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| Illustration 1 | g00524562 |
When the cylinder is retracted, pressure oil flows through the port of the check valve into the passage. The oil pushes on the load on the back of the check valve cone and the poppet. This lifts the check valve cone and the poppet out of the valve seat. The pressure oil can go to the rod end and the cylinder retracts.
When the cylinder movement is stopped, the check valve cone and the poppet are closed again. The load is held by the sealed check valve. Any pressure spikes are relieved over the relief valve that is installed in the bypass.
When the cylinder is being extended, control pressure from the left hand pilot control valve goes to the pilot oil port of the check valve. The pilot oil moves the pilot piston and the poppet is opened. The load pressure that is applied through the passage goes to the head area of the equalizing spool and through the passages. The load pressure also goes to the surface of poppet.
The diameter of the cylindrical control section of the poppet corresponds to the diameter of the equalizing piston. The valve is in a state of equilibrium in this condition.
At the same time, pilot oil goes through the passage to the unlocking piston. As the pressure increases, this piston is pushed against the force of the spring so that a controlled opening is formed at the poppet. Pressure oil can flow from the rod end port to the head end port and to the main control valve port. The cylinder now extends.
If cylinder movement is interrupted, the spring returns the pilot piston to the normal position. As a result, the force of spring also pushes the poppet back into the seat. The load pressure to equalizing piston is now interrupted.
The unlocking piston which was previously pushed back by the force of the spring, and equalizing piston are returned to the normal position.
Load pressure at the equalizing piston is reduced via leakage at the shaft of the poppet into spring chamber of the unlocking piston.