Explanation of common terms used in air compressor

Explanation of common terms used in air compressor

1. Compressed media

　　 Why use air as the compression medium? Because the air is compressible, clear and transparent, and easy to transport (non-condensing), harmless, safe and inexhaustible.

　　 Nature of air:

　　Ⅱ, "level" and "section

　　 Dry air composition: Nitrogen (N2) 78.08% Oxygen (O2) 20.93% Carbon dioxide (CO2) 0.03%

　　Density: ρ=1.293kg/m3 at 0℃ and 760mmHg column.

　　 In a positive displacement compressor, after each compression in the working chamber, the gas enters the cooler for a cooling, which becomes a "stage". In a power compressor, the compressor usually enters the cooler for cooling after two or more impeller compressions. The several compression "stages" for each cooling are collectively called a "section".

　　 In Japan, the "stage" of the positive displacement compressor is called "duan". Individual regions and individual documents in China are affected by this, and the "stage" is also called "duan".

　　 Three, pressure

　　The pressure referred to in the compressor industry refers to the pressure (P)

　　 The force of 1N acting on the area is 1Pa, that is, 1Pa=1N/㎡. Pa is the basic unit of pressure. When the pressure value is large, kPa (1kPa=1000Pa) and MPa (1MPa=1000000Pa) can be used.

　　Ⅰ, standard atmospheric pressure (atm)

　　Ⅱ, gauge pressure and absolute pressure

　　① The pressure measured by the pressure gauge is the gauge pressure, which is the difference between the pressure in the container and the local atmospheric pressure. It is the pressure measured at the zero point of atmospheric pressure, expressed in Pg.

　　②The pressure with absolute vacuum as the zero point is called absolute pressure, which is the sum of the pressure in the container and the local atmospheric pressure, expressed in Pa. The relationship between gauge pressure and absolute pressure:

　　 gauge pressure + atmospheric pressure = absolute pressure

　　 The discharge pressure usually given on the compressor nameplate is the gauge pressure.

　　Ⅲ, working pressure

　　 suction and discharge pressure refers to the suction and discharge pressure of an air compressor.

　　 The gas pressure measured at the inlet flange of the working chamber of the first-stage cylinder of the compressor and the outlet flange of the working chamber of the last-stage cylinder is called the suction and discharge pressure of the compressor.

　　In some occasions, the compressor discharge pressure is also called "back pressure"

　　 Screw air compressor suction and discharge pressure refers to the suction and discharge pressure of the entire air compressor. Generally speaking, the working pressure of the air compressor refers to the discharge pressure.

　　Ⅵ. Conversion of pressure units commonly used in air compressors

　　 1MPa (megapascals) = 1000kPa (kilopascals) = 1000000Pa (pascals)

　　1bar (bar) = 0.1MPa

　　1atm (standard atmospheric pressure)=0.1013MPa

　　=1.013bar

　　=760mmHg

　　=10.33mH2O

　　1kgf/cm2 (engineering kilogram force)=0.981bar

　　=0.0981Mpa

　　1psi (bf/in2)=0.07031kgf/cm2

　　=0.06893 bar

　　=6.893kpa

　　1MPa=145psi (bf/in2) pounds per square inch, it is commonly used in product parameters in English-speaking countries such as Europe and the United States.

　　 The "kg" usually said in the air compressor industry means "bar".

　　 Four, compression

　　Ⅰ. Isothermal compression: A compression method that keeps the temperature constant when the gas is compressed.

　　Ⅱ. Adiabatic compression: A compression method under an adiabatic state that neither heats nor removes heat from the outside.

　　Ⅲ. Polygonal curve compression (compression method actually used): It is a compression method that dissipates part of the heat generated and exchanges heat with the outside, which is different from isothermal compression and adiabatic compression.

　　 5. Compression ratio (pressure ratio, pressure ratio)

　　Ⅰ, internal compression ratio (ie internal pressure ratio)

　　 The ratio of the final pressure (absolute pressure) to the initial pressure (absolute pressure) of the gas after internal compression.

　　Ⅱ, external compression ratio (ie, external pressure ratio)

　　The ratio of the compressor outlet discharge pressure (absolute pressure) to the inlet suction pressure (absolute pressure). For screw air compressors, the internal compression ratio refers to the pressure ratio between the suction and exhaust ports of the screw main engine (absolute pressure), and the external compression ratio refers to the pressure ratio between the suction and exhaust pipes of the air compressor (absolute pressure) .

Generally speaking, the compression ratio of an air compressor refers to the external compression ratio, the suction pressure refers to the local atmospheric pressure, and the exhaust pressure refers to the rated working pressure of the air compressor. For example, the exhaust pressure of the air compressor is 8bar, then the compression The ratio is 9.

　　 For a multi-stage compressor, the pressure ratio is also called the total pressure ratio, which refers to the ratio of the discharge pressure measured at the final stage exhaust pipe connection to the suction pressure measured at the first stage intake connection pipe. The ratio of the nominal suction and discharge pressures of the corresponding stages is called the pressure ratio of the stage.

　　 Six, volume flow

　　 Volume flow is also called displacement or nameplate flow in China. Generally speaking, under the required exhaust pressure, the volume of gas discharged by the air compressor per unit time is converted to the intake state, that is, the suction pressure at the first-stage intake pipe and the suction temperature and humidity. Volume value. That is the volume of inspiration. According to national standards, air compressors are qualified when the actual displacement of the air compressor is ±5% of the nominal flow.

　　 If the speed does not change, the pressure change theoretically does not affect the displacement, specifically, it affects the volume flow rate, not the mass flow rate. Because what we generally call the exhaust volume refers to the intake air flow, there is no change.

　　 Seven, gas oil content

　　Ⅰ. The mass of oil (including oil droplets, suspended particles, and oil vapor) contained in a unit volume of compressed air is converted to an absolute pressure of 0.1MPa, a temperature of 20°C, and a relative humidity of 65%. Unit: mg/m3 (refers to absolute value).

Ⅱ. ppm is a symbol that represents the content of trace substances in the mixture (ppm is the abbreviation of part per million in English), which refers to the number of parts per million or parts per million (part-mass ratio ppmw and volume ratio ppmv ) (Refers to the ratio).

　　 What we usually call ppm is the mass ratio. (One millionth of 1kg is milligram)

　　1ppmw=1.2mg/m3(Pa=0.1MPa, t=20℃, φ=65%)

Generally, the exhaust oil content of oil-injected screw air compressors is less than 5ppm, but the exhaust gas of centrifuges and oil-free machines is oil-free. Considering the oil particles originally contained in the air, it is impossible to reach 100% oil-free of.

　　 8. Dew point unit ℃ (Celsius)

The humid air is cooled under equal pressure, so that the unsaturated water vapor originally contained in the air becomes the temperature of saturated water vapor. In other words, when the temperature of the air drops to a certain temperature, the original unsaturated water vapor contained in the air is reduced. When the saturated state is reached (that is, the water vapor starts to liquefy and the liquid condenses), this temperature is the dew point temperature of the gas.

　　Pressure dew point means that when a gas with a certain pressure is cooled to a certain temperature, the unsaturated water vapor contained in it becomes saturated water vapor and precipitates. This temperature is the pressure dew point of the gas.

　　Atmospheric dew point refers to the temperature at which the gas is cooled to the temperature at which the unsaturated water vapor contained in it becomes saturated water vapor and precipitates under standard atmospheric pressure. In the air compressor industry, the dew point represents the degree of dryness of the gas.

　　 Nine, temperature

　　Temperature refers to a method of measuring the energy level of a substance at a certain time. (Or more simply, how hot or cold a certain thing is). The temperature range is based on the freezing and boiling points of water. On a Celsius thermometer, the freezing point of water is 0°C and the boiling point is 100°C. On a Fahrenheit thermometer, the freezing point of water is 32 °F and the boiling point is 212 °F. Conversion formula:

　　Fahrenheit (°F)=32+Celsius (°C)×9/5

　　10. Altitude

　　 Measured vertically upwards at sea level, altitude simply refers to the height above sea level. Elevation is an important factor in compressor engineering, because the higher the altitude, the thinner the air becomes and the lower the absolute pressure becomes.

　　Since the air at high altitude is relatively thin, the cooling effect of the motor is relatively poor, which makes the standard motor can only operate within a certain altitude.

　　 Eleven, working conditions.

The state parameters of the compressor's intake and exhaust pressure and intake temperature are called the compressor's "working condition", and the parameter working condition marked on the compressor nameplate is called the "rated working condition", which deviates from the "rated working condition". It is called "variable conditions".

　　12. Specific power

　　 refers to the power consumed per unit volume flow of the compressor. It is an important indicator for evaluating compressor energy efficiency. (Compress the same gas, under the same exhaust pressure)

　　13, protection level

　　 is a value indicating the degree of airtightness of electrical equipment against dust, foreign matter, and water, expressed in IPxx (xx are two Arabic numerals)

　　14, explosion-proof grade

　　 When explosive gas, steam, liquid, combustible dust and other places may cause fire or explosion hazard, the actuator must be explosion-proof requirements, and the explosion-proof form and category must be selected according to different application areas. The explosion-proof level can be indicated by the explosion-proof mark Ex and the explosion-proof content. The contents of the explosion-proof mark include: explosion-proof type + equipment category + (gas group) + temperature group.

　　 Fifteen, electrical and other terms

　　Ⅰ, power

　　Ⅱ, current

　　Ⅲ, voltage

　　Ⅳ, phase

　　Ⅴ, frequency

　　Ⅵ, frequency conversion. That is to change the frequency, in the application of air compressor, by changing the frequency of the power supply to change the speed of the motor, so as to achieve the purpose of adjusting the flow. Since the flow rate can be adjusted to 0.1bar through frequency conversion, the useless work is greatly reduced and energy saving is achieved.

　　Ⅷ, direct connection. Direct coupling, in the air compressor industry, refers to coupling with a shaft.

　　Ⅸ, loading/unloading. The working state of an air compressor generally means that the air compressor has a complete suction and exhaust process in the loading state, otherwise it is in the unloading state.

　　Ⅹ, air cooling/water cooling, refers to the cooling method.

　　Ⅺ, noise; unit: dB(A) (decibel).

　　16. Knowledge of motors

　　Ⅰ. How to indicate the model of small and medium asynchronous motors.

　　Ⅱ, motor installation type code.

　　Ⅲ. Insulation class and allowable temperature rise of the motor (altitude ≤1000m).

　　Ⅳ, the way of motor outlet;

　　Ⅴ. The relationship between the synchronous speed of the motor, the electric frequency and the number of poles;

　　Ⅵ. The safe use factor of the motor.