Analysis of the working principle of Rexroth piston pumps – Autosys Hydraulics

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　Parker piston pumps are an important component in hydraulic systems. It relies on the reciprocating movement of the plunger within the cylinder body to change the volume of the sealed working chamber, thereby achieving oil suction and oil compression. Plunger pumps feature high rated pressure, compact structure, high efficiency, and easy flow regulation, and are widely used in applications that require high pressure, large flow rates, or flow regulation, such as hydraulic presses, construction machinery, and ships. 　　The total stroke L of the plunger’s reciprocating motion in a plunger pump remains constant and is determined by the lift of the cam. The amount of fuel supplied per cycle by the plunger depends on the fuel supply stroke, which is variable and not controlled by the camshaft. The start time of fuel supply does not change with variations in the fuel supply stroke. Rotating the plunger can change the timing of fuel supply, thereby altering the amount of fuel supplied. When a plunger pump is in operation, the cam on the fuel injection pump’s camshaft, together with the force exerted by the plunger spring, forces the plunger to move up and down reciprocally, thereby carrying out the task of pumping oil. The oil-pumping process can be divided into the following three stages. 　　Oil intake process: When the protruding part of the cam rotates past, the plunger moves downward under the force of the spring. A vacuum is created in the space above the plunger (referred to as the oil pumping chamber). Once the upper surface of the plunger opens the oil inlet hole in the plunger sleeve, the diesel fuel contained in the oil passages of the pump’s upper part enters the oil pumping chamber through this hole. When the plunger reaches its lower dead center, the oil intake process is complete. 　　Fuel supply process ； 　　When the camshaft rotates and the protruding part of the cam lifts the roller body, the plunger spring is compressed, the plunger moves upward, the fuel is under pressure, and a portion of the fuel flows back to the oil chamber in the upper part of the fuel injection pump through the oil holes. When the top surface of the plunger covers the upper edge of the oil inlet hole in the sleeve, the very small clearance between the plunger and the sleeve (0.0015–0.0025 mm) causes the pumping chamber at the top of the plunger to become a sealed oil chamber. As the plunger continues to rise, the oil pressure inside this pumping chamber increases rapidly. When the pumping pressure exceeds the spring force of the oil outlet valve plus the remaining pressure in the high-pressure oil pipe, the oil outlet valve is pushed open, and high-pressure diesel enters the high-pressure oil pipe, where it is injected into the combustion chamber through the injectors. 　　Oil return process: The plunger supplies oil upward; when it moves upward to the inclined groove on the plunger (the stop supply point) that connects with the oil return hole on the sleeve, the low-pressure oil circuit in the pumping chamber becomes connected to the central hole, the radial holes, and the inclined groove on the plunger head. As a result, the oil pressure drops suddenly, and the outlet valve closes rapidly under the force of the spring, thereby stopping the supply of oil. Thereafter, the plunger moves upward again; once the protruding part of the cam has passed by, the plunger moves downward under the action of the spring. At this point, the next cycle begins. 　　A plunger pump is explained based on the principle of a plunger. It has two check valves, one on each side, with opposite directions of flow. When the plunger moves in one direction, negative pressure is created inside the cylinder; at this point, one of the check valves opens and liquid is drawn into the cylinder. When the plunger moves in the opposite direction, the liquid is compressed and the other check valve opens, allowing the liquid that was drawn in to be discharged. This mode of operation results in continuous oil supply after continuous movement. 　　The original text is from Aotuoshi’s official website: http://www.aotuoshi.com