Brake Holding Valve; Hydraulic Swivel; Swing Circuit; General - Manitowoc Grove CD3340B Service Manual

HYDRAULIC SYSTEM

Brake Holding Valve

The holding valve has three functions:
1. Inhibit cavitation of the motor.
2. Give full control of the lowering of the load.
3. Hold the load in event of a hydraulic failure.
Pilot pressure from the down stream side of the motor opens
the holding valve. If the motor starts to turn faster than the
pump can supply oil to the motor, there will be a decrease in
the pilot pressure. The holding valve will close and interrupt
the flow of oil from the motor. The holding valve will interrupt
the flow as often as necessary to keep the flow constant to
the motor. Also, if there is a failure of the pump or a hydraulic
line, the holding valve will hold the load 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 motor turning. As a result, the load will
move down in a movement that is not regular.
Do not adjust the holding valve setting. The valve is
adjusted by the manufacturer.

Hydraulic Swivel

See page 4-12 for hydraulic swivel information.

SWING CIRCUIT

General

The swing motor is controlled by the fourth section of the
four-spool control valve (Figure 4-4). In the neutral position,
oil is held in the circuit and the motor is prevented from
turning. The gear/pinion is protected by a port relief valve set
at 159.96 bar (2320 psi) in both swing directions.

Oil Flow

Swing Right
Pushing the joystick away from the operator sends oil
through motor port A of the valve section to the swing motor.
The motor rotates clockwise and causes the mast to rotate to
the right. Oil from downstream side of the motor returns
through the B port and sent back to tank through the return
filter.
Swing Left
Pulling the joystick towards the operator sends oil through
motor port B of the valve section to the swing motor. The
motor rotates counter clockwise and causes the mast to
4-18
WARNING
Published 04/07/2015 Control # 569-00
rotate to the left. Oil from downstream side of the motor
returns through the A port and is sent back to the tank
through the return filter.

PILOT CONTROL SYSTEM

General
The pilot control system is used to actuate the spools of the
main control valve using hydraulic pressure. The system
includes a relief valve, two remote control valves and the
hydraulic hoses and fittings.
Oil Flow
The pilot control system receives its hydraulic flow from the
pilot port of the Main Control Valve. The pilot control circuit is
protected by a 34.48 bar (500 psi) relief valve.
Oil under pressure is routed to the four remote control
valves, where it is directed by the remote control valves to
actuate the spools of the main control valve.
Oil from the remote control valves is routed back to the
hydraulic tank.

Pilot System Relief Valve

The relief valve maintains the 34.48 bar (500 psi) system
pressure by opening and returning oil to the hydraulic tank
when the pressure setting is exceeded.

PRESSURE SETTING PROCEDURES

Checking and Adjusting Hydraulic Pressure
Settings
Check all pressures with hydraulic fluid at normal operating
temperature, 60°-71°C (140°-160°F)—check hydraulic fluid
temperature at the bottom of the hydraulic tank. Also, the
engine must be at maximum RPM.
Pump Margin Pressure Setting
1. With the engine shut off, install pressure check
diagnostic quick disconnect (Parker PD240) with gauge
onto test nipple @ the G1 port (1, Figure 4-5).
2. Start engine and read the pressure gauge while at
engine idle. A reading of 24 ± 1.7 bar (350 ± 25 psi)
should be observed.
3. If pressure reading is correct, shut off the engine, and
disconnect the pressure gauge.
4. If pressure is incorrect, loosen the margin set screw from
the pump compensator valve (4, Figure 4-6).
5. Adjust the margin pressure setting by turning the margin
adjusting screw (1, Figure 4-6) until 24 ± 1.7 bar (350 ±
25 psi) pressure is obtained on the gauge; clockwise
CD3340B/YB4411