| 摘要 |
<p>A pilot valve for a two-stage hydraulic device, the pilot valve comprising a spool slidably mounted in a housing for movement in opposite directions from a normal null position in order to deliver fluid under pressure from an inlet port through one or other of two service ports to a second stage of the device to actuate the latter in one direction or an opposite direction from a normal null position, and an electrically-actuated spool control device, associated with one end of the spool. The pilot valve spool is movable beyond its normal operating range to an offset zero flow position in the event of a failure of a control device. A spring is disposed at one end of the pilot valve spool and is operable, in the event of failure of a control device, to move the spool to a predetermined position. A stop for the spring prevents further movement of the spool beyond the predetermined position. The pilot valve is constructed to allow pressure fluid to react on the pilot valve spool so that when the spring engages the stop, this reaction results in movement of the spool to move the spool fully to the dump position in which both service ports are connected to tank, flow of fluid under pressure is metered from the inlet port through the service port, which would otherwise be subjected to such flow in such offset position of the pilot spool.</p> |
