JLG H340AJ Service And Maintenance Manual page 162

Problem
4. Selected position cannot be main-
tained
3121634
Table 4-1. Troubleshooting
Cause
a. Control or counterbalance valve has
internal leak
b. Piston and/or shaft seal leak
c. Air in actuator
SECTION 4 - BOOM & PLATFORM
Solution
a. Disconnect hydraulic lines and bypass
valve. Leave valve ports open and operate
the actuator through housing ports (do not
exceed OEM's operating pressure). The
valve must be replaced if a steady flow of
fluid is seen coming from the valve ports.
b. Remove the plug and the housing's valve
ports. Operate the actuator through the
housing ports. Conduct the internal leak-
age test as described in the Testing section
on page 24 of this manual.
c. Purge air from actuator. See bleeding
procedures
4-45