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Lubrication Mechanism and Accident Prevention of Different Types of Compressors

  • 2021-12-08

Lubrication Mechanism and Accident Prevention of Different Types of Compressors 

1. Lubrication of air compressor

     Compressors can be divided into the following three categories according to the lubrication method: oil-free compressors, where the compressed air does not come into contact with lubricating oil, such as power compressors, labyrinth compressors, diaphragm compressors or compressors with oil-free lubricated piston rings; For oil-lubricated compressors, the moving parts in the compression chamber are lubricated with oil. The lubricating oil is supplied by a special oil injector or by other parts of the compressor, such as a single-acting reciprocating piston compressor without crosshead; an oil-injected rotary compressor, a large amount The lubricating oil is sprayed into the compression chamber. The lubricating oil not only lubricates the moving parts, but also helps to seal and absorb the heat of compression. Lubrication methods include oil injection lubrication, splash lubrication, etc.

   1. Oil-free rotary and reciprocating compressors

  Almost all oil-free compressors have oil-lubricated bearings, driving mechanisms or gear transmissions. A stuffing box or other device is used to separate the lubricated part of the compressor from the compressed air part to prevent air and oil from contacting each other.

  In the lubrication part of the machine, the risk of insufficient lubrication that causes wear and then damage is usually small. Some high-speed compressors are a dangerous period for lubrication when starting and stopping. Therefore, these machines are always equipped with safety devices to control the oil pressure during startup and shutdown operations. Some machines use a separate oil pump, that is, before the compressor is started, the oil pump is turned on to establish the oil pressure.

In some compressors, the seal between the lubricated part and the oil-free part of the machine is prone to a certain degree of wear, resulting in the leakage of lubricating oil into the compression chamber. This leakage will not only make the compressor unsuitable for use, but also The formation of carbon deposits in the pressure system.

   2. Oil-lubricated compressor

   The correct selection and use of compressor lubricants is not only to meet the normal lubrication requirements, but also to eliminate carbon deposits and at least reduce the formation of carbon deposits in the exhaust system. The grade and brand of lubricating oil usually used should be recommended by the compressor manufacturer.

  The main cause of fire in oil-lubricated compressors is the formation of carbon deposits, so the latest development direction is to directly produce lubricating oil that is not easy to deteriorate and not easy to form deposits. The oxidation resistance of the oil and the time it is exposed to the hot air of the exhaust system are two very important points. The oil with good oxidation resistance depends on the choice of base oil with anti-oxidation effect or the addition of antioxidants that are stable at the compressor discharge temperature. The oil exposure time depends on the structure of the pressure system and the viscosity of the oil. The lower the viscosity of the oil, the easier it is to move along the pipe, but it is also prone to vaporization. Therefore, it is important to use oil with proper distillation characteristics. If the distillation range of an oil is too wide, the light oil part of the oil will be vaporized, and the heavier part will remain because of its higher viscosity and stay in the hot zone for a longer time.

  3. Oil-injected rotary compressor

  Oil-injected rotary compressors generally have no problem of carbon deposits due to their low exhaust temperature. However, as circulating oil, they should have a good anti-oxidation effect to ensure a certain lifespan. For oil-injected rotary compressors, special oil or circulating oil with good anti-emulsification should be used. Antioxidants should have low enough volatility at normal compressor temperatures to keep the oil until the time of oil change.

   4. Use of lubricating oil

   Generally, the brand and grade of lubricant recommended by the compressor manufacturer should be used. If other lubricants are used, the compressor manufacturer should be discussed. The oxidation reaction of oil will form acetaldehyde, which has a low auto-ignition temperature, and is therefore potentially dangerous.

   The high temperature safety switch of the oil-injected rotary compressor should be set not higher than the maximum discharge temperature + 10. The industry generally believes that the regulation should not exceed 120. For oil-lubricated compressors operating in the open air or in a non-hot machine room, the calculated viscosity of the lubricating oil should not exceed 2000mm2/s at the lowest possible ambient temperature, and the freezing point should be about 5°C lower than the lowest ambient temperature.

   If the ambient temperature is particularly high, lubricating oil with a high viscosity grade must be used. Special attention should be paid to ensure that the lubricating oil is non-toxic if air may be inhaled. The oil supplier shall provide information to enable users to assess any health hazards related to the intended use of compressed air. The limit value of oil mist in the air is usually set at 5mg/m3.

  It is advisable to choose the lubricating oil that meets the lubrication requirements and has the lowest viscosity. The lubricating oil must be suitable for starting at the lowest ambient temperature and running at the highest ambient temperature. Under special circumstances, lubricating oils of different viscosity grades can be used in different seasons of the year.

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