| 摘要 |
A hydraulic valve includes a spool movable from an inactive position to a pair of operating positions in each of which one of a pair of motor ports is pressurized. A detent latches the spool in its operating positions, and a spring biased plunger normally urges the detent into engagement with the spool. One side of the plunger is exposed to valve inlet pressure, and normally the plunger is maintained in hydraulic balance by means of restricted communication between its two sides. A pair of pressure responsive valves communicate between the second side of the plunger and the motor ports, and are independently adjustable to open at predetermined pressures thereby to unbalance the plunger and release the spool from the operating positions. The valve may be provided with a centering spring so that upon release the spool returns to its inactive position. Alternatively, the valve is provided with a reversing spring arrangement serving to reverse the operation of the valve when the spool is released from a first operating position so that a pair of operations are automatically carried out in sequence. A system including two or more valves carries out several hydraulic operations in sequence.
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