| 摘要 |
A piston mechanism for sensing a control fluid pressure and shifting a valve element in response thereto. The piston mechanism comprises a first piston having an internal bore in which is positioned a second piston. Varying ranges of fluid pressure sufficient to actuate the piston mechanism are accomplished by positioning the piston mechanism within its piston chamber in varying orientations so that the effective piston surface area exposed to a control fluid is dictated by the specific orientation of the piston mechanism within the chamber. In one orientation, the effective fluid pressure surface area is that of the larger piston member. In a second orientation, the effective surface area exposed to the sensing fluid is a first surface of the smaller piston carried by the larger piston. In a third orientation, the effective surface area exposed to the sensing fluid is that of the opposite end of the second piston. To effect these various orientations of the piston mechanism, the piston orientation is reversed and O-rings relocated about the pistons, and in one orientation, a spacer is provided to cause the two pistons to shift simultaneously. In this manner, varying ranges of sensing fluid pressure sufficient to shift a pilot valve or other valve is accomplished with the use of a single spring within the valve to urge the valve element into position against the action of the sensing fluid pressure force.
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