Fluid actuator with internal pressure relief valve

A fluid actuator of the type for producing reciprocal movement, said actuator comprising:

• a cylindrical housing adapted to be secured to a relatively stationary object, said housing having first and second end portions and respective first and second fluid ports positioned therein;
• a piston disposed for relative movement within said housing, said piston defining first and second fluid chambers within said housing, said first fluid chamber being in communication with said first fluid port and said second fluid chamber being in communication with said second fluid port;
• a piston rod connected to said piston and extending outwardly from said first end portion of said housing, said piston rod adapted to be connected to an object to be moved;
• a conduit communicating with said first fluid chamber through said first fluid port in said first end portion of said housing, said conduit extending longitudinally from said first fluid port alongside said housing to said second end portion of said housing;
• said second end portion of said housing having a passageway disposed therein and in fluid communication with said second fluid chamber through said second fluid port and in fluid communication with said first fluid port through said conduit;
• valve means disposed within said passageway of said second end portion of said housing and in fluid communication with said second fluid chamber through said second fluid port and in fluid communication with said first fluid port through said conduit for controlling the fluid pressure within said first and second chambers responsive to pressure in any one of said chambers exceeding a predetermined pressure therein and to moderate movement of said piston responsive thereto, said valve means comprising a pair valves disposed within said passageway and arranged in fluid communication with each other so that when one valve is urged in an open position the other valve is urged in a closed position, each of said valves comprising an adjustable valve seat, a ball member positioned on said valve seat, and a spring cooperating with said ball member for maintaining said ball members in cooperating relation with said valve seat;
• and
• pressure selective means cooperating with said adjustable valve seat of each of said pair of valves within said passageway for selectively adjusting the position of said valve seat which in turn adjusts the compressing force of said spring on said ball member and to thereby adjust said predetermined pressure.