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COMPONENTS CX130
CASE TRAINING CENTER
AUGUST 2000
Boom savety valve (H.B.C.V)
Purpose:
Two safety valves are fitted on the piston end of the boom cylinders. They avoid any uncontrollable boom down
movement when a plumbing failure may occur on the piping between the piston end cylinder and the control
valve.
Description:
3A Piloted check valve
3B Check valve
3C Spool
46G Relief valve including an anti-cavitation valve
The two piston ends are connected together by a hose to balance the pressure of the two cylinders. The
connecting ports of the balance hose get a restrictor.
A pressure sensor is fitted on P2 orifice to inform the controller of the piston end pressure.
Current operation
Neutral
The cylinder piston end is closed by 3B and 3A check valves. The check valve 3A cannot be pushed back
because its spring side is not connected with the tank by 3C spool.
Boom up
The remote control pressure (4b22) pushes the control valve spool. The oil flows out of the control valve (4B2
port), enters the safety valve (P1 port), pushes the (3B) check valve and goes out through the P2 directly
connected with the cylinder rod end. The oil of the rod end goes to the return through the (4A2) port of the control
valve.
Boom down
The pilot pressure 4a2 pushes the control valve spool and the safety valve spool (3C).
The oil flow supplies the cylinder rod end.
The spring side of the piloted check valve 3A is connected to the tank T1 by the cross drilled and centred drilled
holes of the spool 3C. It's pushed back and the oil from the cylinder rod end goes to the tank through the groove
of the spool 3C and the port 3B of the control valve.
Safety operation
If a pipe is broken between the piston end and the control valve the operator can operate the boom down. The
movement will be controlled by the metering notches of the spool 3C groove.
Leak specification
P2 to P1+ T1 < 4cc / mn at 9,81Mpa with oil temperature at 50°C
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