6, compress and compression ratio

1, compress

Heat insulation is compressed is one kind is in what quantity of heat of the gas in reducing a process does not arise to be passed into apparently or come out to reduce a process. Inside a completely adiabatic air cylinder afore-mentioned processes can become reality. Isotherm is compressed is in reducing a process gas maintains the compression with constant temperature one kind process.

2, compression ratio: (R)

Compression ratio is to point to those who take angry absolutely pressure to compressor exhaust is mixed than. Exemple: Into gas when sea level absolutely pressure is 0.1 MPa, exhaust pressure is absolutely pressure 0. 8MPa. Criterion compression ratio:


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The advantage that multistage reduces:

(1) , economic compress result;

(2) , drop exhaust temperature;

(3) , raise cubage coefficient;

(4) , to piston compressor, lower gas the thrust to the piston.


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7, compress medium

Why should compress medium with air?

Because air is compressible, clear and transparent, and carry go to the lavatory (do not condense) , those who take is harmless sex, safe, endless.

Inert gase is a kind of gas that does not remove chemistry to the environment, standard compressor can compress inert gase euqally. Dry nitrogen and carbon dioxide all are inert gase.

Airy property:

Do air part:

Nitrogen (N2) 78.03%

Oxygen (O2) 20.93%

Carbon dioxide (CO2) 0.03%

Molecular quantity: 28.96

Specific gravity: When column of 0 ℃ , 760mmHg, r0=1.2931kg/m3

Specific heat: When a 25 ℃ , atmosphere, cp=0.241 kilocalorie / Kg - ℃

H is in T ℃ , pressure (Mmhg) when, airy proportion:

The proportion of moist air, still should consider saturated vapor to divide pressure (0.378ψ , pb) .


1, pressure

This is the force of some unit area only, if unit of pressure of 1 Newton strength suffers to be 1 Pascal on square metre:

Namely: ㎡ of 1Pa = 1N/

1Kpa = 1, ㎡ of 000 Pa = 0.01 Kg/c

㎡ of 1Mpa = 106Pa = 10 Kg/ C

2, absolutely pressure

Absolutely pressure is to consider with complete vacuum or absolutely 0 values are compared, the environmental air that we live has the absolutely pressure of 0.1Mpa. On sea level, the air pressure that appearance pressure increases 0.1MPa can reach absolutely pressure. Loftier air pressure jumps over height low.

3, atmosphere force

Barometer is to be used at measuring atmospheric pressure. Should add appearance pressure to go up to be able to reach absolutely pressure.

Pressure of air of + of manometric pressure of absolutely pressure =

Atmosphere force is with mercury Mm is an unit normally, but any pressure unit can make likewise very good explanation:

0.1MPa of ≌ of ㎡ of =1.033kgf/c of water column of rice of = 10.33 of mercuric column of millimeter of = 760 of pressure of air of a physics.

Atmosphere is the same as the relation of height above sea level:

H= height above sea level,

P0= atmosphere (0 ℃ , 760mmHg)

4, pressure unit conversion:

Unit: MPa, psi (Bf/in2)



0.1Mpa of ≌ of 1kgf/c ㎡ =98.066KPa=0.098066MPa


1, temperature

Temperature is to point to measure some material to be in the method of sometime energy level. (or simpler say, some thing has how many heat or how many cold) .

Temperature limits is the freezing point according to water and boiling point. On the Centigrade thermometer, the freezing point of water is zero, boiling point is 100 degrees. On the Fahrenheit, the freezing point of water is 32 degrees, boiling point is 212 degrees.

From Fahrenheit changeover becomes centigrade: Fahrenheit =1.8 centigrade + 32, centigrade =5/9 (Fahrenheit - 32)

2, absolutely temperature

This is the temperature that explain with absolute zero as base point.

Base point zero is Fahrenheit 0 times 459.67 spend or centigrade 0 273.15 degrees

Absolute zero is the temperature that the temperature that shows from materially eliminate the place when all quantity of heat exists or the gas from theoretic some cubage shrink to exist to zero hour place.

3, cooling temperature is poor

Cooling temperature needs the term of the efficiency that is affirmatory condenser. Because condenser is impossible to achieve the efficiency of 100 % , we can measure the efficiency of condenser with cooling difference in temperature only.

Cooling temperature difference is the difference of the cold water that enters condenser or cold air temperature and the temperature after compressing air to cool.

4, intermediate condenser

Intermediate condenser is the compression between the level that is used in cooling multistage compressor and class the parts of an apparatus that air or gas make thermal drop small. Intermediate condenser enters below one class to compress air temperature to achieve through reducing reduce compress power to increase efficiency in order to conduce to.

Dew point and relative humidity

1, dew point and relative humidity

Just like temperature drops in the evening meeting generation is roric and same, compress the temperature inside air system to drop to also can produce hydrosphere. Dew point is in when moist air namely the temperature that vapor divides the refrigeration below the circumstance with constant pressure to saturation.

Is this why? The air that contains moisture content can contain the moisture content of certain amount only. If pass pressure or refrigeration to make bulk contractible, contain all moisture content without enough air, because this moisture separate out of over becomes condenser water.

The air that leaves aftercooler is completely saturated normally. The condenser water inside segregator showed this, because this air temperature has any reduce, can produce condenser water.

The humidity of set can consider as moist air place the weight of hydrous steam, namely: Of vapor weight and dry air weight than.

Relative humidity ψ


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When Ps=0, when ψ=0, call dry air;

Ps=Pb, when ψ=1, call saturated air.

Absolutely humidity- - the weight that 1m3 moist air contains vapor.


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2, saturated air

Should do not have again much hydrosphere to be able to be accommodated when air is medium, produced airy saturation, any pressurization or the separate out that drop in temperature to all can cause condenser water.

3, hydrosphere segregator

Hydrosphere segregator is to be used at collecting to be with eliminate in cooling process from inside air or gas condensation comes out the parts of an apparatus of water.

Receiver is to be used at storing compressor discharges those who put to compress air is amiable the container of body. Receiver is helpful for eliminating the pulse in vent-pipe road, when the ability that is more than compressor in demand, can rise to store and complement offer reduce airy effect.

4, drier

Drier is to be used at dry airy device. With our term, it is to use its to compress air drily. The air that leaves aftercooler is completely saturated normally, that is to say any dropping in temperature that can produce condenser water. Refrigerant type drier is compress airy temperature through reducing, analyse goes moisture, heat air to be close to original temperature again next.

Drier of second birth type is to make air passes the filter that contains chemical material to be divided with separate out water. This kind of device compares refrigerant type device more can adsorptive hydrosphere.


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Condition reachs tolerance

1, standard reference conditions

The definition of standard reference conditions is: Air is inspiratory pressure is 0.1MPa, temperature is 15.6 ℃ (Chinese industry definition is 0 ℃ ) the airy dimension that user system provides below condition. If need to use standard reference conditions, will reflect the operation condition with actual consideration, such as height above sea level, temperature and relative humidity will answer actual and inspiratory condition is changed into standard reference conditions.

2, normal air

Formulary pressure is 20 ℃ , relative humidity to be normal air for the air below 36 % condition for 0.1MPa, temperature. Normal air and standard air differ to depend on temperature and contain moisture content. There should be hydrosphere in air, once depart hydrosphere, tolerance will be reduced somewhat.

3, inspiratory condition

Compressor imports the air below condition.

4, height above sea level

By sea level perpendicular measure up, altitude just is the height that points to sea level above. Altitude has main factor in compressor engineering field, because be in height above sea level is higher, air becomes rarer, absolutely pressure becomes lower. Since the air on altitude is rarer, so the cooling effect of electromotor is poorer, this makes standard electromotor can confine moves inside certain height above sea level. The biggest concessional moving height above sea level of EP200 level set is 2286 meters.

5, the factor that affects capacity

Pj, Tj, height above sea level, N, V beyond, leak.

6, the influence of height above sea level to compressor

Height above sea level is higher, air is rarer, press absolutely lower, pressure ratio is higher, nd is bigger;

Height above sea level is higher, cooling effect is poorer, electric machinery temperature rise is bigger;

Height above sea level is higher, air is rarer, the oil gas of diesel engine is bigger than jumping over, n is smaller.

7, cubage discharge

Cubage discharge is to show in the compressor inside unit time inspiratory standard reference conditions issues airy discharge. With the unit: M3/min (stere / cent) express. Bid just shows with Nm3/min.

1CFM=0.02832m3/min or 1m3/min=35.311CFM   S- - standard reference conditions, A- - actual condition

8, clearance cubage

Clearance cubage is type of cubage of quantity of platoon of point out mistakes so that they can be corrected (move back and forth or screw) the volume that compressor stroke terminal remains, after air classics expands, the compression of this cubage returns air suction opening, produce tremendous effect to cubage coefficient.

9, laden coefficient

Of the biggest rated output that laden coefficient is the average output that points to the compressor inside some period of time and compressor than. Unwise practice sells the compressor of the user namely, as it happens satisfies the biggest requirement of the user, increase or a few tools or the pressure that leak can cause a works drop. To prevent this kind of situation, china suggests to use laden coefficient all the time for years: Take user system place to need the great value of tolerance, divide with 0.9 or the laden coefficient of 0.8. (or any users consider as a safety factor)

This kind of integrated tolerance chooses can the addition of the air requirement that attend to did not predict. Need not the investment of additional capital, can do extend of a few diminutive.

10, tolerance checks

(1) , cubage of air cylinder of reciprocating type compressor

The cubage of compressor air cylinder is the bulk that the cubage that shows the piston is mobile subtracts piston lever is had. It is to use minutely stere to express normally. The cubage of multistage compressor is the volume that the first class reduces only, because one by one carries the gas of all class,originate the first class.

(2) , test

Low-pressure nozzle test is a kind measure compressor place accurately to provide airy means. Law of this one party gets those who compress air and aeriform institute approbate, still check code name committee for ASME the sources of energy be accepted.

The description that uses low-pressure nozzle to check reciprocating type compressor is concerned in ASME PTC-9. Have in ASME PTC-10 describe about what use low-pressure nozzle to check dynamical formula compressor.


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Power and than power (comparing of specific power consumption, cubage is compared can)

1, compressor efficiency

Of the actual tolerance that cubage efficiency is compressor and academic tolerance cubage than, express with per cent.

Reducing efficiency is to reduce the power that needs actually to mensurable gas and academic power than. Academic power can press isothermal operating mode or adiabatic operating mode is calculated. Corresponding compression decide and efficiency can express with per cent. the compressor with respect to vapour drive or internal-combustion engine drive, mechanical efficiency is the horsepower of demonstrative result cent that points to compressor and the cent of apply the brake on the axis of horsepower than. the compressor with respect to electromotor drive, mechanical efficiency is to point to those who compress the demonstrative power inside air cylinder to be the same as the axial power of compressor to compare. Will express with per cent.

2, overall efficiency

The compression that overall efficiency is compressor the summation of efficiency and mechanical efficiency.

Compressor axis power (power of apply the brake) include: Gas is compressed result - demonstrative result, friction work

Rough calculation: Nad=1.634PjVm (K/k-1) [ε (K-1/k) - 1] Kw

Axis of =N of N electric machinery / η is passed, η passes (leather belt: 0.92 ~ 0.98, gear: 0.97 ~ 0.99)

In screw compressor, the axial power of wind cold compressor should increase the power of windward fan electric machinery.

3, cubage is compared can

Cubage comparing can be to show compressor is inspiratory inside unit time the power that unit tolerance place consumes, express with Kw/m3/min normally, below same exhaust pressure cubage is compared can smaller. Namely bad news work is little. This compressor efficiency is the measuring of the true efficiency of compressor.

Than power: Regulate operating mode:

Pj=1bar (A) , tj=20 ℃ , ψ=0, ℃ of T water =15

Pc =7bar (express) , water measures ≤2.5L/m3

Power is the work that unit time place does, such as horsepower (kilowatt) be decided to be 76Kg-m/ hour

Power is the index that measures in the changeover of the sources of energy.

To get the cost of power, we also must include time, for example: Expending money is not kilowatt however kilowatt hour.

Take horse power and change its into the cost that expends an user, we should use the following formula:

Noise and sound are evaluated

Noise is considered as rebarbative or the sound of interference.

The user is willing completely to sit in the discotheque all night, the appreciation side smoking is as high as the Disco music of 95 decibel by the side of, but mysterious is he cannot tolerate unexpectedly the following day the copycat noise of the 65 decibel in the morning. The user likes the noise of Disco and do not like the noise of copycat. Value of typical cocktail lounge a confusion of voices is 90 decibel, the noise of rock-and-roll team is 100 arrive between 138 decibel.

So what is decibel?

The definition of decibel can explain the logarithm that is ratio of pair of two kinds of energy (with 10 for the bottom) hind by with 10.

Increase what 10 decibel express energy to increase 10:1, increase 20 decibel to state capabilities adds 100:1, increase 30 decibel to increase 1000:1.

To our application, we are level of discussion sound power - the W1 reference point of set is 10-12, its formula became:

For example, if we have cause of a sound, issue the power class of watt of a 10-5, that power is:

Carry on the back when ear to noise, people discovery is auditive automatically “ listens the noise that is less than ” low frequency, very similar the “A” class network below.

For this, the level that chooses to the measurement of industrial noise is level of “A” class noise, use DBA term.

Because sound energy of catoptric a confusion of voices is checked easily,probe captures, set another standard so. This standard asks sound measurement of all a confusion of voices is in “ hollowness undertakes below field condition ” .

Measure regulation of ANSIS51 of aeriform facilities audio to point out: Noise should be in from the machine one Mi Yuan, 1.5 meters of altitude are measured.

Accordingly, we determined a test here probe position and measure the ground is nodded and measure noise with “A” class network.

All manufacturer use these same main provisions to measure noise.

If the machine of level of two same noise moves side by side, the result of noise level will increase 3dBA (double)

For example: In our original formula:

If, we are double level of our sound power arrives 2×10-5

Manufacturer of a compressor states: Noise level assures for + 3dBA is to show its noise level will be of the noise level that its state double or 1/2.

Two aircrew that run with different speed, the likelihood has same noise standard, but sound completely different. The likelihood is harsher than another. Because noise is a basis,this is a number that reachs all frequency addition in spectrum will form DBA.

To measure noise level, the noise that measures each scale zone, try to reach with “A” turns over assess and contrasting answer (DBA) .

These all meaning what:

1, this is meant, because reflex us to cannot find a place for a compressor,be in the room, expectation has and issue same noise standard in hollowness field requirement next.

2, the aircrew that we cannot differ by two solely (with different speed, different drive, different component and different crust) can make guess knowledgeably to noise level. The only method that measures noise is to use a sound to measure equipment.


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8, how do we overcome the apparent difference in noise level?

1, through accurate measure noise level

2, the difference that will assign frequency sensibly through knowing what how form to noise level is and harsh element.

3, know two have identical noise level, differ however the aircrew noise of frequency character is identical to auditive harm, although among them really “ sounds ” is a few lighter.

9, how can we just reduce noise further?

1, all connect in keeping organism are safety, forklift aperture is shut, aircrew is in solid seals the matrix of the ground.

2, carry through conduit into gas and exhaust.

3, reduce reflection noise.

At best of sound and sound measurement of a confusion of voices just is science of a kind of special imprecise. To the discussion of this task the hope can avoid field problem, field amendatory is many of charge and user dissatisfactory.

1, all noise level measures use ANSLS51 level. This is an industry standard. What we should adopt this standard is referenced cite uses noise level. Say briefly, field of hollowness of this standard requirement is measured (without reflection wall and housetop) , the much dot all round aircrew is measured, take average to measured value. Should be in aircrew a meter beyond, 1.5 meters of place on the ground and fundamental level are measured. Any only places measure the A noise level that can have had to cite. As long as average reading can be satisfied or under cite level. In addition, uses measurement is the average of the should broadband zone that measures noise. Should ask or give should when frequency takes an analysis, the reading that a few intermediate frequency take can and measure average watch than noise really normally tall. Point out again, standard place accepts this.

2, did not give in standard structure and applicable public errand

3, the aircrew that finds a place for without true outdoors should be written on ” of “ hollowness field finds a place for. The noise level that chooses regularly actually always wants a few taller, because be mixed from around wall or housetop and the reflex that around equipment distributings.

4, the noise level data that submits possibly is use when measuring should specific compressor measure actually those who get be the same as type compressor to repeat below similar requirement in run the noise level that can be explained to be a model.


When be being measured to any much dots are measured or repeating compressor, have certain error connection. These errors pointed out to assure noise level is opposite the problem of a specific compressor, should measure in total DBA on 3 decibel are added on the value. When giving level of an user noise to assure, obedient above requirement is indispensable.

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2022-10-30T23:53:51-07:00October 2022|Categories: Air Compressor Technology|Tags: , , |