HYDRAULIC SYSTEM
CD5515-2/YB5515-2 SERVICE MANUAL
4-14
Published 1-20-2017, Control# 483-02
8.
If the pressure readings are correct, stop the engine and
remove the pressure gauge.
9.
If the pressure readings are incorrect, adjust the
pressure setting of the relief valve.
Telescope Cylinder Leakage Test
If the cylinder does not hold the load, the problem is normally
internal leakage in the cylinder. This problem can also be
caused by leakage in the control valve or the holding valve.
To check for leakage in the cylinder:
1.
Raise the boom a little above the horizontal position.
2.
Fully extend the boom.
3.
Stop the engine. Move the control lever several times in
each direction to release any hydraulic pressure in the
circuit.
4.
Disconnect the hydraulic hose from bulkhead elbow
Figure 4-7 which connects to the rod port of the
telescope cylinder. A little oil will drain from the elbow.
5.
Start the engine. Actuate the control lever in the direction
to extend the boom. Check the amount of leakage from
the bulkhead elbow. If the leakage is more than a few
drops per minute, replacement of the piston seals is
necessary.
Hydraulic Swivel
See page 4-9 for hydraulic swivel information.
HOIST CIRCUIT
Use the hydraulic schematic in Section 12 along with the
following text to understand how the hoist circuit functions.
General
The hoist circuit includes the hoist motor, a brake, a brake
holding valve, ports 1 and 2 of the hydraulic swivel, an anti-
double block solenoid valve, the control valve (Figure 4-4)
and the hydraulic lines.
Oil Flow
When the valve spool is in the neutral position, both A and B
ports are closed. Oil is held in the hoist circuit, inhibiting
movement of the hoist motor.
Hoist Up
Pulling the joystick towards the operator routes oil from the
pump to cylinder port A of the control valve (Figure 4-4).
From here the oil is routed through the anti-double block
solenoid valve, and swivel port 2 to the brake holding valve.
In this direction, the oil flows freely through the brake holding
valve to the hoist motor.
During this operation the brake is not released, since the
load is driven through a one-way cam clutch in the hoist,
bypassing the brake. When the hoist comes to a stop, the
cam clutch locks up and the load is prevented from moving
by the brake.
The anti-double block solenoid valve will shut off the oil
supply to the hoist motor in the event the hook block comes
in contact with the boom head. In this case the operator must
lower the hook block before the boom can be raised or
extended.
The oil turns the motor and returns through swivel port 1 to
the control valve. From here, the oil is sent back through the
filter to the hydraulic tank.
Hoist Down
Pushing the joystick away from the operator sends oil from
cylinder port B of the single spool control valve though swivel
port 1 to the hoist motor. The motor starts to turn, and the
increase in pressure on the up stream side of the motor
causes the brake holding valve to open and also the hoist
brake to disengage. The oil then returns through swivel port
2 to the control valve and back to the tank.
Drain Line
A drain line is connected to the hoist motor and returns drain
oil from the motor through swivel port 7 back to the hydraulic
tank.
Reference Only
