How to find the right size air compressor in China? 1/2
In order to reduce costs, more and more foreign manufacturers are coming to China in search of quality production equipment at reasonable prices. In this process, there are some confusions about the differences in equipment parameters and production execution standards. In order to improve the communication efficiency, DREAM not only provides reliable air compressor solutions, but also helps foreign buyers to understand the Chinese market through a series of articles, so that they can make the right choice.
Here are some basic facts about air compressors to help you to determine the right size air compressor. And we Illiterate some industry standards for you to understand the Chinese market for air compressors production.
First, to determine the size air compressor, we need to know the needs of air in our production. There are three parameters of compressor pressure(working pressure or discharge pressure), air flow (or air capacity, free air delivery ) and power are the most important parameters for the engineering to design, experiment and finalize the compressor. It is also the 3 basic elements of selection.
1.Pressure
Pressure is the amount of force applied perpendicular to the surface of an object per unit area. [wikipedia]
Common unit
International unit Pa (Pascal, abbreviated as “Pa”)
1MPa = 1000kPa = 10bar
1atm=0.101325MPa=1.01325bar=760mmHg≈10.33mH2O
1kg/cm2≈0.98bar
1MPa=≈145psi
Psi=pounds per square inch
The discharge pressure marked on the nameplate of the compressor is the rated discharge pressure, which is generally the maximum permissible discharge pressure.
Stable discharge pressure in the production process is important. It makes sure that the amount of compressed air released into the pipeline matches what the machines or tools use. The changes of the discharge pressure is essentially a change in the volume of compressed air.
(1) If the two are balanced, the discharge pressure is stable.
(2) If the two are not in balance, the discharge pressure changes.
When the discharged volume is larger than the consumed volume, the network pressure increases. After reaching a new balance, the pressure stays stable.
When the discharge volume is less than the consumption volume, the network pressure drops. It then reaches a new balance and stabilizes at this pressure.
If you notice that an air compressor rated at 8 bar cannot reach that pressure, it may be due to high air usage. This happens when the air consumed is more than what the machine can produce. Therefore, it is vital to choose a reasonable working discharge pressure.
2.Air Flow (or air capacity, free air delivery )
Air flow refers to the volume of gas discharged by a compressor per unit of time at the required discharge pressure.
Converted to the inlet state of the volume value. Commonly known as “exhaust volume” “gas volume” and air capacity or free air delivery and so on.
Expression of air compressor air flow
(1) The prescribed working conditions given in national standard GB19153-2019 are below.
Suction pressure : 0.1MPa (absolute pressure), suction temperature: 20 ℃, suction relative humidity: 0%.
In the calculation of air flow, converted to this working condition, the unit can be m³/min, L/min,m³/h, m³/s and L/s.
Many Chinese air compressor manufacturers provide their own working condition descriptions. For example, the latest product catalog from DREAM 2024 states that the flow rate of the product:
1. The value of the exhaust volume (temperature: 32° C, atmospheric pressure: 101.325KPa)
2. The discharge pressure is the pressure value after the check valve
If you are working in tough conditions like high heat, humidity, extreme cold, or dusty, please contact to a professional technician. They can help you with technical solutions and give you quotes.
(2) Standard working conditions IS0 (Internation Organization for Standardization) organization,
Suction pressure: 0.101325MPa, suction temperature: 0 ℃, suction relative humidity: 0%. In the calculation of air flow, converted to this condition, the unit is Nm³/min.
In addition, there is a part of the buyer's technical parameters working condition standard is FAD.
(3) Free Air Delivery (FAD) refers to the compressor after compression of the air
The free air delivery (FAD) is the volume of air compressed by the compressor, which is converted to the atmospheric condition at the air inlet of the site (suction temperature, suction pressure, suction relative humidity of the site).
The unit is m³/min.
You will find that you may get the same exhaust pressure from different Chinese suppliers but the air flow rate is not the same. This is because Chinese air compressor manufacturers will follow GB19153-2019.However, this standard allows for a 5% difference. This difference may be caused by the difference between the motor and the mainframe as well as the efficiency of the motor. You need to be patient when asking the supplier about the working conditions. Request a clear explanation of the calculation process. Also, ask for details about the motor design and the host specifications.
3.Power
Power is the amount of work done by an object in a unit of time,or power is a physical quantity that describes the speed of doing work, in W (watts).
Physical quantity, the unit is W (watts).
Industry commonly used power units are W (watts), kW (kilowatts).
In addition, there are HP (British horsepower, usually used in electric motors),
PS (metric horsepower, or metric horsepower, usually used in electric motors).
Unit conversion: 1HP = 0.75kW, 1PS = 0.735kW.
On the Chinese market, the exhaust pressure of the general air compressor is commonly used staging: 0.2MPa, 0.25MPa, 0.3MPa, 0.4MPa,
0.5MPa, 0.7MPa, 0.8MPa, 1.0MPa, 1.25MPa. 0.7MPa, 0.8MPa are the most common.
When you observe the selection parameter table of each manufacturer, you will find that.
(1) when the exhaust power is the same, the greater the exhaust pressure, the smaller theair flow.
(2) When the exhaust pressure is the same, the greater the power, the greater the volumetric flow;
(3) When the exhaust pressure is the same, the greater the power, the greater the volumetric flow.
(3) When the volume flow rate is the same, the greater the exhaust pressure, the greater the power.
(3) When the air flow is the same, the higher the discharge pressure, the higher the power.
The relationship between the three and the rotational speed (here the rotational speed refers to the rotational speed of the compressor host, not the rotational speed of the driving prime mover, excluding the acceleration/deceleration mechanism) are as follows
(1)When the power is the same, the higher the discharge pressure, the lower the speed, the lower the air flow;
(2)When the power is the same, the higher the discharge pressure, the lower the speed, the lower the air flow.
After we understand the three most important factors in determining the selection of air compressors, we need to understand the external factors affecting the efficiency of the compressor, and in the selection of the type of consideration, in order to prevent the machine can not meet the requirements of the work of the air. In the next article how to further select the right model according to the local working temperature and altitude and humidity.
