Abstract: A fluid pressure containment device utilizing a new design of pressure seal which accomplishes its purpose by a rotary motion of a tube placed inside a vessel. A helical slot cut into the tube causes the tube to rotate by the camming action of a free floating piston placed within the tube. The stationary outer vessel contains openings at its ends through which the working fluid medium may enter and exit and in addition is slotted, longitudinally for an attachment to the free floating piston to pass through the wall of the vessel as fluid pressure moves the piston longitudinally along the slot in the outer vessel. Sealing of the fluid pressure inside the stationary outer vessel is accomplished by the inside tube as it rotates and by a variety of seals which also serve as structural supports against pressure caused forces inside the tube.