Controlled release door holder

Abstract

A controlled release door holder comprises a housing having a portion defining a cylinder for containment of a fluid, a piston received in the cylinder for movement axially thereof and dividing the cylinder into first and second chambers, and a linkage between the piston and the door for moving the piston in the cylinder as a function of door movement. A spring compressed between the piston and housing biases the door toward the closed position. Three hydraulic paths communicate the sections of the cylinder on either side of the piston: the first path includes a check valve that allows one-way flow from the spring side to the other side as the door is opened; a second path, which includes a pressure relief valve, allows flow from the other side to the spring side when the door is pushed closed, but resists the spring pressure and holds the door in any desired position; a controllable valve responds to control signals to shunt the fluid pressure generated by the spring in the other side of the cylinder to the spring side so that the spring force acting on the piston moves the door, by force transmission through the linkage, toward closed position.