Patent ID: 8091857

Claim:
A valve assembly to control flow of a fluid under pressure including: a body having a bore with a longitudinal axis and surrounding a chamber, a first and a second opening in the body providing for fluid flow via the openings through the chamber; a movable valve chamber located in the chamber and movable longitudinally thereof between a first position and a second position, said movable valve member having a transverse passage that is aligned with the openings when the valve member is in the first position to thereby provide for said fluid flow, and displaced relative to said openings to said second position to prevent fluid flow between the openings when this valve member is in the second position; a first piston and a second piston, each of the pistons being attached to the valve member so the valve member is located longitudinally between the pistons, the pistons being operatively associated with the bore and valve member so as to define a first sub-chamber and a second sub-chamber being located between the second piston and the valve member, the first piston also being operatively associated with the bore to provide a third sub-chamber by the first piston, the second piston being operatively associated with the bore to provide a fourth sub-chamber, the second piston being located so as to be positioned between the second sub-chamber and the fourth sub-chamber; a first port, the first port being operatively associated with the third sub-chamber to provide for the flow of fluid with respect thereto; a second port, the second port being operatively associated with the fourth sub-chamber to provide for the flow of fluid with respect thereto; a valve member guide, said guide providing a pair of generally parallel longitudinally extending guide surfaces, with said valve member being slidably engaged with the guide surfaces so that the movable valve member is located between the guide surfaces, the guide including a pair of guide plates providing said guide surfaces between which the valve member is located so as to be guided thereby, each guide plate having a guide fluid flow passage aligned with a respective one of the first and second openings; and wherein said first sub-chamber and second sub-chamber are in fluid communication, with said movable valve member being moved between the first and second positions thereof by fluid under pressure being delivered to the third sub-chamber or the fourth sub-chamber depending on the direction in which the movable valve member is to be moved.