Single valve diaphragm pump with decreased sensitivity to ambient conditions

A positive displacement pump, comprising:

• a pump housing having an upper wall and a lower wall;
• a diaphragm operably attached to said housing and positioned between said upper wall and said lower wall, said diaphragm and said lower wall defining the boundary of said pump chamber, said diaphragm reciprocally movable from a rest position where said diaphragm contacts along the inner surface of said upper wall thereby conforming to the shape of said inner surface of said upper wall to an actuation position where said diaphragm contacts along the inner surface of said lower wall thereby conforming to the shape of said inner surface of said lower wall;
• an electromagnetic means for moving said diaphragm during an output stroke from said rest position wherein said pump chamber has a certain maximum volume to said actuation position wherein said pump chamber has a certain minimum volume;
• a spring means for returning said diaphragm during an intake stroke to said rest position, said output stroke being rapid compared to said intake stroke;
• a passageway providing bidirectional fluid communication between said pump chamber and a source of liquid to be pumped;
• an outlet valve and conduit in fluid communication with said pump chamber;
• and,
• an inlet filter means having a flow resistance characteristic which is identical for both inflow and outflow and is positioned in said passageway for permitting filling of said pump chamber at a first, comparatively slow rate during said intake stroke and cooperates with said variable volume means for generating sufficient fluid pressure in said pump chamber during a second, comparatively rapid output stroke to open said outlet valve and eject a substantial volume of liquid from said pump chamber.