The Working Principle And Characteristics Of Hydraulic Pump

Hydraulic pump and hydraulic motor are energy conversion components in the hydraulic transmission system, hydraulic pump driven by the prime mover, the input mechanical energy into the oil pressure energy, and then in the form of pressure, flow into the system, it is the heart of the hydraulic transmission, but also the power source of the hydraulic system.
In the hydraulic system, the hydraulic pump and the hydraulic motor are positive displacement, relying on volume changes to work.
1. Working principle of hydraulic pump
Hydraulic pumps rely on the principle of sealing volume change to work, so it is generally called positive displacement hydraulic pump, the figure shows the working principle of a single plunger hydraulic pump, in the figure, the plunger 2 installed in the cylinder block 3 to form a sealing volume a, the plunger under the action of spring 4 has been pressed on the eccentric 1.
The prime mover drives the eccentric 1 to rotate the plunger 2 to reciprocate, so that the size of the sealing volume a changes periodically.
When a is small and large, a partial vacuum is formed, so that the oil in the tank under the action of atmospheric pressure, through the suction pipe top open check valve 6 into the tank A to achieve oil absorption; On the contrary, when a changes from large to small, the full oil in the cavity of a will open the check valve 5 into the system to achieve oil pressure.
In this way, the hydraulic pump converts the mechanical energy input by the prime mover into the pressure energy of the liquid, and the prime mover drives the eccentric wheel to rotate continuously, and the hydraulic pump continuously absorbs oil and pressure oil.
2. Characteristics of hydraulic pump
Single plunger hydraulic pump has all the basic characteristics of positive displacement hydraulic pump:
(1) Has a number of sealed and can be periodically changed space. The output flow of the hydraulic pump is proportional to the volume change of this space and the number of changes per unit time, and has nothing to do with other factors. This is an important characteristic of positive displacement hydraulic pump.
(2) The pressure of the liquid in the tank * must be equal to or greater than the atmospheric pressure. This is the external condition that the positive displacement hydraulic pump can inhale the oil. Therefore, in order to ensure the normal oil absorption of the hydraulic pump, the oil tank * must be communicated with the atmosphere, or a closed pressurized oil tank is used.
(3) There is a corresponding flow distribution mechanism to separate the oil suction chamber and the liquid discharge chamber to ensure that the hydraulic pump regularly and continuously sucks and drains liquid. The structure principle of hydraulic pump is different, and its oil distribution mechanism is also different. Check valves 5 and 6 in Figure 3-1 are the oil distribution mechanism.
The oil chamber in the positive displacement hydraulic pump is called the oil suction chamber when it is in the suction. The pressure of the oil suction chamber depends on the oil suction height and the resistance of the oil suction line. If the oil suction height is too high or the resistance of the oil suction line is too large, the vacuum degree of the oil suction chamber will be too high and affect the self-priming capacity of the hydraulic pump.
When the oil chamber is under pressure, it is called the oil chamber. The pressure of the oil chamber depends on the external load and the pressure loss of the oil discharge pipeline. Theoretically, the oil discharge pressure has nothing to do with the flow of the hydraulic pump.
The theoretical flow rate of displacement hydraulic pump depends on the relevant geometric size and speed of hydraulic pump, and has nothing to do with the oil discharge pressure.
However, the oil discharge pressure will affect the internal leakage of the pump and the compression of the oil, thus affecting the actual output flow of the pump, so the actual output flow of the hydraulic pump decreases with the increase of the oil discharge pressure.
Hydraulic pumps are divided into quantitative pumps and variable pumps according to whether the volume of the oil that can be output per unit time can be adjusted; According to the structure form can be divided into gear type, blade type and plunger type three categories.