The hydraulic pump is an energy conversion device, which converts the mechanical energy of the driving motor into the pressure energy of the oil to meet the needs of the actuator to drive the external load, and is the main component of the power mechanism of the hydraulic machine.

How hydraulic pumps work?

The working principle of the hydraulic pump used in the current hydraulic system is almost the same, that is, the oil absorption and oil pressure are realized by the volume change rate of the hydraulically sealed working chamber, so it is called a positive displacement hydraulic pump.

The working principle of the positive displacement hydraulic pump is very simple. Take a single plunger hydraulic pump as an example, just like our common medical syringe, and it can be equipped with an automatic distribution device.

How to choose a hydraulic pump?

The hydraulic pump is the power source of the hydraulic system. We should choose a pump that can adapt to the pressure generating circuit required by the actuator, and at the same time fully consider other factors to ensure that the selected pump can run stably for a long time.

Whether to require variables

According to different structures, hydraulic pumps can be classified into vane pumps, gear pumps, plunger pumps and screw pumps (not commonly used). According to whether the flow rate changes, it can be divided into quantitative pumps and variable pumps.

For constant speed, choose quantitative pump, there are a gear pump and double-acting vane pump; if the flow rate of the pump is required to be variable, single-acting vane pump and plunger pump can be selected.

System pressure

When choosing a hydraulic pump, it should be considered that the pump has a certain pressure reserve, and the rated working pressure of the hydraulic pump should be 10%-20% higher than the system working pressure.

Generally speaking, under low pressure (high pressure less than 7Mpa), any type of pump can be used. The plunger pump should be selected in the high pressure (high pressure less than 60Mpa) working condition, and the gear pump is used more in the medium pressure (high pressure less than 32Mpa) working condition. Vane pumps and screw pumps are more economical to use under low pressure.

Working environment

In terms of resistance to pollution sources, gear pumps have the best resistance to pollution, followed by vane pumps. Piston pumps have the highest demands on oil cleanliness.

Noise index

Under the same working conditions, the noise generated by the hydraulic pump varies with the type of pump. The external gear pump and plunger pump are the loudest, while the screw pump is the least, and the noise of the vane pump and the internal gear pump is in between.

The noise generated by the hydraulic pump increases with the increase of pressure and displacement, and also increases with the increase of speed.

Efficiency 

The efficiency of the hydraulic pump is generally affected by the following factors: size, geometric clearance and the matching accuracy of the parts in the hydraulic pump; the viscosity and performance of the oil; the working pressure and speed. In order to obtain higher volumetric efficiency, when selecting a hydraulic pump, it is necessary to understand the allowable limits of the internal parts of the hydraulic pump.

In general, axial piston pumps have the highest overall efficiency, followed by vane pumps, and finally gear pumps. For pumps with the same structure, the pump with large displacement has high total efficiency; the pump with the same displacement has the highest total efficiency under rated operating conditions.

Application

Vane pumps are generally only used in non-regulated hydraulic systems, such as hydraulic systems of machine tools, hydraulic presses, vehicles, construction machinery and plastic injection machines.

Gear pumps are mostly used in machine tools, construction machinery, mining machinery, and agricultural machinery.

Piston pumps, especially axial piston pumps, are widely used in high-power hydraulic systems that require high pressure, large flow and need to be adjusted, such as forging machinery, transportation machinery, mining machinery, metallurgical machinery, ships, aircraft, etc.

Last few words

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