GB1096610A - Fluid flow control valves - Google Patents

Abstract

1,096,610. Valves. NEW YORK AIR BRAKE CO. July 7, 1966 [Aug. 26, 1965], No. 30564/66. Heading F2V. A spool valve controlling the operation of a double-acting piston is provided with auxiliary valves which by-pass liquid from one side of the piston to the other to prevent cavitation when the piston is moved by its load at a speed greater than that with which the supply pump can keep pace. The auxiliary valves may be contained in the spool valve housing (Figs. 1-4, not shown), or they may be mounted externally of the latter as shown in Fig. 5. In the latter, the housing 111 has an inlet 112, exhaust 113, carry-over port 114 and two sets of motor ports (not shown) controlled by respective spool valves 127, 127b. During normal operation, the pump discharge pressure acts via line 173 on a piston 168 to cause the latter to urge a throttling spool 142 to the left. In this position, spool 142 provides a relatively unrestricted passage 149 for liquid returning via exhaust line 113a to tank 77. A rightward bias on the spool 142 is provided by liquid in chamber 155, this chamber communicating via orifice 157 with the exhaust line 113a upstream of passage 149. A relief valve 161 maintains the pressure in chamber 155 constant. If the controlled piston should move at an uncontrolled rate, the supply pressure in lines 112a and 173 will fall and the spool 142 will move to the right to throttle the exhaust line. When the backpressure in the latter reaches a predetermined value, check valve 137 (Fig. 2) opens to by-pass liquid to line 173 to supplement the supply from the pump 75. In the modification of Fig. 6, not shown, the relief valve 161 and orifice 157 are omitted and the constant rightward bias on the spool 142 is achieved with a low-rate spring.