Common air compressor model marking basis and method

Twenty-first Century air compressor market competition is fierce, consumers in the purchase of products, often the machine quality and price included in the purchase standard. Therefore, this article will be common in the market a variety of labeling methods to make a description, in order to protect the interests of consumers to do a force.

1. four basic marking methods

1. Motor horsepower is used to indicate that this was feasible when the early air compressor technology was not developed. However, with the continuous development of technology, even if the same motor is used now, the amount of air discharged by the actual air compressor will be very different due to the pressure, air compressor manufacturer and model size. Therefore, it is the most irresponsible practice to mark only the motor horsepower on the catalog.

2. The piston displacement amount (Piston displacement) indicates that since this is the design data of the air compressor, only the cylinder size needs to be multiplied by the number of revolutions. Therefore, this data is the easiest to obtain and is also used by many manufacturers to mark. There is no certain relationship between this theoretical value and the actual gas output, depending on the technical ability of the manufacturer.

3. Inlet volume (Inlet volume) is usually measured by aperture meter (Orifice meter) on the air inlet side. At present, it is only used to indicate the size of centrifugal air compressor. The unit used is ICFM, which is more accurate than the first two methods, but it is still higher than the actual gas output because internal losses are not included.

4. The free air output (Freeair delivery) indicates that this method is measured on the outlet side by an aperture flow meter. Due to its accuracy, it has become the world's main standard to measure the actual air output of air compressors, such as ISO,ASME,JIS, etc. However, in some Japanese manufacturer catalogues, F.A.D. is used to mark, but Nominal is added.

capacity, it is generally understandable to say that this F.A.D. is not real, but just a design value.

Unfortunately, it is one thing to have standards, and it is another thing to have them. Therefore, unless the standards on which they are based are stated in black and white on the original catalog, their credibility will be greatly reduced.

2. actual air output under different working conditions

the actual air output refers to the air output measured at the outlet of the air compressor (after the after-cooler), taking into account all losses, usually expressed as Free Air Delivery.

The so-called free air volume refers to the volume of air compressed by the compressor and the free air condition (temperature, pressure, humidity, etc.) of the inlet.

Therefore, even if the same test standard is used, the number expressed will differ by more than 20% due to the different "free air" used. The following are some of the commonly used free air conditions:

1. Normal condition (Normal Condition): method of representation: Nm & sup3;/min (or indicate the gas inlet condition used in the test)

air condition: 760mmHg, 0OC, 0% RH Volume index: 1.00

2. Standard condition (Standard Condition): representation method: SCFM (or indicate the gas inlet condition used in the test)

air condition: 1bar, 20 0C, 0% RH Volume index: 1.05 (approx.)

3. Actual condition (Actual Condition): representation method: ACFM,ICFM (or indicate the gas inlet condition used in the test)

air condition: 14.4psi, 35 0C, 60% RH Volume index: 1.20 (approx.)

the same amount of air, as long as the use of different air conditions, you can increase the number by 20%.

3. the actual air output tested under different pressures

the value of the actual air output (FAD) is related to the reference air condition and also to the pressure under which the test is performed.

For example, the actual air output measured by a 55kW blower at 0.5barg is about 40m & sup3;/min, the actual air output measured by a 55kW micro-oil screw air compressor at 8barg is about 9.1 m & sup3;/min, while the actual air output measured at 13barg is about 6.8m & sup3;/min.

Therefore, when comparing the actual air output of air compressors of different brands with the same power, the pressure of the test flow should be considered. There is no strict theoretical calculation formula to convert, but there is a recognized empirical formula for reference.

For the oil-injected screw air compressor, if the same actual air output is still maintained when the pressure rises, the rotor speed needs to be increased, and at the same time, 6 to 7% of the motor power is consumed. For a completely oil-free screw air compressor, it is necessary to increase the power consumption by about 10%.

For example, suppose a 55kW micro-oil screw machine A measures an actual air output of 9.54m & sup3 at 7barg;/min, another 55kW micro-oil screw machine B measured the actual air output at 8bar to be 9.1 m & sup3;/min, is the efficiency of a high or B high?

According to the above empirical formula, A should still maintain 9.54 m & sup3 at 8barg;/min if the air output is unchanged, the power consumption needs to be increased by more than 6%, I .e. the specific energy of 55kW × 1.06=58.3 kW is respectively:

a:58.3kW÷9.54m³/min=6.11kW/(m³/min)

B :55kW÷9.1 m³/min=6.04kW/(m³/min)

(6.11-6.04)÷ 6.04 × 100%= 1.16% This means that the efficiency of B air compressor is 1.16% higher.

Motor power of 4. air compressor

the efficiency of the air compressor is related to the actual air output of the air compressor and the power consumed by the motor. The actual air output will vary greatly in value due to different test methods and representation methods, and there is a similar situation when examining the motor power of the air compressor. At the same time, the efficiency of the air compressor is also related to the motor service coefficient and motor efficiency.

1. Axis horsepower of specific pressure

people often use specific energy (Specific energy)-the power consumption per unit of air output to measure the efficiency of the air compressor. The power consumption here refers to the shaft horsepower of a specific pressure, which means that when the outlet pressure of the air compressor reaches a certain pressure point, the air compressor The power consumed by the main shaft. Since the pressure points selected by different manufacturers are different, the indicated shaft horsepower values are also different.

2. Service Factor (Service Factor)

the motor power of the air compressor refers to the nominal horsepower or rated power of the motor, but this is not equal to the actual power consumed by the motor. For manufacturers in Europe and China, the actual power consumption of motors is generally less than the rated power on famous brands, while manufacturers in the United States are accustomed to using smaller motors with a larger service coefficient such as 1.25,

at full load, the motor output can exceed 15% of the nameplate,

if the motor is marked as 100HP, its actual output may exceed 115HP. This breaks the old rule that the actual power consumption of the motor must be less than the rated power on the motor nameplate ".

Therefore, in general, for air compressors with the same horsepower, the air volume data of European brands is smaller than that of American brands for the above reasons. Now some manufacturers of European brands have begun to follow the example of the United States.

5. the efficiency of air compressor

as mentioned above, considering the efficiency of the air compressor, the test method should be considered, indicating the state, test pressure point, actual power consumption, etc. At the same time, the motor efficiency should also be considered, because the shaft horsepower is only the output part of the motor, and the electricity charge paid by the user is calculated according to the input power.

In this way, if you do not understand the standards used by each manufacturer in marking air compressors and selecting motors, it is almost meaningless to compare their efficiency with the information on their catalogs. In fact, even knowing all the details of each manufacturer is very difficult to compare, because the relationship between different standards is difficult to determine.