Selection of working pressure（discharge pressure）:

When we are ready to choose a air compressor, we must identify the pressure that the air appliance required. Then we can choose the working pressure of the compressor according to the required pressure added margin of 1-2bar.(The margin is the pipe pressure loss from the compressor site to the gas appliance. It can be chosen properly between 1 bar and 2 bar according to the distance.) Of course, the size of the pipe diameter and the number of the turning points are also factors affecting the pressure loss: the larger the pipe diameter and the less the turning points, the smaller the pressure loss; on the contrary, the greater the pressure loss.

Therefore, the size of the main pipe diameter should be enlarged if the distance between the compressor and the gas appliances. The compressor should be mounted near the gas appliances if the environment meets the installation requirements and the operating conditions are permission.

Selection of the volume flow:

① Identify the volume flow required by all gas appliances and the total flow multiplied 1.2(with the margin 20%) is the volume flow of the compressor.

② The volume flow provided by the design institute can be look as the volume flow of the compressor in a new project.

③ Identify the volume flow required by the gas appliance through its suppliers.

④ Refer to the original parameter and the actual usage in the reform of air compressor station.

It’s beneficial for users and compressor to select suitable model. It’s a waste to choose too large compressor. And there will be some disadvantages if the compressor is chosen too small. For example, it will make the compressor in the state of loading for a long time, the compressed gas be not enough, the pressure doesn’t rise, etc.

The relationship among power, working pressure and volume flow：

In the case of constant power, if the rotational speed changes, the working pressure and volume flow will change correspondingly.

For example: the volume flow of a compressor of 22 KW with the designed working pressure 7 bar is 3.8 m3/min, and the rotational speed can be calculated according to the machine head technology curve graph. When the working pressure is 8 bar, the rotational speed must decrease(otherwise, the driving motor will be overload), and then the volume flow is 3.6 m3/min. The rotational speed decreases and the volume flow decreases correspondingly, and so on.

Selection of the power:

It’s right if the power supply capacity can meet the need of the matching driving motor in the conditions of satisfying the working pressure and volume flow.

Therefore, the steps to select a compressor：first, identify the working pressure, then select the volume flow, identify the power in the end.