Hydraulic variable pumps and variable motors can adjust the output characteristics within a certain range according to the needs of the work under the action of the variable control device, and this feature has been widely used in many hydraulic equipments, such as: constant flow control, constant pressure control, constant speed control, constant torque control, constant power control, power matching control and so on. 

 Oil return process The plunger supplies oil upward, and when it goes upward to the slanting groove on the plunger (stopping the supply side) and the oil return hole on the sleeve, the low-pressure oil circuit of the pump room communicates with the center hole and radial hole and slanting groove on the head of the plunger, and the oil pressure drops suddenly, and the oil outlet valve closes quickly under the action of the spring force to stop supplying oil. Thereafter, the plunger will have to go up, when the cam cam part of the turn over, under the action of the spring, the plunger and go down. At this point the next cycle begins. 

 Axial piston pump is more than one plunger configuration in a common cylinder circumference, and make the plunger center line and cylinder center line parallel to a pump. Axial piston pump has two forms, straight shaft (swash plate) and oblique shaft (pendulum cylinder), the main body of this pump by the cylinder 1, with oil plate 2, plunger 3 and swash plate 4.