Patent ID: 7527070

Claim:
A method for controlling fluid flow through a passageway, comprising: slidably disposing a piston in the passageway, the piston having a conduit that reduces the flow area through the passageway; selectively closing the conduit of the piston using a plug having one or more annular seals, the selective closing being achieved by movement of the piston to a stop position where the plug sealingly engages a portion of the piston conduit, wherein the plug is biased to a first position when the piston conduit is moved to the stop position, and wherein the plug is moveable to a second position that opens the piston conduit under fluid pressure in the passageway that overcomes the bias; and pumping fluid though the passageway using a two-stroke piston pump when the piston conduit is opened; wherein selectively closing the piston conduit and pumping fluid through the passageway is configured such that fluid is not pumped through the passageway when the piston conduit is closed, including by: closing the piston conduit at or near the time that the pump completes one stroke of its two-stroke cycle; and opening the piston conduit at or near the time that the pump completes the other stroke of its two-stroke cycle.