Working principle of hydraulic pumps

Thread Content

　　A hydraulic pump is a hydraulic component that provides pressurized fluid for hydraulic transmission; it is a type of pump. Its function is to convert the mechanical energy of a power source (such as internal combustion engines and electric motors) into the pressure energy of a liquid. The cam is rotated by an electric motor. When the cam pushes the plunger upward, the sealed volume formed by the plunger and the cylinder body decreases, and the oil is forced out of this sealed volume and discharged to the desired location through a one-way valve. When the cam rotates to the descending part of the curve, the spring forces the plunger downward, creating a certain degree of vacuum; under atmospheric pressure, the oil in the tank enters the sealed volume. The cam causes the plunger to move up and down continuously, resulting in the sealing volume decreasing and increasing periodically, which enables the pump to continuously draw in oil and discharge it. The diagram shows the working principle of a single-plunger pump. 　　Performance parameters The hydraulic pump is the power element of a hydraulic system; its function is to supply pressurized oil to the hydraulic system. From the perspective of energy conversion, it transforms the mechanical energy output by the prime mover into liquid pressure energy that is easy to transmit. A hydraulic motor is a type of actuator that converts the pressure energy of the input fluid into mechanical energy in the form of rotation of the output shaft, thereby enabling it to drive a load and perform work. 　　Based on their structural design, hydraulic pumps and hydraulic motors can be classified into types such as gear-type, vane-type, and piston-type. 　　1. Hydraulic pump pressure The operating pressure of a hydraulic pump refers to the pressure at which the pump (or motor) delivers or receives oil during actual operation, and it is determined by the external load. 　　Rated pressure refers to the highest pressure at which continuous operation is possible under normal operating conditions, as specified by the testing standards. Its size is limited by its service life; if it operates at a pressure exceeding the rated value, the pump (or motor) will have a shorter service life than designed. When the operating pressure exceeds the rated pressure, it is referred to as overload. 　　2. Rotational speed The operating rotational speed refers to the actual speed at which the pump (or motor) rotates while in operation. 　　The rated speed refers to the highest speed at which continuous and normal operation is possible under rated pressure. If the pump operates above its rated speed, it will result in insufficient oil suction, causing vibration and excessive noise; moreover, the components will suffer from cavitation damage, reducing their lifespan. 　　The minimum stable speed refers to the lowest speed allowed for the motor to operate properly. At this speed, the motor does not exhibit crawling. 　　3. Displacement and flow rate 　Displacement refers to the volume of liquid discharged (or pumped in) per rotation of the pump (or motor), as resulting from the changes in the geometric dimensions of the sealed chamber; the common unit used is ml/r (i.e., milliliters per revolution). A pump whose displacement can be adjusted is called a variable-displacement pump (or variable-displacement motor), while one whose displacement cannot be changed is called a fixed-displacement pump (or fixed-displacement motor). 　　Actual flow rate refers to the flow rate at the outlet or inlet when the pump (or motor) is in operation. Due to internal leakage within the pump itself, its actual flow rate is lower than the theoretical flow rate. Since the motor itself also has internal leakage, in order to achieve the specified speed, the actual input flow rate must be greater than the theoretical flow rate in order to compensate for the leakage. 　　4. Efficiency Volume efficiency, for hydraulic pumps, refers to the ratio of their actual flow rate to their theoretical flow rate. For hydraulic motors, it refers to the ratio of their theoretical flow rate to their actual flow rate. 　　Mechanical efficiency, for hydraulic pumps, refers to the ratio of their theoretical torque to the actual input torque. For a hydraulic motor, the actual torque it outputs is the torque obtained after the theoretical torque has overcome the friction force; therefore, its mechanical efficiency is the ratio of the actual output torque to the theoretical torque. 　　Overall efficiency refers to the ratio of the output power to the input power of a pump (or motor). The overall efficiency is equal to the product of volumetric efficiency and mechanical efficiency.