Pump with expandable chamber

A pump for pumping a liquid comprising:

• a housing having an inlet and an outlet, said housing including first and second housing sections and means for joining said first and second housing sections together;
• a flexible diaphragm sandwiched between said first and second housing sections;
• a pumping chamber in said housing;
• said housing having an inlet passage leading from said inlet to the pumping chamber and an outlet passage leading from said pumping chamber to the outlet;
• a positive displacement pumping member including a first portion of said diaphragm mounted for movement in said pumping chamber to pump the fluid from the inlet to the outlet;
• inlet check valve means for allowing liquid to flow through the inlet passage to the pumping chamber and for substantially preventing liquid flow in the reverse direction through the inlet check valve means;
• outlet check valve means for permitting liquid to flow from the pumping chamber through the outlet passage to the outlet and for substantially preventing liquid flow in the reverse direction through the outlet check valve means;
• means defining a resiliently expandable chamber opening into the inlet passage upstream of the inlet check valve means to receive the liquid and to be resiliently expanded thereby;
• and
• a second portion of said diaphragm sealing the interface between said housing sections, said housing having a cavity therein, a third portion of said diaphragm extending across said cavity to divide said cavity into at least said expandable chamber and a sealed chamber, said sealed chamber having a compressible gas therein whereby the third portion of the diaphragm can be deformed against the compressible gas in the sealed chamber to permit the resilient expansion of the expandable chamber.