SUB-SECTION
4A
BASIC MACHINE WITH GEARMATIC MAIN AND AUX-
cylinder, however, is prevented from returning to the reser-
ILIARY WINCHES (100J3556)
voir by the counterbalance valve until sufficient pressure
from the rod end of the cylinder, supplied through a pilot
PUMPING CIRCUIT. The pumping circuit consists of the
line, is applied to the counterbalance valve. When enough
reservoir, pumps, swivel, return line filters and oil cooler.
pressure is developed in the pilot circuit, the counter.
balance valve will shift to the open position, allowing the
The hydraulic pumps are driven by the carrier engine
oil at the blind end of the cylinder to return to tank.
through a pump drive, which allows the pumps to be dis-
connected from the engine when the machine is being
BOOM TELESCOPE CIRCUIT. To extend the boom at low
roaded. When the pumps are driven, oil is drawn from the
speed, the operator pushes the control lever forward, to the
reservoir through the suction manifold and IS forced out
detent. In this position, hydraulic oil passes from the pump,
into the system. The oil leaving the pumps flows through the
through the control valve and the check valve in the
rotary joint, through the open center control valves, and
counterbalance valve, to the telescope cylinders. Oil from
then back to the reservoir through either the return line
the blind end of the telescope cylinders flows through a
filters or oil cooler.
50-50 flow divider and a priority flow control valve, and
then returns to tank through the control valve. These flow
The oil will continue to circulate through the system, as
control valves are used to synchronize the extension of the
long as all the control valves are in the neutral position.
boom sections by metering the flow of oil out of the cylin-
Under these conditions, very little pressure wiII be devel-
ders. Crossover relief valves are provided in the flow divider
oped, since there is practically no resistance to oil flow.
to divert the oil that the flow divider is not capable of
handling back to tank via an alternate flow path.
Oil flowing through the oil cooler comes from the return
side of the swing control valve. Oil returning from the re-
To extend the boom at high speed, the operator pushes the
maining control valves flows through the return line filters.
control lever past the detent. In this position, hydraulic oil
This arrangement ensures that all the return oil is either
enters and leaves the cylinders as described above. Instead
cooled or filtered before returning to tank.
of returning to tank, however, the oil passes through the
control valve and returns to the blind end of the cylinders.
BOOM HOIST CIRCUIT. To raise the boom, the operator
In this way, a relatively small amount of oil, represented by
pulls the control lever back. In this position, hydraulic oil
the difference between the volume of the blind and rod
parses from the pump, through the control valve and the
ends of the cylinder, is all that is required to extend the
check valve in the counterbalance valve, to the boom hoist
cylinder rod. This reduces the force applied to the boom
cylinders. Since the oil flowing to the cylinders is blocked
sections by the cylinders, but increases the speed of opera-
by the velocity fuse on each cylinder, no cylinder move-
tion.
ment will occur until the pressure in the circuit is sufficient
to shift the velocity fuse spool to the open position. When
To retract the boom, the operator pulls the control lever
this occurs. the oil from the control valve will flow past the
back. In this position, hydraulic oil is fed directly to the rod
velocity fuse spoof and check valve to the blind end of the
end of the cylinder through the priority flow control valve
cylinder, causing the cylinder to extend and lift the boom.
and 50-50 flow divider. The priority flow control valve
meters the oil to the circuit, which is then divided into two
NOTE
equal flows by the 50-50 flow divider. Oil flowing to the
rod end of the cylinder also applies pressure to the counter-
Once the velocity fuses are shifted to the open posi-
balance valve, opening the valve to allow the oil to return to
tion, the spool will remain in the open position as
tank through the control valve.
long as pressure is trapped in the circuit. If pressure is
lost, the spool will shift to the closed position and the
boom will lower slowly as the oil in the cylinders is
SWING CIRCUIT. When the operator moves the swing lever
vented to atmosphere through the orifices in the
to either the forward or backward position, hydraulic oil is
valve.
directed through the control valve to the swing motor.
To lower the boom, the operator pushes the control lever
This causes the swing pinion, which is mated to the slewing
forward. In this position, hydraulic oil is fed directly to the
ring gear, to rotate and turn the upper in relationship to the
rod end of the cylinder. The oil at the blind end of the
lower.
