Patent ID: 6991215

Claim:
A valve assembly that comprises an inlet and an outlet, a flow pathway that extends through the valve assembly from the inlet to the outlet, a plunger that is positioned in the flow pathway and which can move between a forward open position where fluid can flow from the inlet to the outlet, and a retracted closed position where fluid is prevented from flowing from the inlet to the outlet, the plunger having a fluid flow pathway extending at least partially therethrough or therealong, the plunger having a forward portion, an at least partially elastic sock that has an outer end fixed to the valve assembly, and an inner portion which engages with the plunger such that reciprocation of the plunger from the retracted position to the forward position causes at least part of the sock to stretch, and a variable volume chamber having walls defined by the plunger and the sock, the chamber forming part of the flow pathway, the chamber having smaller or nil volume when the plunger is in the retracted position, and a larger volume when the plunger is in the extended position, whereby upon retraction of the plunger, the variable volume chamber reduces in volume which results in a pumping action to pump fluid through the fluid pathway towards the outlet, thereby reducing or preventing backflow.