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Basic Knowledge


Time: 2020-08-25

Summary:This article introduces the function of components of oil injection screw air compressor, analyzes the working principle of components and points for attention in maintenance, and analyzes and removes individual faults.

1.lubricating oil

Lubricating oil has lubrication, cooling and sealing functions.

  ·Note that the lack of oil level of lubricating oil will cause the unit to accumulate carbon at high temperature, and will also cause accelerated wear and tear of operating parts, which will damage the service life of the unit
  ·Condensate water is prevented from occurring in the lubricating oil. It is advisable to keep the operating oil temperature around 90℃ and resolutely prevent the operating oil temperature below 65℃

Lubricating oil composition: base oil + additive

Additives have the following functions: anti-foam, anti-oxidation, anti-corrosion, anti-solidification, anti-wear, descaling (corrosion) viscosity is more stable (especially at high temperature) and other lubricants can be used for up to one year, the lubricating oil will deteriorate for a long time.

2.Screw air compressor components function


The function of Air filter

The most important task is to prevent the dust and other impurities in the air into the air compressor system filtration accuracy :0.001mm particles filter 98%, 0.002mm particles filter 99.5%, more than 0.003mm particles filter 99.9% .

The function of Oil filter

Remove all impurities and dust that cause wear from the lubricating oil, but do not separate the special additives added .
Filter paper precision :0.008mm particles filter out 50%,0.010mm particles filter out 99% fake filter paper has not been tested by heating oil, only fewer folds, greatly reducing the filtration area, and the fold spacing is not uniform .
If the air in the inlet contains much dust, the filter paper will be severely blocked after a period of use, and the filter will prevent the flow of lubricating oil into the oil filter. If the differential pressure of lubricating oil is too large (cold starting or filter blocking), the oil circuit will be short of oil, and the temperature of lubricating oil will rise, which will damage the rotor.

3.Working principle of oil and gas separator

The function of oil and gas separator

It is mainly to separate the compressor lubricating oil from the mixture of oil and gas and continue to remove the lubricating oil particles in the compressed air .
After entering the oil and gas barrel (consisting of the minimum pressure valve and safety valve of the oil and gas separator and the container housing), the oil and gas mixture passes through three kinds of separation: centrifugal separation, gravity separation (oil ratio, gas weight) and fiber separation .
Separation process: the mixture of oil and gas along the line tangent to the outer wall of oil and gas separator into the barrels of oil and gas, 80% ~ 90% of the oil separated from the mixture of oil and gas (centrifugal separation), the rest (10% ~ 20%) of oil viscosity in the outer wall surface oil and gas separator separation (gravity separation), a small amount of oil into the oil and gas separator inside (fiber separation), the return pipe pressure back to screw host cavity .

Gaskets for oil and gas separators are electrically conductive

As the air oil passes through the glass fiber, static electricity will be generated between the two separation layers. If the two metal layers are covered with static electricity, there will be a dangerous situation of electrostatic discharge accompanied by electric spark, which may cause an explosion of the oil-gas separator .
Good oil and gas separator accessories ensure the conduction between the separator core and the oil and gas barrel shell. The metal components of the air compressor have good electrical conductivity, which can ensure that all the static electricity can be discharged in time and prevent the generation of electric sparks.

Adaptability of oil and gas separator to differential pressure

Oil and gas separator is designed to carry the differential is limited, if separator filter more than the maximum value, the oil and gas separator are likely to rupture, oil from compressed air can not be separated, it will affect the air compressor or cause separator core is completely broken, and oil and gas separator of high pressure drop also is likely to cause fire in the separator .
Causes of high pressure difference may have the following 4 points: due to dirt blocking oil separator, air countercurrent, internal pressure fluctuation is large, fake oil and gas separator core .

The oil and gas separator metal is normally electroplated and usually not corroded

According to the surrounding environment (temperature and humidity) and the working condition of the compressor, condensed water may be formed inside the oil and gas separator. If the oil and gas separator is not electroplated, a corrosion layer will be formed. This corrosion layer will damage the antioxidant of the compressor oil and significantly reduce its service life and oil flash point

Measures to ensure the service life of oil and gas separator

Accumulated dust and residual oil air pollutants or wear will reduce the service life of the oil and gas separator .
A.The air filter and oil filter can be changed timely and the oil change time can be observed to limit the dust into the compressor oil
B.Use the correct lubricant which is resistant to aging and is not affected by water

4.Screw air compressor a few points to note

Screw air compressor rotor must not be reversed

The rotor is the core part of the screw air compressor. The Yin and Yang screw surface does not touch, and the Yang and Yang screw has a gap of 0.02~0.04mm. The oil film plays a protective and sealing role .
If the rotor inversion, cannot build up pressure in the pump head, the pump head screw no lubricating oil, cannot make oil circulation, the pump head instantaneous heat accumulation, produce high temperature, make the pump head screw and shell deformation, Yin Yang, screw occlusion, holding in death of rotor end and the end cover due to the high temperature stick together, causing the rotor end surface wear seriously even parts defect, gear box and rotor damage scrap .
Check the rotation direction: the phase sequence of the screw air compressor motor will change because of the change of the factory's incoming line phase sequence or the change of the screw air compressor's incoming line power, etc. Most air compressors have phase sequence protection, but to be on the safe side, the following inspection should be made before the air compressor runs .
  ·Hold the cooling fan contactor by hand to see if the wind direction is correct
  ·If the fan power line has been moved, manually inching the main motor for a moment, to see if the motor coupling rotation direction is correct

Screw air compressor rotor can not carbon deposition

Carbon deposit reasons

Use inferior lubricant which is not the genuine oil of the original manufacturer
  ·Use false or damaged air filters
  ·Run at high temperature for a long time
  ·Less lubricating oil
  ·When changing lubricating oil, the old lubricating oil is not cleaned or the old and new lubricating oil is mixed
  ·Different types of lubricants are used together

Check the method of rotor carbon deposition
  ·Remove the inlet valve and observe whether there is carbon deposition on the inner wall of the pump head
  ·Observe and analyze whether the lubricating oil contains carbon deposit from the surface of the oil filter and the inner wall of the lubricating oil pipeline

Check the pump head as required
Screw air compressor pump head shell non-professional personnel are not allowed to remove, the pump head if carbon accumulation only professional technical personnel can maintain the screw air compressor pump head Yin Yang screw clearance is very small, pay attention to the maintenance of the pump head can not enter any impurities .

Add motor bearing grease regularly
Add with special oil gun, specific steps:
  ·Opposite the nozzle, open the vent hole
  ·The nozzle of the oil gun should be matched with the motor
  ·Lubricating grease can be divided into high speed motor grease and low speed motor grease. The two cannot be mixed, otherwise there will be a chemical reaction between them
  ·The oil content of the oil gun is 0.9g after each pressure, and 20g is added each time, which needs to be pressed several times
  ·If less grease is added, the grease is not lubricated on the oil line; If added too much, bearing heat, grease into liquid, affect the lubrication quality of the bearing
  ·The air compressor is added every 2000h

Replace main motor coupling
The coupling must be replaced under the following circumstances:
  ·The surface of the coupling is cracked
  ·Charred surface of coupling
  ·Coupling glue grease is broken

5.Fault analysis and elimination of screw air compressor

A 40m³/min screw air compressor caught fire during operation in a company 

Screw in the compression process of high temperature, through the lubricating oil injection, the heat away, and then reduce the temperature of the head if there is no oil in the screw, instantly hold the head of the injection point each head design is different, so all kinds of screw air compressor plant oil products are not the same.

The screw air compressor in operation catches fire and the machine is scrapped for the following reasons:

The flash point of the lubricating oil is about 230, and the ignition point is about 320 using inferior lubricating oil. After the lubricating oil spray atomization, the flash ignition point is reduced
  ·The use of poor quality wear parts, resulting in air compressor oil road gas road blocked, gas road oil parts temperature is too high for a long time, easy to produce carbon deposition
  ·Gaskets of the oil and gas separator are not conductive, and the static electricity generated by the oil and gas separator cannot be exported
  ·There is an open fire in the machine and a leak injection point in the oil system
  ·Flammable gas is drawn in at the intake
  ·Residual oil is not discharged, and the oil mixture deteriorates
Through relevant experts, engineers and technicians jointly confirmed that the machine was maintained with inferior lubricating oil and inferior vulnerable parts, and the static electricity generated by the oil-gas separator could not be exported, resulting in the machine being scrapped on fire.

The screw air compressor shakes violently when unloading and has the fault of pouring lampblack

During operation, the unloading time head of the screw air compressor shakes, and the air filter alarms every 2 months. The air filter is not effective to clean the air with high pressure wind, and the air filter is removed. There is lampblack generated in the suction pipe, and the lampblack and dust will mix closely to kill the air filter.
After disconnecting the air inlet valve and finding that the seal of the air inlet valve is damaged and replacing the repair package of the air inlet valve, the screw air compressor operates normally.

Screw air compressor runs for 30min or so, and replace with a new V-belt fracture fault

Screw compressor of the pre-tightening force needed for the V belt are set in before they leave the factory, the replacement of damaged the operator in order to save Labour when the ease of installation of V belt V belt, loosen the lock nut, reduce tension after the replacement of V belt automatic tensioning system did not make the lock nut back to its original position (the corresponding color marker), fever due to V belt loose wear, caused the new change of 6 V belt fracture failure again.


Screw air compressor operators maintenance should always pay attention to the matters needing attention in the maintenance, understand the function of the main parts of the air compressor is very necessary equipment management and management department personnel to purchase the original manufacturers wear parts, to prevent the occurrence of inferior lubricating oil inferior parts, prevent the occurrence of unnecessary fault events
If you want to know more about air compressor, please contact Elang professional team.