The present invention provides a one way valve having a valve body, a wall, a fluid inlet, and a fluid outlet. The valve has a plunger which is moveable with respect to the valve body from a first position to a second position. The valve also has a diaphragm positioned in the valve body for movement between a third position and a fourth position when the plunger is in the first position. When the diaphragm is in the third position the fluid outlet is closed and when the diaphragm is in the fourth position the fluid outlet is open.