Load dependent hydraulic drive for lift - has slide and throttling valve operated by electric motor to prevent system oscillations

摘要

The hydraulic lift drive has a constant delivery rate pump which loads a hydraulic cylinder through a control valve. A throttling slide valve is fitted in parallel with the pump. The drive prevents the generation of regulating circuit oscillations. The throttling slider is operated by a reversible electric servomotor in relation to the travelling direction, speed and location of the lift. It can be stopped or driven in either rotating direction at constant speed. The valve between the constant delivery rate pump and hydraulic cylinder has three valve faces loaded by the pressures of the pump, hydraulic cylinder and valve outlet pressure.