Common compressor structures on the market include piston compressors, twin-screw compressors, single-screw compressors, scroll compressors, vane compressors, etc. The three criteria for judging the advantages and disadvantages of compressor structures are: the smallest internal gap; the lowest manufacturing cost to obtain a reasonable gap; the gap does not change over time.
In other words, the three criteria for judging the advantages and disadvantages of compressor structures:
1. Minimum internal leakage;
2. The lowest manufacturing cost to control leakage within a reasonable range;
3. The leakage amount does not change over time.
1. Minimum internal gap. There is generally a gap inside the compressor head, and there must be leakage if there is a gap. When the compressor is in a stationary state, the leakage from the exhaust side to the intake side under a certain pressure is a constant, and basically does not change with the speed or exhaust volume. The change in speed or exhaust volume only changes the relative leakage of the head, that is, the ratio of leakage to intake volume. Gas leakage from the exhaust side to the intake side seriously affects the performance of the compressor. The reflux gas not only heats the intake air, making it more difficult to compress the gas, but also repeatedly compresses the reflux gas, constantly consuming a part of the motor power. The whistling sound caused by the gas passing through the gap is the main component of the head noise. Increasing the head speed is the main means to reduce the relative leakage, but increasing the speed will increase friction and wear, shorten the bearing life, and reduce the reliability of the machine. The length of the gap between different models varies greatly, and this difference seriously affects the efficiency of the machine.
2. The manufacturing cost of obtaining a reasonable gap is the lowest. The working chamber of the piston compressor is a simple cylinder and a circular hole. A reasonable gap can be obtained with ordinary processing equipment, so the cost of obtaining a reasonable gap is very low. Since general equipment is used, the investment risk is also relatively small. The screw compressor has a complex curved surface, and expensive high-precision special equipment and measuring instruments must be used to ensure the processing quality; the equipment also has strict requirements on the temperature and humidity of the plant; due to the high cost of special tools, in order to reduce the processing cost, it is often necessary to use the tool life in one clamping, which is very likely to cause a huge inventory of parts and a backlog of funds. The same is true for single screw and vortex machines. Among rotary compressors, only the vane compressor can obtain a reasonable clearance with ordinary processing equipment.
3. The clearance does not change with time. The machine will wear. Due to wear, the clearance increases, resulting in a decrease in efficiency after long-term operation of the compressor. The piston ring cut of the piston compressor will increase after long-term operation, resulting in a decrease in efficiency. The star wheel of the single-screw compressor will increase the clearance and decrease the efficiency after wear. After the thrust bearing of the twin-screw compressor is worn, the end face clearance at the exhaust end increases, resulting in increased internal leakage and decreased efficiency. Although the vane of the vane compressor is also wearing, it can automatically compensate and will not increase the clearance due to wear, so the efficiency of the vane compressor can remain unchanged for a long time. Automatic and immediate compensation for wear is a necessary condition to keep the leakage unchanged over time. Among all known compressor structures, only the vane compressor has this feature.