TM 9-4940-568-34
3-3
3-2.
CRANE OVERVIEW
Chapter 3 contains maintenance instructions
for removing, replacing, repairing, installing
and adjusting components authorized by the
Maintenance Allocation Chart (MAC) at the
Direct Support Maintenance level.
3-3.
CRANE PRINCIPLES OF OPERATION
a.
General. The FRS crane is (hydraulically
powered, telescopic with auxiliary remote
controls. The FRS crane has the following four
main functions: boom, telescope, swing, and
hoist. The FRS crane is laterally supported by
outrigger beams and jack cylinders.
b.
Hydraulic System. The main controls
receive hydraulic oil supplied by the FRS
hydraulic system. The two-way solenoid valve
opens or blocks the passage of oil to the crane
control valves. When the solenoid valve is
activated by the remote control or the main
switch, hydraulic oil is diverted through the
main control valves. The solenoid valve
incorporates a manual override in the event of
electrical failure.
The main control valves are closed-center,
closed-port valves. Hydraulic oil always
passes through the unloader valve and returns
to the reservoir, unless one or more of the
control valves are activated. When a control
valve is activated, the ports open to direct
hydraulic oil to a function of the crane. The
control valve also sends a signal to the
unloader valve, regulating the return flow.
