What is Single-Stage, Double-Stage and Multi-Stage Air Compressor?

What is the meaning of single-stage, double-stage and multi-stage air compressor? What is the difference? Which is more energy-efficient? Here let CPMC(Chengdu Pudding Mechatronic Co.) answer these frequently asked questions. With some years working experiences in air compressors industry, CPMC is growing fast to be one of the main exporters via internet.

The team of CPMC has accumulated years of exports experiences through Alibaba / Made-in-China, etc third party network, while with more and more private traffic resources, CPMC dreams to decrease the middle handling fee but improve the efficiency which sets us apart from the most of the Chinese exporters who sell things on third party platform like Alibaba, Made-in-China or Globlesource, Amazon, Ebay, etc. As is known to all that most of these platforms take huge commission, system rental & maintenance annual fee and the annual advertisement fee without which, these platforms like Alibaba never shares any potential traffic to sellers. Thanks to the internet, CPMC can meet the buyers (international wholesalers or retailers or users) directly and offer the MUCH BETTER prices.

It can be said that the single-stage and double-stage air compressors are mainly based on the structure of the main engine, that is, if the compressed air passes through two compressions, they are two-stage, and if it is only one compression, then it is single-stage. Another way is to look at the air end, ie the airend structure. In this way, turbo compressors, centrifugal compressors, and scroll compressors are all single-stage compression air compressors. Generally, the common screw air compressor is also single-stage compression. Now the screw air compressor has two-stage compression, the head adopts an integrated type, and the gas passes through two stages compressions. The piston engine is the most subdivided air compressor, because the piston engine can be designed into single-stage, double-stage (two-stage), three-stage or even multi-stage. Therefore, if you want to get a higher exhaust pressure, the piston-type multi-stage air compressor is the best choice, other models cannot do it.

Speaking of which is more energy-efficient, this is more complicated. Both scroll type and screw type can be made into single-stage, but the energy-saving of double-stage screw. The effect is more obvious. The multi-stage piston engine is the least energy-saving, because the technology is relatively backward. So we should not just talk about single-level and double-level. Which stage is more energy-efficient should be analyzed in combination with different compression types, single-stage and double-stage. Let’s make a comparison with the thermal energy of the air compressor. During the compression process of an air compressor, the power input to the compressor will be converted into high pressurized air. And compressing high-temperature gas requires more energy, therefore, the compressor must have cooling measures.

The lower the temperature rise during the compression process, the more energy-saving the compressor is. The ideal compression process is isothermal compression, that is, the temperature is maintained during the compression process
constant. Piston compressors, turbo compressors and oil-free screw compressors do not have effective cooling methods in the compression process, so the compression process is often divided into multiple stages, and an inter-stage cooler is installed at the outlet of each stage to lower the temperature to close to the ambient temperature. Remove the condensed water, and then send it to the next stage to continue compression. This band-type compression process can limit the maximum temperature within a safe range while keeping the average temperature closer to isothermal. Therefore, for piston compressors, turbo compressors and oil-free screw compressors, multi-stage compression is conducive to energy saving when there is an intercooler.

Oil-injected screw compressors use lubricating oil to absorb heat during compression. Calculated by weight, the lubricating oil sprayed into the main engine per unit time is ten times the air flow rate. Since the lubricating oil has a much larger capacity to absorb heat than air, a large amount of compression heat is lubricated.

The lubricating oil is absorbed to keep the temperature rise during the compression process at a low level. The heat absorbed by the lubricating oil accounts for about 90% of the input power. Inside the fuel injection cooling is the key technology for the rapid development of screw compressors. It can be said that screw compressors can replace piston compressors as the mainstream models in the market rely entirely on unique cooling methods.

The unique cooling method of the oil-injected screw compressor keeps it within the range of ordinary discharge pressure, such as the discharge pressure below 13MPa, and multi-stage compression is not required and cannot be used. First of all, under the condition of giving full play to the advantages of fuel injection internal cooling technology, the compression process. It is not necessary to use multi-stage compression for oil-injected screw compressors. Secondly, there is no inter-stage cooler, more level compression does not have any energy saving effect. Furthermore, if inter-stage cooling is used, the temperature of the gas entering the next stage must be lower than the corresponding pressure. A large amount of water will be analyzed at the dew point temperature under the pressure, and inter-stage oil-water separation and removal components must be installed, otherwise it will contain a lot of water. Once the lubricating oil enters the next stage, it will cause serious deterioration of lubrication and aggravate rotor and bearing wear. The separation of oil and water needs to be kept in a static state for several hours, and the drainage element must have the ability to identify the oil-water interface. So the oil-water separation between stages eliminating the insurmountable obstacles of multi-stage compression screw compressors with inter-stage coolers requires continuous improvement.