Single Stage vs. Two Stage Compression of Piston Air Compressor
In the actual use of some low pressure and medium pressure piston type portable air compressor, the two stage compression is often used. The intermediate cooler is set. After the cooling of high temperature air discharged from single stage compression, it is then inhaled into two stage cylinder for two stage compression so as to reach the required pressure. Adopt two stage compression, because if use single stage compression to obtain higher air pressure, the pressure ratio (the ratio of the exhaust pressure and suction pressure) is too large, so that the compression process, and air compressor will have the following defects.
- The large amount of heat generated after the pressure ratio is raised cannot be eliminated in time due to the limitation of cooling conditions and cooling efficiency, so that the variable compression line is far away from the isothermal compression line and near the adiabatic compression line, which will greatly increase the power consumption.
- If the temperature of the compressed air is too high, due to heat exchange, the lubricating oil will lose its original performance, such as lower viscosity, resulting in poor lubrication and failure of the compressor. In severe cases, the lubricating oil may also be burned.
- The pressure ratio of air compressor is too high. The high pressure air remaining in the clearance volume will increase the cylinder volume when the suction expands. It will reduce the amount of air suction and reduce the volume flow.
- In order to adapt to the high pressure ratio generated by the load, the size of the piston and the crankshaft connecting rod mechanism of the air compressor must be increased accordingly, which will increase the manufacturing difficulty and increase the cost.
However, it can reach the requirement for high pressure by using two stage compression. It has lower power consumption than single stage compression. The temperature of the compressed air which is cooled by the intercooler can be greatly reduced. Some water can precipitated, which ensures good lubrication of the piston air compressor and provides lower cold air for the next compression. Meanwhile, because the area of two stage piston is smaller than the area single stage compressor piston, the force on piston can be declined and the force acting on the crankshaft link mechanism can be decreased, which can improve the safety of the operation correspondingly.