Fluid driven reciprocating pump

A fluid driven reciprocating pump, comprising:

• a pair of heads each containing a displaceable member defining a drive chamber and a pump on opposite sides of the displaceable member in one head, and a drive chamber and an inactive chamber on opposite sides of the displaceable member in the other head;
• a first mechanical coupling connecting the two displaceable members for reciprocation together;
• a control valve assembly connecting the drive chambers of both heads to a source of pressurized fluid for driving them through forward strokes;
• a spring for driving said heads through return strokes;
• and means connecting the pump chamber of said one head to a source of material to be pumped;
• said control valve assembly comprising:
• a housing having a displaceable diaphragm defining a pressure chamber and a control chamber on opposite sides thereof;
• an inlet port leading to said pressure chamber for connecting it to said source of pressurized fluid;
• a drain port leading to said control chamber for draining said control chamber;
• outlet port means leading from said pressure chamber for connecting it to the drive chambers of the two heads;
• a main valve coupled to said diaphragm of the control valve assembly so as to be movable thereby either to an open position establishing communication between said pressure chamber and said outlet port means to drive said pump through its forward strokes, or to a drain position interrupting said communication and thereby to permit said spring to drive the pump through its return strokes;
• a pilot valve member within said housing and comprising a stem passing through said diapragm;
• a second mechanical coupling connecting said pilot valve member stem to said first mechanical coupling so as to be moved thereby at the end of the pump forward strokes to establish communication between said control chamber and said drain port to drain said control chamber, and at the end of the return strokes to interrupt said communication and thereby to permit the control chamber to rise to the pressure of the pressure chamber to move the main valve member to its open position and to cause the pressurized water to drive the pump through its forward strokes;
• and a further drain port within said housing;
• said main valve being a piston movable within the housing from an open position connecting said outlet port means to said pressurized chamber of the control valve assembly, or to a closed position connecting said outlet port means to said further drain port of the control valve assembly.