Air Compressor Selection Steps and Solutions
Time:2025-08-18
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01 Introduction to Air Compressors
An air compressor, commonly referred to as an air - compressor, takes ambient air as raw material and converts the mechanical energy of a prime mover (usually an electric motor) into the pressure energy of gas to meet the pressure required by the production process. There are many classifications of compressors. According to the working principle, they can be divided into positive - displacement compressors and dynamic compressors. The dynamic type mainly has two basic types: centrifugal and axial - flow. The working principle of a dynamic compressor is to increase the movement speed of gas molecules, convert the kinetic energy possessed by gas molecules into the pressure energy of gas, thereby increasing the pressure of compressed air.
02 Selection Principles of Air Compressors
The so - called rational selection of a compressor is to comprehensively consider the comprehensive technical and economic indicators such as the investment and operation costs of the compressor unit and the compressor station, so as to make it conform to the principles of economy, safety and applicability. Specifically, it includes the following aspects:
- It must meet the requirements of the flow rate and pressure required by the production process, that is, it requires that the operating condition point of the compressor (the intersection point of the device characteristic curve and the performance curve of the compressor) always operates in the high - efficiency interval, so that it saves power and is not easy to damage the components.
- The selected compressor should be small in volume, light in weight, inexpensive to manufacture, and have good characteristics and high efficiency.
- It has good anti - surge performance, stable operation and long service life.
- Simple in structure, convenient to operate, and accessories are easy to purchase.
- The selected compressor station has less engineering investment and low operation cost.
The selection of an air compressor is mainly based on the working pressure and flow rate of the starting system. The working pressure of the air source should be about 20% higher than the maximum working pressure in the pneumatic system, because the pipeline loss and local loss of the gas supply pipeline need to be considered. If the working pressure requirement in some places of the system is relatively low, a pressure reducing valve can be used for gas supply. The rated exhaust pressure of the air compressor is divided into low pressure (0.7 ~ 1.0Mpa), medium pressure (1.0 ~ 10MPa), high pressure (10 ~ 100Mpa) and ultra - high pressure (above 100Mpa), and can be selected according to actual needs. The commonly used pressure is generally 0.7 ~ 1.25Mpa.
03 Selection Steps of Air Compressors
(1) Compressor Performance Characteristics:
① Air characteristics: Local atmospheric pressure, local air relative humidity, etc.
② The diameter and content of solid dust particles contained in the air.
③ Air temperature: (°C)
④ Required flow rate (Nm³/min or Nm³/h)
a. Flow rate, commonly referred to as exhaust volume by domestic users. The flow rate refers to the amount of gas discharged by the air compressor per unit time under the required exhaust pressure, converted to the state of inlet air.
b. The unit of flow rate is: m³/min (cubic meters per minute) or L/min (liters per minute), 1m³ (cubic meter) = 1000L (liters);
c. Generally, the commonly used unit of flow rate is: m³/min (cubic meters per minute);
d. The flow rate is also called exhaust volume or rated flow rate.
(2) Pressure: Design pressure, maximum working pressure, working pressure.
There are many forms of expressing pressure units. Here we mainly introduce the pressure units commonly used by centrifugal air compressors:
① Working pressure, commonly referred to as exhaust pressure by domestic users. The working pressure refers to the maximum pressure of the gas discharged by the air compressor;
② Commonly used working pressure units are: bar or MPa, 1bar = 0.1MPa;
③ Generally, users often refer to the pressure unit as: kgf/cm², 1bar = 1kgf/cm².
(3) Pipeline system data (pipe diameter, length, types and quantities of pipeline accessories, etc.).
When designing and arranging pipelines, the following matters should be noted:
① Reasonably select the pipeline diameter. A larger pipeline diameter results in lower air velocity and less resistance loss under the same flow rate, but the price is high; a smaller pipeline diameter will lead to an increase in resistance loss, which will increase the power of the selected compressor, and the cost and operation cost will increase accordingly. Therefore, it should be comprehensively considered from technical and economic perspectives.
② The air supply pipeline and its pipe joints should consider the maximum pressure they can withstand.
③ The pipeline arrangement should be as straight as possible, minimize the accessories in the pipeline and the length of the pipeline as much as possible. When bending is necessary, the bending radius of the elbow should be about 3 - 5 times the pipeline diameter, and the angle should be as large as possible greater than 90°C.
④ The outlet pipeline of the compressor must be equipped with a gas supply valve and a check valve. The valve is used to control the working point of the compressor. The check valve prevents the compressor from reversing when the pressure in the pipeline is higher than the outlet of the compressor due to a sudden increase in air pressure, so as to prevent damage to the impeller and the reversal of the motor.
① Air characteristics: Local atmospheric pressure, local air relative humidity, etc.
② The diameter and content of solid dust particles contained in the air.
③ Air temperature: (°C)
④ Required flow rate (Nm³/min or Nm³/h)
a. Flow rate, commonly referred to as exhaust volume by domestic users. The flow rate refers to the amount of gas discharged by the air compressor per unit time under the required exhaust pressure, converted to the state of inlet air.
b. The unit of flow rate is: m³/min (cubic meters per minute) or L/min (liters per minute), 1m³ (cubic meter) = 1000L (liters);
c. Generally, the commonly used unit of flow rate is: m³/min (cubic meters per minute);
d. The flow rate is also called exhaust volume or rated flow rate.
(2) Pressure: Design pressure, maximum working pressure, working pressure.
There are many forms of expressing pressure units. Here we mainly introduce the pressure units commonly used by centrifugal air compressors:
① Working pressure, commonly referred to as exhaust pressure by domestic users. The working pressure refers to the maximum pressure of the gas discharged by the air compressor;
② Commonly used working pressure units are: bar or MPa, 1bar = 0.1MPa;
③ Generally, users often refer to the pressure unit as: kgf/cm², 1bar = 1kgf/cm².
(3) Pipeline system data (pipe diameter, length, types and quantities of pipeline accessories, etc.).
When designing and arranging pipelines, the following matters should be noted:
① Reasonably select the pipeline diameter. A larger pipeline diameter results in lower air velocity and less resistance loss under the same flow rate, but the price is high; a smaller pipeline diameter will lead to an increase in resistance loss, which will increase the power of the selected compressor, and the cost and operation cost will increase accordingly. Therefore, it should be comprehensively considered from technical and economic perspectives.
② The air supply pipeline and its pipe joints should consider the maximum pressure they can withstand.
③ The pipeline arrangement should be as straight as possible, minimize the accessories in the pipeline and the length of the pipeline as much as possible. When bending is necessary, the bending radius of the elbow should be about 3 - 5 times the pipeline diameter, and the angle should be as large as possible greater than 90°C.
④ The outlet pipeline of the compressor must be equipped with a gas supply valve and a check valve. The valve is used to control the working point of the compressor. The check valve prevents the compressor from reversing when the pressure in the pipeline is higher than the outlet of the compressor due to a sudden increase in air pressure, so as to prevent damage to the impeller and the reversal of the motor.
04 Selection of Working Pressure (Discharge Pressure)
When a user is preparing to purchase a compressor, first determine the working pressure required by the gas - using end, add a margin of 1 - 2bar, and then select the pressure of the air compressor. (This margin considers the pressure loss from the installation point of the air compressor to the pipeline of the actual gas - using end. The pressure margin is appropriately considered between 1 - 2bar according to the length of the distance.)
Of course, the size of the pipeline diameter and the number of bends are also factors affecting the pressure loss. The larger the pipeline diameter and the fewer the bends, the smaller the pressure loss; conversely, the greater the pressure loss.
Therefore, when the distance between the compressor and the pipeline of the gas - using end is too far, appropriately increase the diameter of the main pipeline. If the environmental conditions meet the installation requirements of the air compressor and the working conditions permit, the air compressor can be installed near the gas - using end.
Of course, the size of the pipeline diameter and the number of bends are also factors affecting the pressure loss. The larger the pipeline diameter and the fewer the bends, the smaller the pressure loss; conversely, the greater the pressure loss.
Therefore, when the distance between the compressor and the pipeline of the gas - using end is too far, appropriately increase the diameter of the main pipeline. If the environmental conditions meet the installation requirements of the air compressor and the working conditions permit, the air compressor can be installed near the gas - using end.
05 Selection of Flow Rate
① When selecting the flow rate of the air compressor, first understand the flow rates of all gas - using equipment, and multiply the total flow rate by 1.2 (that is, a 20% margin);
A. If the minimum, normal, and maximum flow rates are given in the production process, consider the maximum flow rate.
B. If only the normal flow rate is given in the production process, a certain margin should be considered.
C. The flow rate unit should be unified. Currently, the flow rate unit used in China is: Nm³/min or Nm³/h. In general, industrial air compressors can ignore the leakage in the pipeline system in the process flow, but must consider the impact of process changes on the flow rate.
② For new projects, the flow rate value provided by the design institute can be used for selection;
③ Understand the flow rate parameters of the gas - using equipment from the supplier of the gas - using equipment for selection;
④ For the transformation of the air compressor station, reference can be made to the parameters and combined with the actual gas - using situation for selection;
In recent years, the compressor industry has designed and developed many high - efficiency and energy - saving products. However, currently, in various fields of the national economy, due to unreasonable selection, many compressors are in an unreasonable operation state, with low operation efficiency, wasting a large amount of energy. Some compressors cannot be used at all due to unreasonable selection, or the maintenance cost increases during use, and the economic benefit is low. Therefore, proper selection can protect the unit, extend the service life of the unit, reduce the number of maintenance times, lower the operation cost, save energy consumption, and avoid unplanned downtime.
A. If the minimum, normal, and maximum flow rates are given in the production process, consider the maximum flow rate.
B. If only the normal flow rate is given in the production process, a certain margin should be considered.
C. The flow rate unit should be unified. Currently, the flow rate unit used in China is: Nm³/min or Nm³/h. In general, industrial air compressors can ignore the leakage in the pipeline system in the process flow, but must consider the impact of process changes on the flow rate.
② For new projects, the flow rate value provided by the design institute can be used for selection;
③ Understand the flow rate parameters of the gas - using equipment from the supplier of the gas - using equipment for selection;
④ For the transformation of the air compressor station, reference can be made to the parameters and combined with the actual gas - using situation for selection;
In recent years, the compressor industry has designed and developed many high - efficiency and energy - saving products. However, currently, in various fields of the national economy, due to unreasonable selection, many compressors are in an unreasonable operation state, with low operation efficiency, wasting a large amount of energy. Some compressors cannot be used at all due to unreasonable selection, or the maintenance cost increases during use, and the economic benefit is low. Therefore, proper selection can protect the unit, extend the service life of the unit, reduce the number of maintenance times, lower the operation cost, save energy consumption, and avoid unplanned downtime.
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