a pump for pumping an incompressible liquid comprising a housing having an inlet and an outlet , a pumping chamber in said housing , and a positive displacement pumping member mounted for movement in the pumping chamber . the housing has an inlet passage which leads from the inlet to the pumping chamber and an outlet passage leading from the pumping chamber to the outlet . inlet and outlet check valves are provided in the inlet and outlet passages , respectively . a resiliently expandable chamber opens into the inlet passage upstream of the inlet check valve to receive the liquid and to be resiliently expanded by it .