Hydraulic systems

摘要

An hydraulic lift system has an actuator 2 connected to an hydraulic circuit, having a pump 31, via a supply line 20. A balanced seated valve 50 is connected between the supply line 20 and a reservoir 33, the valve being controlled by a solenoid 51 and an electric drive unit 40. The drive unit 40 supplies a gradually increasing or decreasing voltage to the solenoid 51 to open or close the valve 50 gradually. The valve has a valve member 170 that is displaceable along its length and has a valve head 174 of frusto-conical shape. A passage 176 along the valve member 170 balances fluid pressure across the valve member. The solenoid 51 has an armature 160 with a pole face 161 that can be displaced towards a fixed pole face 167 to unseat the valve member 170. The pole faces 161 and 167 have complementary frusto-conical surfaces 163 and there is a non-magnetic washer 168 between them. <IMAGE>