To retract the boom, the operator pulls the control levers
BASIC MACHINE WITH P&H MAIN AND AUXILIARY
back. In this position, hydraulic oil is fed directly into the
rod end of the cylinders. At the same time, pilot pressure
PUMPING CIRCUIT. The pumping circuit consists of the
from the line is applied to the counterbalance valve,
reservoir, pumps, swivel, return line filters and oil cooler.
opening the valve and allowing the oil to return from the
blind end of the cylinder, through this valve and the control
The hydraulic pumps are driven by the carrier engine
valve to tank.
through a pump drive, which allows the pumps to be dis-
connected from the engine when the machine is being
SWING CIRCUIT. Hydraulic oil, under pressure, is deliv-
roaded. When the pumps are driven, oil is drown from the
ered by the swing pump to the swing control valve through
reservoir through the suction manifold and is forced out
the priority flow control valves. The hydraulic oil will
into the system. The oil leaving the pumps flows through the
continue to circulate and no motion will occur until
rotary joint, through the open center control valve, and
the operator moves the swing lever to either the forward
then back to the reservoir either through the return line
or backward positions.
filters or oil cooler.
When the operator moves the swing lever to either the for-
The oil will continue to circulate through the system, as
ward or backward position, hydraulic oil is directed
long as all the control valves are in the neutral position.
through the control valve to the swing motor. This causes
the swing pinion, which is mated with the slewing ring
Under these conditions, very little pressure will be devel-
gear, to rotate, thereby turning the upper in relation to the
oped, since there is practically no resistance to oil flow.
Oil flowing through the oil cooler comes from the return
The swing brake is used to lock the swing reducer so that
side of the swing control valve. Oil returning from the re-
the swing motor cannot turn, thus preventing the upper
maining control valves flows through the return line filters.
This arrangement ensures that all the return oil is either
cooled or filtered before returning to tank.
BOOM HOIST CIRCUIT. To raise the boom, the operator
The upper of the machine will swing freely if the
pulls the control lever back. In this position, hydraulic oil
swing brake is not applied.
passes from the pump, through the control valve and the
check valve in the counterbalance valve on the boom hoist
The swing brake is shown in the released position. When the
cylinder, to the blind end of the cylinder. Fluid from the
operator depresses the swing brake pedal, the hydraulic oil
rod end of the cylinders returns to the reservoir through the
in the brake chamber is returned to tank, and the brake
springs set the brake. Releasing the brake pedal, allows
To lower the boom, the operator pushes the control lever
hydraulic oil to enter the brake chamber, thereby releasing
forward. in this position, hydraulic oil is fed directly into
the rod end of the cylinders. At the same time, pilot pres-
The swing brake lock is shown in its normal operating posi-
sure from the line is applied to the counterbalance valve,
tion. When the machine is not working or is shut down, the
opening the valve and allowing the oil at the blind end of
swing brake lock should be pieced in the locked position. in
the cylinder to return to tank through this valve and the
this position, the oil in the brake chamber is returned to
tank and the brake is applied.
BOOM TELESCOPE CIRCUIT. To extend the boom, the
MAIN WINCH CIRCUIT. The main winch control valve
operator pushes the control levers forward. In this position,
directs hydraulic oil from the pump to one winch motor
hydraulic oil passes from the pump, through a one to one
port or the other. This will cause the winch to turn in a
flow divider to the control valve. From the control valves,
direction which will lift or lower the load, depending upon
the oil passes through the check valve in the counterbalance
which side of the motor the hydraulic pressure is applied.
into the blind end of the cylinders.