Patent ID: 7647942

Claim:
A valve for maintaining a substantially constant fluid flow rate in response to varying pressure across said valve, said valve comprising: a housing having an inlet duct and an outlet duct; a sleeve rotatably positioned within said housing; an inlet aperture and an outlet aperture extending through said sleeve, rotation of said sleeve aligning at least a portion of said inlet and outlet apertures with said in let and outlet ducts respectively, said fluid flow rate being proportional to a first area of overlap of at least one of said inlet and outlet apertures with one of said inlet and outlet ducts; a piston slidably positioned within said sleeve, said piston having first and second ends oppositely disposed; a conduit providing fluid communication between said first and second ends of said piston, said conduit controlling sensitivity of response of said piston to pressure changes between said inlet and outlet ducts; and an inlet opening and an outlet opening extending through said piston, sliding motion of said piston aligning at least a portion of said piston's inlet and outlet openings with said sleeve's inlet and outlet apertures respectively, said flow rate being further proportional to a second area of overlap of at least one of said inlet and outlet openings of said piston with one of said inlet and outlet apertures of said sleeve, said piston being movable in response to said pressure to vary said second area of overlap to maintain said fluid flow rate substantially constant.