Patent ID: 7735517

Claim:
A valve for controlling fluid flow in a fluid system, the valve comprising: a housing; a servo spool positioned at least partially within the housing, the servo spool including a substantially cylindrical portion, the substantially cylindrical portion defining a spiral groove extending around the substantially cylindrical portion to define a spiral land; a piston positioned at least partially within the housing and at least partially surrounding the substantially cylindrical portion of the servo spool, the piston defining an orifice configured to provide flow communication to a supply of pressurized fluid and an orifice configured to provide flow communication to a portion of the fluid system exterior to the valve; a main spool operably coupled to the piston, the main spool configured to control flow of fluid in the fluid system; a first chamber at least partially defined by at least one of the housing, the servo spool, and the piston; a second chamber at least partially defined by at least one of the housing, the servo spool, and the piston; wherein the first chamber is located such that force due to fluid pressure in the first chamber is configured to move the piston in a first direction, and the second chamber is located such that force due to fluid pressure in the second chamber is configured to move the piston in a second direction, and wherein the spiral groove and spiral land are configured such that angular displacement of the servo spool results in providing flow communication between the first chamber and the portion of the fluid system exterior to the valve via one of the orifices and between the supply of pressurized fluid and the second chamber via another of the orifices, such that fluid pressure in the first chamber is changed and fluid pressure in the second chamber is changed, resulting in a force imbalance on the piston, thereby moving the piston and the main spool in one of the first direction and the second direction.