Abstract: A pressure relief valve has a moveable piston disposed in a body between inlet and outlet ports in the body. A volumetrically variable enclosed chamber is formed within the body with a portion of the chamber being defined by an upper surface of the piston. At least one aperture extends through the head of the piston providing a fluid passageway between an inlet port of the valve and the enclosed chamber. Fluid captured within the enclosed chamber permits initial rapid movement of the piston head to an open, or relieved, position in the event of a sharp increase in system pressure and provides a hydraulic cushion whereby impact shock of the head against internal valve components is attenuated.

Abstract: A semiactive heave compensation system for marine vessels, especially floating offshore drilling rigs, is described. The system can be installed in its entirety or can be used to modify existing passive systems by including heave and compensating sensors a microprocessor and a responsive operator to act upon the compensation elements of the system.

Abstract: A hydropneumatic cable tensioner is comprised of an enclosed cylinder featuring a plurality of annular chambers. A fixed cable sheave is mounted to one end of the cylinder. A movable cable sheave is mounted to a piston rod connected to a piston which reciprocates in the innermost or piston bore chamber of the cylinder. Regulated compressed gas is connected to the outer chamber of the cylinder thereby exerting high pressure forces on oil found in the middle or high pressure oil chamber of the cylinder. Pressurized oil forces a piston to move outwardly thereby increasing the distance between the two sheaves and tensioning a cable. Restriction means within the piston bore chamber regulate movement of the piston and prevent uncontrolled acceleration should a cable failure occur.