Recognition: "Piston Compressors"

The work of the piston compressor is accomplished by the continuous change of the working volume constituted by the cylinder, the gas valve, and the piston reciprocating in the cylinder. If the volume loss and energy loss in the actual operation of the piston compressor are not taken into consideration (ie, the ideal working process), the work performed by the piston compressor per revolution may be divided into suction, compression and compression processes, and exhaust. process.

Piston compressors classification

According to the classification of working fluids used, there are generally two kinds of ammonia compressors and Freon compressors.

Classified by compression stages, there are single-stage compression and two-stage compression. A single-stage compressor means that the refrigerant vapor only compresses once during compression from low pressure to high pressure. In the so-called two-stage compressor, the refrigerant vapor in the compression process is continuously compressed twice from low pressure to high pressure.

According to the mode of action, there are single-acting compressors and double-acting compressors. The refrigerant vapor is only compressed on one side of the piston, the piston makes a round trip, and the suction and exhaust are once. The double-acting compressor refrigerant vapor is compressed in the cylinders on both sides of the piston. The piston reciprocates one stroke and sucks and exhausts twice. Therefore, the same size of the cylinder, double-acting compressor suction than single-acting. However, due to the complex structure of double-acting compressors, single-acting compressors are currently used.

According to the classification of the movement of refrigerant vapor in the cylinder, there are a direct current type and a countercurrent type. The so-called direct current type refers to the movement of the refrigerant vapor in the same direction from inhalation to exhaust. In the counter-flow type, the direction of movement of the refrigerant vapor in intake and exhaust is reversed. From the theoretical analysis point of view, compared to the direct flow type and the counter flow type, because the vapor temperature and specific volume change in the cylinder is less, so the direct current type performance is better. However, since the inlet valve of the direct-flow type compressor needs to be installed on the piston, the length and weight of the piston are relatively increased, and thus the power consumption is increased and the maintenance is also troublesome. Therefore, most of the current production compressors use the counter-flow type.

According to the position of the cylinder center line, there are vertical compressors, horizontal compressors, V-type, W-type and S-type compressors. The vertical centerline of the vertical compressor cylinder is horizontal and the horizontal centerline of the horizontal compressor cylinder is horizontal. V-type, W-type, and S-type are high-speed, multi-cylinder, modern compressors. The speed is generally 960 to 1440 revolutions per minute, and the number of cylinders is mostly 2, 4, 6, and 8. Among them, the letters indicate the cylinders. Arrangement form.

Piston refrigeration compressors, according to their structural characteristics, can also be divided into open, semi-closed and fully enclosed three. Although the structures are different, there are many similarities between them, but their structural characteristics are different.

The structure of the open type refrigerating compressor is characterized in that the power input shaft of the compressor extends out of the body and is connected with the motor through a coupling or a pulley, and is sealed at the protruding position with a shaft sealing device. At present, ammonia compressors and Freon compressors with larger capacities all adopt this type of structure.

The structural characteristics of the semi-hermetic refrigerating compressor are: the compressor and the motor share a single spindle and are assembled together in the same casing. However, the casing is a detachable type, and various working holes are opened and sealed with a cover plate.

The structural features of a totally enclosed refrigeration compressor are that the compressor shares a single spindle with its drive motor, and the two are assembled in a welded, molded, sealed housing. This type of compressor has a compact structure, good sealing, easy to use, small vibration, low noise, and is widely used in small-scale automated refrigeration and air conditioning devices.

Piston compressor working principle

The work of the piston compressor is accomplished by the continuous change of the working volume constituted by the cylinder, the gas valve, and the piston reciprocating in the cylinder. If the volume loss and energy loss in the actual operation of the piston compressor are not taken into consideration (ie, the ideal working process), the work performed by the piston compressor per revolution may be divided into suction, compression and compression processes, and exhaust. process.

Compression process

The piston moves upward from the bottom dead center, the suction and exhaust valves are closed, and the gas is compressed in the closed cylinder. As the cylinder volume is gradually reduced, the pressure and temperature gradually increase until the gas pressure in the cylinder is equal to the exhaust pressure. The compression process is generally viewed as an isentropic process.

Exhaust process

As the piston continues to move upwards, causing the gas pressure in the cylinder to exceed the discharge pressure, the exhaust valve opens and the gas in the cylinder is forced out of the cylinder by the piston to enter the exhaust pipe until the piston moves to top dead center. At this point, due to the exhaust valve spring force and the gravity of the valve plate itself, the exhaust valve closes the exhaust.

At this point, the compressor completes a working cycle consisting of three processes of suction, compression, and exhaust. After this, the piston moves downward again, repeating the above three processes, so that the cycle is repeated. This is the ideal working process and principle of a piston refrigeration compressor.