Straight shaft and inclined plate type piston pump is divided into two kinds of pressure oil supply type and self absorption type. Pressure supply type hydraulic pump is mostly used in the oil tank, the hydraulic oil tank by the pressure, after each start of the machine, must wait for the hydraulic tank to reach the use of air pressure, to operate machinery. Such as tank of the hydraulic pressure is insufficient will start the machine, the hydraulic pump and slipper caused by pull off phenomenon, can cause abnormal wear of the pump body return plate and the plate.