GROVE Published 1-20-2017, Control# 483-02 4-13
CD5515-2/YB5515-2 SERVICE MANUAL HYDRAULIC SYSTEM
TELESCOPE CIRCUIT
Use the hydraulic schematic in Section 12 along with the
following text to understand how the telescope circuit
functions.
General
The telescope circuit includes the telescope cylinder, a
holding valve, ports 5 and 6 of the hydraulic swivel, an in-line
relief valve, an anti-double block cutout solenoid valve, the
first section of the four-spool main control valve, and the
hydraulic lines.
Oil Flow
Telescope Out
Pushing joystick away from operator connects the supply
from the pump to port B of the control valve section
(Figure 4-4). Oil leaves Port B and is routed through the anti-
double block solenoid valve and hydraulic swivel port 6 to the
holding valve on the base end of the cylinder to port E.
In the extending direction, oil flows freely through the holding
valve and into the base end of the cylinder. The cylinder
extends and pushes oil ahead of the piston through the rod
end port of the cylinder. The oil returns through swivel port 5
and Port A of the control valve. From here, the oil is routed
into the tank passage and returns through the return filter to
the hydraulic tank.
The anti-double block valve will shut off the oil supply to the
telescope cylinder in the event the hook block comes in
contact with the boom head. In this case the operator must
let out more wire on the main hoist before he can extend the
boom.
Telescope In
Pulling the joystick towards operator, routes oil out of valve
port A and through the port 5 of the hydraulic swivel to the
rod port (‘R’) of the holding valve mounted on the hydraulic
cylinder. The cylinder starts to retract but meets resistance
from the oil held in the cylinder base end by the holding
valve. This restriction causes an increase in pressure as the
pump continues to push more oil into the rod port of the
cylinder. When the pressure is high enough to open the
holding valve, the cylinder retracts. See Holding Valve.
The relief valve in the circuit protects the telescope cylinder.
If the pressure should ever reach 203.40 bar (2950 psi) to
the rod port or 193.05 bar (2800 psi) to the piston port the
relief valve will open and return oil to tank, stopping any
movement of the telescope cylinder and its cable
mechanism.
Oil from the rod end of the cylinder returns through port 6 of
the hydraulic swivel to the control valve. From here, the oil is
routed through the return filter to the hydraulic tank.
Holding Valve
The holding valve has three functions:
1. Inhibit cavitation of the cylinder.
2. Give full control of the lowering of the boom.
3. Hold the load in event of a hydraulic failure.
Pilot pressure from the rod side of the piston opens the
holding valve. If the cylinder starts to retract faster than the
pump can fill the cylinder, there will be a decrease in the pilot
pressure. The holding valve will close and interrupt the flow
of oil from the cylinder. The holding valve will interrupt the
flow as often as necessary to keep the cylinder filled. Also, if
there is a failure of the pump or a hydraulic line, the holding
valve will hold the boom in position.
Engine speed is important for smooth operation. At low
engine speed, normally there will not be enough oil from the
pump to keep the cylinder filled. As a result, the boom will
move down in a movement that is not regular.
Port Relief Valve
The port relief valve installed in the telescope circuit is used
to protect the telescope mechanism (cables, sheaves, etc.)
from damage caused by high hydraulic oil pressure.
The relief valve for the telescope circuit is located in the
telescope section of the four-section control valve and is
connected to Port B and Port A.
Checking Relief Valve Pressure
1. Install a 0 - 344.50 bar (0 - 5000 psi) pressure gauge on
the quick-coupler for pump section No.2.
2. Accelerate the engine to maximum RPM.
3. Fully retract the booms. Continue to hold the control in
position after the boom has stopped moving.
4. Read the pressure indicated on the pressure gauge
when the relief valve opens. It should be 134.45 ± 3.45
bar (1950 ± 50 psi).
5. Release the control lever.
6. Fully extend the booms. Continue to hold the control in
position after the boom has stopped moving.
7. Read the pressure indicated on the pressure gauge
when the relief valve opens. It should be 124.02 ± 3.45
bar (1800 ± 50 psi).
WARNING
Do not adjust the holding valve setting. The valve is
adjusted by the manufacturer.
Reference Only
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