Patent ID: 8156960

Claim:
A valve for controlling pressure in a system comprising: a housing; a servo spool positioned within the housing, the servo spool having at least a first fluid passage and a second fluid passage therein; a piston positioned within the housing and at least partially surrounding the servo spool, the piston and the servo spool being movable relative to each other, the piston defining a first orifice configured to communicate with a supply of pressurized fluid and a second orifice configured to communicate with a portion of the system; a first chamber at least partially defined by the housing and the piston, the first chamber being arranged such that force due to fluid pressure in the first chamber is configured to move the piston in a first direction, the first chamber including a third orifice configured to communicate with a controlled pressure in the system; a second chamber at least partially defined by the housing and the piston and including a fourth orifice configured to communicate with a low pressure fluid source; and a biasing element arranged in the second chamber, the second chamber and the biasing element being arranged such that a force produced by the biasing element is configured to move the piston in a second direction; wherein the first and second fluid passages in the servo spool are configured such that in at least one relative position of the piston and the servo spool the first fluid passage provides communication between the first orifice and the second orifice and in at least one other relative position the second fluid passage provides communication between the second orifice and the fourth orifice.