Hydraulic reciprocating mechanism

An reciprocating mechanism which is powered by pressurized water and which comprising:

• a housing;
• a piston located reciprocably in the housing and defining, with the housing, a supply chamber and a return chamber, the return chamber having respective first and second ends and the piston presenting exposed, differential piston areas on which forces generated by the water act, during operation of the mechanism, to cause reciprocation of the piston;
• an inlet to the supply chamber for pressurized water;
• an exhaust outlet from the return chamber;
• an interconnecting passage extending between the supply chamber and the return chamber;
• and
• a single poppet valve which is located reciprocably in the return chamber for movement, under the influence of force of pressurized water, between:
• a first position in which the poppet valve seats against the first end of the return chamber so as to close the exhaust outlet and open the interconnecting passage to admit water from the supply chamber to the return chamber with the result that the water in the return chamber drives the piston in a first direction;
• and
• a second position in which the poppet valve seats against the second end of the return chamber so as to close the interconnected passage and open the exhaust outlet to allow water to be exhausted from the return chamber by the piston as the piston is driven a second direction, opposite to the first direction, by water in the supply chamber,
• wherein:
• the arrangement is such that the poppet valve is moved, by force of pressurized water acting on it, from its first position to its second position as the piston approaches the end of a stroke in the first direction and from its second position to its first position as the piston approaches the and of a stroke in the second direction,
• the poppet valve is annular in shape, with inner and outer surfaces, and surrounds the piston, the outer surface of the poppet valve being exposed continuously to the pressure of water at the inlet and being shaped such that the poppet valve experiences a force, due to the pressure of water at the inlet tending to move it from its first position to its second position,
• the supply chamber includes a supply zone in direct communication with the inlet and an intermediate zone connected to the return chamber by the interconnecting passage,
• the housing defines an annular constriction between the supply and intermediate zones,
• a section of the piston is arranged to make a close fit with the annular constriction as the piston approaches the end of its stroke in the first direction, with the result that, with further movement of the piston in the first direction, there is a reduction in water pressure in the intermediate zone of the supply chamber and in the return chamber, such pressure reduction causing a pressure differential across the poppet valve which urges the poppet valve from its first position to its second position,
• the inner surface of the poppet valve defines an annular poppet valve constriction about the piston with respective portions of the return chamber being defined between the first end of the return chamber and the poppet valve constriction and between the second end of the return chamber and the poppet valve constriction, and
• a section of the piston makes a close fit in the poppet valve constriction when the piston approaches the end of its stroke in the second direction, with the result that water pressure increases in that portion of the return chamber defined between the second end thereof and the poppet valve constriction, such pressure increase urging the poppet valve to move from its second position to its first position.

A reciprocating mechanism which is powered by pressurized water and which comprises:

• housing;
• a piston located reciprocably in the housing and defining, with the housing, a supply chamber and a return chamber, the return chamber having respective first and second ends and the piston presenting exposed, differential piston areas on which forces generated by the pressurized water act, during operation of the mechanism, to cause reciprocation of the piston;
• an inlet which is connectable to a supply of pressurized water and which delivers the pressurized water to the supply chamber;
• an outlet for exhausting water from the return chamber;
• and
• an interconnecting passage extending between the supply chamber and the return chamber;
• a single poppet valve which is located reciprocably in the return chamber for movement, under the influence of forces generated by the pressurized water, between:
• a first position in which the poppet valve seats against the first end of the return chamber so as to close the exhaust outlet and open the interconnecting passage to admit pressurized water from the supply chamber to the return chamber with the result that the pressurized water in the return chamber drives the piston in a first direction, and
• a second position in which the poppet valve seats against the second end of the return chamber so as to close the interconnecting passage and open the exhaust outlet to allow water to be exhausted from the return chamber by the piston as the piston is driven a second direction, opposite to the first direction, by pressurized water in the supply chamber.