Why do air compressors need graded compression?

When the working pressure of the gas is required to be high, single-stage compression is not only uneconomical and sometimes impossible, but multi-stage compression must be used. Multi-stage compression starts with the inhalation of gas and increases the pressure several times to achieve the required working pressure. We will explain in detail why air compressors require hierarchical compression.

The reasons for staged compression of air compressors are as follows:

Save power consumption:

With multi-stage compression, an intercooler can be arranged between the stages, so that the compressed gas is first subjected to isobaric cooling to reduce the temperature before entering the next stage of cylinder. The temperature is reduced and the density is increased, which makes it easy to compress further, which can greatly save power consumption compared with one compression. Therefore, under the same pressure, the area of work done by multi-stage compression is less than that of single-stage compression. The more stages, the more power consumption is saved, the closer it is to isothermal compression.

Improve volume utilization:

Due to manufacturing, installation and operation reasons, the clearance volume in the cylinder is always inevitable, and the clearance volume not only directly reduces the effective volume of the cylinder, but also the residual high-pressure gas in it must also expand to the suction pressure. Only then can the cylinder begin to inhale fresh gas, which is equivalent to further reducing the effective volume of the cylinder.

Reduce exhaust temperature:

The temperature of the discharged gas from the compressor increases with the increase of the compression ratio. The higher the compression ratio, the higher the exhaust temperature, but excessive exhaust temperatures are often not allowed. This is because: in oil-lubricated compressors, high temperature of the lubricating oil will reduce the viscosity and increase wear. When the temperature rises too high, carbon deposits will easily form in the cylinder and on the valves, which will increase wear and sometimes even cause explosions. For various reasons, the exhaust temperature is greatly limited, so multi-stage compression must be used to reduce the exhaust temperature.

Reduce the gas force acting on the piston rod:

On piston compressors, when the compression ratio is high and single-stage compression is used, the cylinder diameter is large, and a higher final gas pressure will act on the larger piston area, and the gas force on the piston will be large. If multi-stage compression is used, the gas force acting on the piston can be greatly reduced, which may make the mechanism lighter and improve mechanical efficiency.

The relevant content will be shared here for everyone. Of course, multi-stage compression does not mean that the more stages, the better, because the more stages, the more complex the air compressor structure, and the size, weight, and cost will increase.