Volvo EC330B Excavator Rebound damping valve operation

Procedures:
(1) Neutral position
(2) Start of swing
(3) full swing
(4) Joystick return to the neutral. PA pressure goes high.
(5) PA will reach to relief valve set pressure and machine will stop.

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In this point, PA=Relief set pressure and PB=Tank pressure.There is pressure difference between PA & PB. That means rebound of machine.
(6) When machine starts rebound, PA pressure drops down.
If PA is lower than the spring force of damping valve, those two valves starts to return to original position.
But return speed is different because of small hole of front valve. This speed difference make gap between two valves. This gap connects A & B ports. As result, PA & PB will be same for short time. That means there is no force to rotate motor again.
Finally, this valve can stop the machine at the early stage of first rebounding.
During normal slewing, the port A & B must be disconnected at any case.

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