Manitowoc Grove YB5515-2, Руководство по обслуживанию и ремонту

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GROVE
Published 1-20-2017, Control# 483-02
4-11
CD5515-2/YB5515-2 SERVICE MANUAL HYDRAULIC SYSTEM
4
block cutout solenoid valve, a valve section of the four-spool
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 and oil is held in the circuit to prevent
movement of the lift cylinders.
Raising the Booms
Pulling the joystick towards the operator connects the pump
passage A in the control valve. Oil leaves Port B of the
control valve section and passes through Port 4 of the
hydraulic swivel and enters the base end of the lift cylinders
through the holding valves. In this direction, the oil flows
freely through the holding valves and into the base end of the
cylinder. The cylinder rod starts to extend, pushing oil ahead
of the piston out the rod end port. The oil returns through Port
3 of the hydraulic swivel to Port A of the control valve section.
From here, the oil is routed to the tank passage of the control
valve assembly and returns through the return filter to the
hydraulic oil tank.
The anti-double block valve will shut off the oil supply to the
cylinders in the event the hook block comes in contact with
the boom head. In this case, the operator must let out more
rope on the hoist before the boom can be raised.
Lowering the Booms
Pushing the joystick away from the operator sends oil in the
opposite direction and causes the cylinder to retract. The
holding valve lets the cylinder retract only if there is oil under
pressure available to the rod port of the cylinder. See Holding
Valve.
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 good lowering of the boom. 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.
Lift Cylinder Leakage Check
If internal leakage in one or both of the cylinders is
suspected, check for leakage as follows:
1. Remove the suspected cylinder from the machine. See
page 4-33.
2. Mount the cylinder in a suitable cylinder stand.
3. Connect a portable hydraulic system to the cylinder
base end.
4. Apply pressure to extend the cylinder rod.
5. Check the amount of leakage from the rod port of the
cylinder. If the cylinder leaks more than a few drops of oil
per minute, replacement of the piston seals is
necessary, See page 4-33.
WARNING
Do not adjust the holding valve setting. The valve is
adjusted by the manufacturer.
Reference Only