DIAPHRAGM PUMP

Diaphragm pump (110) for receiving drive power from a motor, said pump comprising: a housing (112, 137) having a pumping chamber (106) adapted to contain fluid to be pumped, a transfer chamber (44) adapted to contain hydraulic fluid, and a hydraulic fluid reservoir; a diaphragm (34) having a transfer chamber side and a pumping chamber side, said diaphragm (34) being disposed between said pumping chamber (106) and said transfer chamber (44) and adapted for reciprocation toward and away from said pumping chamber (106); a piston (46) in a cylinder (120) in said housing (112, 137) adapted for reciprocation between a power stroke and a suction stroke, said cylinder (120) forming a portion of said transfer chamber (44), said piston (46) moving longitudinally in said cylinder (120) with said cylinder (120) having a surface with an upper portion (118) when said pump (110) is oriented so that said cylinder (120) is generally horizontal; a fluid communication path for the hydraulic fluid between said hydraulic fluid reservoir and said transfer chamber (44) and a valve in said path for selectively allowing flow of hydraulic fluid from said hydraulic fluid reservoir to said transfer chamber (44) when said valve is open.