Patent ID: 7325660

Claim:
An apparatus useful to regulate fluid flow, comprising a valve housing having a passage for fluid flow through the valve housing, a piston configured to move in response to application of fluid forces toward and away from a position that closes the passage; a flow regulating mechanism including a regulator arranged to regulate flow of fluid through the passage, the flow regulating mechanism including a plurality of selectable settings that are accessible from outside the valve housing and including a regulator movable to vary a dimension of at least a portion of the passage in accordance with a selected one of the selectable settings so as to provide a substantially linear variation in the flow of fluid through the passage as the regulator moves to a position corresponding to the selected one of the selectable settings, the flow regulating mechanism providing regulation of the flow of fluid through the passage substantially independent of movement of the piston as the piston remains clear of closing the passage; and the valve housing is cylindrical and includes an opening configured to be indicative of a triangular shape the regulator being configured to be indicative of a rectangular shape configured to partially close the opening during relative movement of the regulator within the valve body.