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 TM 55-1925-273-10-1
0039 00
CRANE
During operation under usual conditions, the crane is powered by the central hydraulic system.
Supply and return flow for the crane passes through a swivel (figure 10, item 1) before arriving at the control valve bank
(figure 10, item 2). The swivel permits hydraulic fluid to flow to and from the crane's controls as the crane rotates.
The control valve bank (figure 10, item 2) is made up of a relief valve (figure 10, item 3), directional control valves for the swing
(figure 10, item 4), telescope (figure 10, item 5), winch (figure 10, item 6), and luffing (figure 10, item 7) functions. The relief
valve is set for 2650 PSI (183 bar) and prevents overpressurization of the crane's hydraulic components. The directional control
valves are all manually operated via control handles. These directional control valves control the direction and volume of
hydraulic fluid flowing to the swing motors (figure 10, item 8), the telescope cylinder (figure 10, item 9), the winch motor (figure
10, item 10), and the luffing cylinder (figure 10, item 11).
The swing motors (figure 10, item 8) are protected by a double counterbalance valve (figure 10, item 12) and by two flow
control valves (figure 10, item 13). The double counterbalance valve prevents the swing motors from turning unless hydrau-
lic pressure is applied to rotate them. The double counter balance valve also prevents a load from overriding the swing
motors and swinging the boom uncontrollably. The flow control valves, each set for 9 gal/min (34 L/min), prevent the boom
from swinging too quickly.
The swing motors (figure 10, item 8) are also provided with fail safe brakes (figure 10, item 14). These brakes are spring-
applied, and pressure-released and provide the primary braking method for the swing system.
Both the telescope (figure 10, item 9) and luffing cylinders (figure 10, item 11) are equipped with holding valves (figure 10,
item 15). The holding valves prevent the telescope and luffing cylinders from retracting until pressure is supplied to the rod
side of the cylinder. When no pressure is applied to the rod side of the cylinder, a check valve (figure 10, item 16) inside the
holding valve prevents return hydraulic fluid from exiting the piston side of the cylinder. If this return hydraulic fluid cannot
exit, the cylinder cannot retract. When pressure is applied to the rod side of the cylinder, a portion of this pressure is routed
through the internal pilot line to open the holding valve. Once the holding valve is OPEN, return flow is permitted from the
piston side of the cylinder, and retraction occurs.
The winch motor (figure 10, item 10) is also equipped with a holding valve (figure 10, item 17). This valve operates just like
the holding valve described above, except that it prevents return flow from the winch motor when the motor is operating in
the LOWER direction. This prevents the load from overrunning the motor and causing uncontrolled lowering of the load.
The winch motor is also fitted with a fail safe brake. Like the winch motor brakes, this brake is spring-applied and pressure-
released, and provides the primary braking method for the winch.
0039 00-16
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