National Crane Published 10-30-2014 Control # 040-09 5-43
1400H OPERATOR AND SERVICE MANUAL SERVICE
HYDRAULIC SYSTEM
The hydraulic system of this machine is an open center
type, consisting of a fixed displacement three section high
pressure pump which supplies oil to a two inlet main control
valve and a one inlet turn/outrigger/ stabilizer control valve.
The hydraulic oil is supplied by a truck mounted oil
reservoir and is equipped with replaceable canister type
return oil filters. The truck power take off driven hydraulic
pump is sized to supply 32 gpm (121 lpm) to the hoist circuit,
32 gpm (121 lpm) to the boom lift and telescope circuits, and
16 gpm (61 lpm) to the turn and outrigger circuits at 2,000
rpm pump/pto shaft speed. Higher pump speeds may result
in excessive heat generation in the hydraulic system. The
pump rotation direction is reversible. Consult pump manual
for changing rotation direction if necessary to match PTO
output direction.
The main control valve is equipped with two inlet
sections and one mid-outlet section. One inlet supplies oil
from the front (shaft end) section of the pump to the hoist
function(s). The other inlet section distributes flow from the
middle pump section to the boom and telescope functions.
Return oil is routed thru various outlet ports on the main
control valve. The main control valve contains inlet section
relief valves or port reliefs which limit pressure in the
hydraulic system to acceptable levels and control crane
movements. See specification section for proper pressure
settings.
The turn, outrigger and stabilizer functions are controlled
by a separate control valve. Oil from the rear section of the
pump is routed to the main inlet of the valve. The control
valve contains inlet section relief valves which limit pressure
in the hydraulic system to acceptable levels and control
crane movements. See specification section for proper
pressure settings.
The crane hydraulic system includes a rated capacity
limiter (RCL) system. This system monitors lift cylinder
pressure. As the pressure in the lift cylinder approaches a
maximum predetermined level, which can be monitored on
the RCL display console, a signal is sent to a solenoid which
dumps oil flowing to crane functions which increase the over
capacity condition.
All load bearing cylinders on this machine are protected
from inadvertent movement or collapse due to hose failure
by pilot operated check valves or by pilot operated
counterbalance valves if overhung loads must be controlled.
The standard swing gearbox is locked in place by an
integrally mounted spring applied brake and a dual
counterbalance motor holding valve. The swing brake and
counterbalances are piloted open and closed by operating
swing left or right and are automatically reapplied by ceasing
the swing function. Maximum swing speed can be limited
using the swing speed adjustment valve.
See “Specifications” section for system pressures and
flows.
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