Patent ID: 6901911
Filing Date: 2005-06-07
Classification: F04B

Abstract:
1. A liquid pump comprising: a pump body having disposed therein an outlet area, at least one pumping chamber and an inlet area; a check valve separating the outlet area from the at least one pumping chamber; at least one pump piston moveably positioned in said pump body; and an electro-hydraulic controller attached to said pump body and being moveable between a first position at which said pump piston displaces fluid in a large proportion to said outlet area relative to said inlet area, and a second position at which said pump piston displaces fluid in a small proportion to said outlet area relative to said inlet area, and including a mechanical biaser operable to bias said electro-hydraulic controller toward said first position, and including a biasing hydraulic surface oriented in opposition to said mechanical biaser for hydraulic biasing toward said second position, and including a control hydraulic surface oriented in opposition to said biasing hydraulic surface; said control hydraulic surface is exposed to fluid pressure in a control volume fluidly connected to said outlet area; said biasing hydraulic surface is exposed to fluid pressure in a biasing volume fluidly connected to said outlet area; and said control volume and said biasing volume are fluidly connected to said outlet area via a pressure reduction valve that is located downstream from the check valve.