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## Screw air compressor:

A machine designed according to the working principle of twin screw (also known as male-female rotor) rotating to change the volume of gas. It can inhale natural air and complete the work through several internal processes. Eventually discharging compressed air to meet the pressure requirements. This machine is called screw air compressor.

## Working pressure of air compressor:

There are many ways to express the working pressure unit of air compressor. Here we mainly introduces the commonly used pressure indicator units of screw air compressor.

• 1) Working pressure: commonly known as exhaust pressure by domestic users. Work pressure refers to the highest pressure of air compressor exhaust gas
• 2) The commonly used work pressure unit is bar or Mpa, 1 bar = 0.1 Mpa
• 3) Generally, users usually call the pressure unit Kg (kg), 1 bar = 1 Kg
• 4) 145 psi = 1 Mpa

## Volume flow rate of air compressor:

• 1) Volume flow rate: which is often called free air delivery. Volume flow refers to the volume of gas discharged by air compressor per unit time under the required exhaust pressure, which is converted to the intake state.
• 2) Volume flow unit is m3/min (cubic/minute) or L/min (liter/minute), 1m3 (cubic) = 1000L (liter)
• 3) Generally speaking, the commonly used flow unit is m3/min (cubic/minute)
• 4) Volume flow is also called exhaust flow or nameplate flow in China
• 5) CFM is a unit of flow per cubic foot per minute.1CFM=28.316846592 L/MIN=0.028 CMM(cubic meter per minute). 1cfm=1.7m3/h

## Power of air compressor:

• 1) The power of air compressor refers to the nameplate power of the matched driving motor or diesel engine
• 2) The unit of power is KW (kilowatt) or HP (horsepower), 1KW=1.333HP.

## Selection of working pressure (exhaust pressure)

• margin of 1-2 bar:When the user is ready to purchase an air compressor, the first step is to determine the working pressure needed at the gas end, plus a margin of 1-2 bar<, and then select the pressure of the air compressor. (The margin is to consider the pressure loss from the installation site of the air compressor to the actual pipeline of the air end, and to consider the pressure margin between 1-2 bar according to the length of the distance.)
• the size of pipeline diameter :The larger the pipeline diameter , the smaller the pressure loss; conversely, the greater the pressure loss.
• the number of turning points :the fewer turning points, the smaller the pressure loss;

a Therefore, when the distance between the air compressor and the gas-end pipeline is too far, the diameter of the main pipeline should be enlarged appropriately. If the environmental conditions meet the installation requirements of the air compressor and the working conditions permit, it can be installed near the gas terminal.

## Selection of volumetric flow:

• 1)20% margin: When choosing the volumetric flow rate of air compressor, we should first know the volumetric flow rate of all Air-using equipment, multiply the total flow rate by 1.2 (i.e. enlarging the 20% margin);
• 2) New projects can be selected according to the flow value provided by the design institute;
• 3)Get the volumetric flow parameters of Air-using equipment from suppliers;
• 4)Change of air compressor station. The model can be selected by referring to the original parameters and actual gas use.

Therefor suitable type selection, which is beneficial to users and air compressor equipment. Excessive waste of type selection and too small type selection may result in long-term loading state or insufficient gas or pressure.

## The relationship between power and working pressure and volumetric flow:

under the condition of constant power, when the speed changes, volumetric flow and working pressure also change correspondingly

For example: When a 22KW air compressor is manufactured, the working pressure is determined to be 7bar, and the speed is calculated according to the technical curve of the compressor main engine, the exhaust volume is 3.8m3/min; when the working pressure is determined to be 8bar. The speed must be reduced (otherwise the driving motor will be overloaded). Then the exhaust volume is 3.6 m3/min; because the speed is reduced, the exhaust is reduced accordingly, and so on.

The selection of power is based on the condition that the working pressure and volume flow are satisfied, and the power supply capacity can meet the use power of the matched driving motor.

Therefore, the selection of air compressor steps are:1)the working pressure , 2)corresponding volume flow,3)the power supply capacity.

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