Engine drives the oil pump so that high pressure oil can enter into the P cavity of valve block and come out of the A cavity through the No.1 non-return valve and enter into the elevating oil cylinder so that operating platform can rise slowly. Working pressure can be adjusted by the No. 2 overflow valve according to different loads to avoid overload or excessive pressure. Power on to open the No.4 electromagnetic valve when working platform declines and hydraulic oil of elevating oil cylinder flows into the valve block through A cavity under load gravity of working platform. The No. 1 non-return valve only can be closed reversely so hydraulic oil only can be drained into the oil tank from O cavity through adjustable throttling valve so that working platform can decline slowly. (As shown in Figure), pressure balance structure has been adopted in the valve and it only can be controlled by electromagnet to open or close so stability of elevation and subsidence speed will not be influenced by load fluctuation.
