Valve mechanism for a hydraulic expansible chamber motor

Abstract

A hydraulic valve mechanism for a hydraulic motor having a cylinder and a piston reciprocating therein, comprising a valve block having a valve face, a main and an auxiliary central exhaust ports, two main feed ports on opposite sides of the main exhaust port, and two auxiliary feed ports on opposite sides of the auxiliary exhaust port. A valve chest is sealed over the valve face and has aligned piston-receiving bores at its opposite ends, a chamber for pressurized hydraulic fluid between the bores and a valve-actuating piston slideable in the bores. A main D-valve and an auxiliary D-valve operable by the valve-actuating piston move within the chamber in sliding sealing engagement with the valve face. The main D-valve covers and uncovers the main exhaust port and main feed ports to control the reciprocation of the motor piston. The auxiliary D-valve covers and uncovers the auxiliary exhaust port and auxiliary feed ports which communicate with closed ends of the bores to control the position of the valve-actuating piston and the main D-valve. The auxiliary D-valve is so formed in relation to the auxiliary feed ports that it does not completely block hydraulic fluid flow through either one of the auxiliary feed ports at any position along its line of motion, thereby preventing hydraulic lock.