rod end of the cylinder. The oil at the blind end of the
cylinder, however, is prevented from returning to the reser-
voir by the counterbalance valve until sufficient pressure
BASIC MACHINE WITH GEARMATIC MAIN WINCH
from the rod end of the cylinder, supplied through a pilot
line, is applied to the counterbalance valve. When enough
pressure is developed in the pilot circuit, the counter-
PUMPING CIRCUIT The pumping circuit consists of the
balance valve will shift to the open position, allowing the
reservoir, pumps, swivel, return line filters and oil cooler.
oil at the blind end of the cylinder to return to tank.
The hydraulic pumps are driven by the carrier engine
through a pump drive, which allows the pumps to be dis-
BOOM TELESCOPE CIRCUIT. To extend the boom at low
connected from the engine when the machine is being
speed, the operator pushes the control lever forward, to the
roaded. When the pumps are driven, oil is drawn from the
detent. In this position, hydraulic oil passes from the pump,
reservoir through the suction manifold and is forced out
through the control valve and the check valve in the
into the system. The oil leaving the pumps flows through
counterbalance valve, to the telescope cylinders. Oil from
the rotary joint, through the open center control valves, and
the blind end of the telescope cylinders flows through a
then back to the reservoir through either the return line
50-50 flow divider and a priority flow control valve, and
filters or oil cooler.
then returns to tank through the control valve. These flow
control valves are used to synchronize the extension of the
The oil will continue to circulate through the system, as
boom sections by metering the flow of oil out of the cylin-
long as all the control valves are in the neutral position.
ders. Crossover relief valves are provided in the flow divider
Under these conditions, very little pressure will be devel-
to divert the oil that the flow divider is not capable of
oped, since there is practically no resistance to oil flow.
handling back to tank via an alternate flow path.
Oil flowing through the oil cooler comes from the return
To extend the boom at high speed, the operator pushes the
side of the swing control valve. Oil returning from the re-
control lever pest the detent. In this position, hydraulic oil
maining control valves flows through the return line filters.
enters and leaves the cylinders as described above. Instead
This arrangement ensures that all the return oil is either
of returning to tank, however, the oil passes through the
cooled or filtered before returning to tank.
control valve end returns to the blind end of the cylinders.
In this way, a relatively small amount of oil, represented by
BOOM HOIST CIRCUIT. To raise the boom, the operator
the difference between the volume of the blind and rod
pulls the control lever back. In this position, hydraulic oil
ends of the cylinder, is all that is required to extend the
passes from the pump, through the control valve and the
cylinder rod. This reduces the force applied to the boom
check valve in the counterbalance valve, to the boom hoist
sections by the cylinders, but increases the speed of opera-
cylinders. Since the oil flowing to the cylinders is blocked
by the velocity fuse on each cylinder, no cylinder move-
ment will occur until the pressure in the circuit is sufficient
To retract the boom, the operator pulls the control lever
to shift the velocity fuse spool to the open position. When
back. In this position, hydraulic oil is fed directly to the rod
this occurs, the oil from the control valve will flow past the
end of the cylinder through the priority flow control valve
velocity fuse spool and check valve to the blind end of the
and 50-50 flow divider, The priority flow control valve
cylinder, causing the cylinder to extend and lift the boom.
meters the oil to the circuit, which is then divided into two
equal flows by the 50-50 flow divider. Oil flowing to the
rod end of the cylinder also applies pressure to the counter-
balance valve, opening the valve to allow the oil to return to
Once the velocity fuses are shifted to the open posi-
tank through the control valve.
tion, the spool will remain in the open position es
long as pressure is trapped in the circuit. If pressure is
lost, the spool will shift to the closed position and the
SWING CIRCUIT. When the operator moves the swing lever
boom will lower slowly as the oil in the cylinders is
to either the forward or backward position, hydraulic oil is
vented to atmosphere through the orifices in the
directed through the control valve to the swing motor.
This causes the swing pinion, which is mated to the slewing
To lower the boom, the operator pushes the control lever
ring gear, to rotate and turn the upper in relationship to the
forward. In this position, hydraulic oil is fed directly to the