A pump comprising a piston in communication with a valve chamber provided with a first valve seat and a second valve seat, and a resilient valve element comprising a first tapered portion, a second tapered portion and a flange portion extending from a periphery of the first tapered portion, in which the flange portion co-operates with the first valve seat to form an inlet valve, and the second tapered portion co-operates with the second valve seat to form an outlet valve, and in which negative pressure applied to the flange portion by the pressure means in use lifts it from the first valve seat, and positive pressure applied to the first tapered portion by the piston in use lifts the second tapered portion from the second valve seat.