| 摘要 |
<p>A two way closed-centre solenoid valve apparatus comprising a housing (32) defining a flow path interconnecting an inlet port (16), an outlet port (50) and a vent port (72) and a valve (14) in the flow path. In a first position, the valve (14) closes communication from the inlet port (16) to both the outlet port (5) and the vent port (72); in a second position the valve opens communication between the inlet port (16) and only the outlet port (50), and in a third position it opens communication between the outlet port (5) and only the vent port (72). The valve (14) defines a predetermined sealing area upon which fluid pressure is effective to urge the valve from the fluid position towards one of the second and third positions. The apparatus includes input means (80-92) for selectively moving the valve from the first position alternatively to either one of the second and third positions. The apparatus also includes feedback means having a first feedback area (128) significantly exceeding the predetermined sealing area and arranged to urge movement of the valve means from either the second or the third position towards the first position in response to fluid pressure effective thereon, and means (124) communicating fluid pressure from the outlet port to the first feedback area (128) as a first time derivative of the fluid pressure level at the outlet port to act upon the first feedback area.</p> |
