| 摘要 |
A spool valve is formed from a spool having two adjacent lands of equal cross-sectional dimensions, and a third land having greater cross-sectional dimensions than the other two. The spool reciprocably moves through a bore formed in a housing, so as to open and close fluid communication between selected pairs of ports formed in the housing. The bore includes a first chamber which receives the third land of the spool and has no externally communicating port formed in its walls. The spool valve may be used as a control valve for the actuator of a system valve. As the spool valve begins to actuate, the third land becomes exposed to actuator pressure. The greater area of the third land serves to increase the force applied to the spool valve by the actuator pressure source, enhancing protection from unintended or malicious resetting of the spool.
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