CONTINUOUSLY SELF-COMPENSATING HYDRAULIC POSITIONER

摘要

A hydraulic positioner has a cylinder. There is a piston chamber in the cylinder closed at one end by an axially displaceable gland. A piston is reciprocable in the chamber. There is a rod connected to the piston and slidable through the gland. The rod is moveable with the piston between an extended and a compressed position. The piston chamber contains hydraulic fluid and there are valve means in the piston actuatable to allow flow of the fluid across the piston. The valve is normally closed for locking the piston and the rod against movement in the cylinder. A spring urges the rod to the extended condition. A further spring urges the gland against the fluid to compensate the changes in fluid volume in the chamber. The positioner is able to compensate for thermal expansion and contraction of the hydraulic fluid without the necessity to move the cylinder to a particular position after use. The cylinder of the positioner is also able to compensate for the change in effective piston chamber volume which occurs as the piston rod moves in and out of the chamber during the stroke of the piston.