Fluid pressure powered apparatus

A method comprising:

• reciprocating a double-acting member using fluid pressure;
• controlling the reciprocation of the double-acting member using a switch having at least two positions;
• and
• controlling the switch by establishing biasing fluid pressures to a first bias surface and a second bias surface of the switch to maintain the switch in position, and selectively and temporarily reducing a corresponding one of the biasing fluid pressures to cause the switch to switch positions.

A fluid pressure powered pump comprising:

• a fluid pressure valve having a first surface and a second surface, the fluid pressure valve switchable between a first position and a second position;
• a double-acting member operable by fluid pressure from the fluid pressure valve:
• through a first stroke towards a first end in the first position;
• and
• through a second stroke towards a second end in the second position;
• and
• a first pilot valve and a second pilot valve configured in operation to establish biasing fluid pressures to the first surface and the second surface, respectively, during both the first stroke and the second stroke, the first pilot valve and the second pilot valve being actuatable by the double-acting member at or near the first end and the second end, respectively, to reduce the biasing fluid pressure on the first surface and the second surface, respectively, to switch fluid fluid pressure valve positions.

A method of driving a fluid pressure powered apparatus having a double-acting member operated by fluid pressure from a switchable valve, the method comprising:

• supplying biasing fluid pressures to a first bias surface and a second bias surface of the switchable valve to maintain the switchable valve in a first position;
• establishing a first fluid pressure differential across the double acting member towards a first stroke end to move the double-acting member towards the first stroke end;
• reducing the biasing fluid pressure on the second bias surface when the double-acting member reaches the first stroke end to cause the switchable valve to shift to a second position;
• supplying biasing fluid pressures to the first bias surface and the second bias surface to maintain the switchable valve in the second position;
• establishing a second fluid pressure differential across the double acting member towards a second stroke end to move the double-acting member towards the second stroke end;
• and
• reducing the biasing fluid pressure on the first bias surface when the double-acting member reaches the second stroke end to cause the switchable valve to shift to the first position.