VENTIL FOR HYDRAULSYSTEM MED ANSLUTNING FOR EN HUVUDPUMP OCH EN RESERVPUMP

摘要

A valve device having a pressure operable valve piston, particularly for booster steering systems, to selectively control pressure flow to a consumer device such as a hydraulic servomotor in order to permit use of a reserve pump in event of failure of a main pump. The valve in a neutral position blocks the output of both pumps to a sump but is responsive to a first increase in flow rate beyond a predetermined limit to shunt flow from the reserve pump to a sump. Upon further increase in flow rate the valve piston moves to a position to also shunt part of the output from the main pump to a sump. Differential pressure acting on a valve piston effects shifting and means are provided to vary the differential pressure required to shift the valve piston so that a greater differential pressure is needed for the shifting of the valve piston for the partial shunting of the main pump output. Signal means is actuated by movement of the valve piston to apprise a vehicle driver that the valve device is operative.