A pump comprising a housing including first and second housing sections and a gasket between the first and second housing sections. The housing has a first pumping chamber, an inlet, an inlet passage in the housing leading from the inlet to the pumping chamber, an outlet and an outlet passage in the housing leading from the pumping chamber to the outlet. A pumping member is movable in the pumping chamber to pump fluid through the pump. Inlet and outlet check valves are provided in the inlet and outlet passages, respectively with each of the check valves including a movable valve element. The gasket forms a seal between the first and second housing sections. A bypass passages (140) in the housing leads from a location in the outlet passage downstream of the outlet check valve to a location in the inlet passage upstream of the inlet check valve. A bypass valve is provided and includes a bypass valve seat in the bypass passages, a region of the gasket and a biasing member for biasing the gasket region against the bypass valve seat to close the bypass passage.