What is the Difference between a Hermetic Compressor and a Semi-hermetic Compressor?

2022/10/27 ClassificationIndustry News 213

What is the Difference between a Hermetic Compressor and a Semi-hermetic Compressor?

At present, the main market is semi-hermetic piston compressors, which are generally driven by four-pole motors, and their rated power is generally between 60 and 600KW. The number of cylinders is 2–8, up to 12.

The fully enclosed compressor and the motor used share a main shaft and are installed in the casing, so the shaft sealing device is not required to reduce the possibility of leakage.

Advantages: The compressor and the motor are installed in a shell welded or brazed, and share a main shaft, which not only cancels the shaft sealing device, but also greatly reduces and reduces the size and weight of the entire compressor. Only the suction and exhaust pipes, process pipes and other necessary pipes (such as spray pipes), input power terminals and compressor brackets are welded on the exterior of the casing.

The disadvantage is that it is not easy to open and repair: because the entire compressor motor unit is installed in a sealed casing that cannot be disassembled, it is not easy to open for internal repairs, so this type of compressor is required to have high reliability and long life. The installation requirements of the system are also high, and this fully enclosed structure is generally used in small-capacity refrigeration compressors produced in large quantities.

Semi-hermetic compressors mostly use the overall structure of the cylinder block and crankcase, and the motor shell is often an extension of the crankcase of the cylinder block to reduce the connection surface and ensure the concentricity between the compressor-level motors; For the convenience of casting and processing, it is made separable, and is connected by flanges at the joints. The crankcase and the motor room are connected by holes to facilitate the return of lubricating oil.

The main shaft of the semi-hermetic compressor is in the form of a crankshaft or an eccentric shaft; some of the built-in motors are cooled by air or water, and some are used to inhale low-temperature working fluid vapor. For semi-hermetic compressors in the small power range, centrifugal oil supply is often used for lubrication. This kind of lubrication method has a simple structure, but when the compressor power increases and the oil supply is insufficient, the pressure lubrication method is changed.

advantages:

1. Can adapt to a wider pressure range and refrigeration capacity requirements;

2. The thermal efficiency is high, and the unit power consumption is less, especially the existence of the gas valve makes the deviation from the design condition more obvious;

3. The material requirements are low, and ordinary steel materials are often used, which is easier to process and relatively cheap;

4. The technology is relatively mature, and rich experience has been accumulated in production and use;

5. The installation system is relatively simple.

The above-mentioned advantages of the semi-hermetic piston compressor make it the most widely used type of refrigerators with a larger production volume in various refrigeration and air-conditioning devices, especially in the range of medium and small cooling capacity. At the same time, the semi-hermetic piston compressor not only maintains the advantages of easy disassembly and repair of the open compressor, but also cancels the shaft sealing device, which improves the sealing condition. The unit is more compact and has low noise. When the working fluid cools the motor, it is beneficial to the miniaturization and weight reduction of the machine. At present, semi-hermetic piston refrigeration compressors using R22 for medium and low temperature are widely used in cold storage, refrigerated transportation, freezing processing, display cabinets and kitchen refrigerators.

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