Working principle diagram of piston air compressor shown in Figure 1

1 – exhaust valve 2 – cylinder 3 – piston 4 – piston rod

Figure 1

Figure 1

5 – slider 6 – connecting rod 7 – crank 8 – suction valve

9 – valve spring

When the reciprocating piston in the cylinder moves to the right, the pressure in the left chamber of the piston in the cylinder is lower than the atmospheric pressure PA, the suction valve is opened, and the outside air is sucked into the cylinder. This process is called compression process. When the pressure in the cylinder is higher than the pressure P in the output air pipe, the exhaust valve opens. Compressed air is sent to the gas transmission pipe. This process is called exhaust process. The reciprocating motion of the piston is formed by the crank slider mechanism driven by the motor. The rotary motion of the crank is converted into sliding – the reciprocating motion of the piston.

The compressor with this structure always has residual volume at the end of the exhaust process. At the next suction, the compressed air in the remaining volume will expand, so as to reduce the amount of inhaled air, reduce the efficiency and increase the compression work. Due to the existence of residual volume, the temperature increases sharply when the compression ratio increases. Therefore, when the output pressure is high, staged compression shall be adopted. Staged compression can reduce the exhaust temperature, save compression work, improve volumetric efficiency and increase the exhaust volume of compressed gas.

Figure 1 shows a single-stage piston air compressor, which is commonly used for 0 3 — 0 . 7 MPa pressure range system. If the pressure of single-stage piston air compressor exceeds 0 6Mpa, various performance indexes will drop sharply, so multistage compression is often used to improve the output pressure. In order to improve efficiency and reduce air temperature, intermediate cooling is required. For the piston air compressor equipment with two-stage compression, the pressure of the air increases from P1 to P2 after passing through the low-pressure cylinder, and the temperature increases from TL to T2; Then it flows into the intercooler, releases heat to the cooling water under constant pressure, and the temperature drops to TL; Then it is compressed to the required pressure P 3 through the high-pressure cylinder. The air temperatures TL and T2 entering the low-pressure cylinder and high-pressure cylinder are located on the same isotherm 12 ′ 3 ‘, and the two compression processes 12 and 2 ′ 3 deviate from the isotherm not far. The single-stage compression process of the same compression ratio p 3 / P 1 is 123 “, which is much farther from the isotherm 12 ′ 3 ′ than the two-stage compression, that is, the temperature is much higher. The single-stage compression consumption work is equivalent to the area 613 ″ 46, the two-stage compression consumption work is equivalent to the sum of the areas 61256 and 52 ′ 345, and the saved work is equivalent to 2 ′ 23 ″ 32 ‘. It can be seen that staged compression can reduce exhaust temperature, save compression work and improve efficiency.

Piston air compressors have many structural forms. According to the configuration mode of cylinder, it can be divided into vertical type, horizontal type, angular type, symmetrical balance type and opposed type. According to the compression series, it can be divided into single-stage type, double-stage type and multi-stage type. According to the setting mode, it can be divided into mobile type and fixed type. According to the control mode, it can be divided into unloading type and pressure switch type. Among them, the unloading control mode means that when the pressure in the air storage tank reaches the set value, the air compressor does not stop running, but carries out uncompressed operation by opening the safety valve. This idling state is called unloading operation. The pressure switch control mode means that when the pressure in the air storage tank reaches the set value, the air compressor will automatically stop running.