See Figure 5-145. for location of charge pressure
gauge installation
b. Consult owner/operators manual for maximum
charge relief valve settings
12. Inspect Charge Relief Valve for:
a. Improper charge relief pressure setting
b. Damaged or broken spring
c. Poppet valve held off seat
13. Inspect Motor for:
a. Consult owner/operator manual for motor opera-
tion and trouble shooting
14. Inspect Charge Pump for:
a. Broken or missing drive key
b. Damaged or missing o-ring
c. Excessive gerotor clearance
d. Galled or broken gerotor set
System/Charge Relief Valve Pressure Settings
Inlet Vacuum
Case Pressure
Charge Pressure 250 to 300 psi (17.24 to 20.68 bar)
System Pressure 5000 psi (345 bar) maximum
3000 psi (207 bar) continuous
The high pressure relief valves are all factory preset and can-
not be readjusted.
The pressure setting is stamped on each valve with a three
digit number. To identify, multiply the noted number by 10 to
get the valves pressure setting.
Example: 10 x 500 = 5000 psi (345 bar)
2.94 psi (0.203 bar) max.
25 psi (1.7 bar) maximum
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