| 摘要 |
A piston pump in which the piston carries a valve and a control mechanism to change a characteristic of the valve, preferably, its tendency to open. The valve may preferably comprise a disc which extends radially outwardly from the piston to resiliently engage the wall of piston chamber. The control mechanism preferably provides an access port communicating axially through the piston and axially out an opening of the piston chamber. In a preferred embodiment, the control mechanism comprises a bladder with a flexible side wall which can be moved from an inherent uncollapsed position to a different position and which bladder is inherently biased to return to its uncollapsed position. |
