According to different compressor designs, there are three types of compressors: hermetic compressor, open type compressor and semi-hermetic compressor. Do you know their differences and advantages? Kotech Compressor will discuss in below.

Hermetic Compressor

What is Hermetic Compressor

A hermetic compressor is a type of compressor that encapsulates the compressor and the motor together in a shell that is welded or brazed, and the two share a main shaft.

(Hermetic compressor)

This design eliminates the shaft seal device, greatly reducing the size and weight of the hermetic compressor, so that only necessary pipes are exposed to the outside, such as suction and exhaust pipes, process pipes and other pipes, power terminals and compressor brackets.

According to the structural characteristics of hermetic compressors, they can be divided into reciprocating piston compressors and rotary compressors. Reciprocating piston hermetic compressors can be divided into connecting rod type, sliding tube type and electromagnetic hermetic compressors.

Rotary hermetic compressors include rotary screw compressors, rotary vane compressors and scroll compressors.

Features of Hermetic Compressor

The hermetic compressor has the advantages of compact structure, good sealing, low noise and smooth operation. The hermetic compressor and the motor are encapsulated in a closed shell together, and the weld at the joint ensures its fully enclosed state.

(Hermetic compressor structure)

This design reduces the possibility of leakage and does not require the use of a shaft seal, thereby improving the reliability and service life of the hermetic compressor.

However, the disadvantage of this design is that it is difficult to perform internal maintenance. Because the hermetic compressor and its motor unit are encapsulated in a sealed shell that cannot be disassembled, once a failure occurs, it needs to be replaced as a whole, which increases the maintenance cost of the equipment.

In summary, the hermetic compressor provides a reliable, efficient and easy-to-integrate solution with its unique design features. However, its difficult maintenance characteristics also put forward higher requirements on the reliability of the equipment.

Since the entire compressor and motor unit are installed in a sealed shell that cannot be disassembled and are not easy to open for internal repairs, special attention should be paid to the stability and fault prevention of the hermetic compressor equipment during design and maintenance.

The hermetic compressor shown in the figure below has its motor and compressor supported by springs. The intake valve 10, the exhaust valve 5 and the drain valve 4 are exposed from the shell for connection to the compressed air system or other processes.

Open Type Compressor

What is Open Type Compressor?

An open type compressor is a type of compressor that can start working immediately without preheating and can quickly compress air, gas or liquid.

Open type compressors generally adopt a reversible design and can be used as both compressors and expanders, and can realize the conversion of compression and expansion working modes. In addition, open type compressors can also be equipped with heat recovery function.

Characteristics of Open Type Compressors

The structural characteristic of an open compressor is that the power input end of its main shaft extends out of the casing and is connected to the motor through a transmission device. This design requires that a shaft seal must be set between the fixed and moving parts of the open compressor to prevent any leakage.

Open type compressors are easy to disassemble and repair. When a part is damaged, it only needs to be disassembled and replaced with a new one. In addition, open type compressors have significant advantages in energy saving, stability, and simple operation, and can meet various production needs.

Open type compressors are widely used in automotive compressors, precision machinery manufacturing, food processing, pharmaceutical and other fields. At the same time, open type compressors also have a variety of installation methods to meet the needs of different production sites.

The figure below shows the structure of an open type compressor. There is a shaft seal 1 at the left end of the crankshaft and an oil pump 10 at the right end. The crankshaft drives the oil pump to supply oil to various lubrication parts.

Semi-hermetic Compressor

What is Semi-hermetic Compressor

Semi-hermetic compressors are not completely sealed, so they are easier to open and easier to repair than closed compressors. However, they usually use more parts than closed compressors, and the noise is greater than that of closed compressors.

(Semi-hermetic compressor)

Features of Semi-hermetic Compressors

The compression chamber and gas inlet and outlet of the semi-hermetic compressor form a semi-closed space, but it is not completely closed like a hermetic compressor. When the gas enters the compression chamber, it is compressed and discharged to the next stage or outside the compressor as the piston or rotor moves.

Semi-hermetic compressors have good sealing performance and can effectively reduce air leakage and pollution. It has the flexibility of an open compressor and the efficiency and safety of a closed compressor.

The main shaft of the semi-hermetic compressor shown in the figure below is a crankshaft 4, which lies horizontally on a pair of sliding main bearings. The left end of the main shaft cantilever supports the motor rotor. Because its motor is a built-in motor, the main shaft does not need to pass through the compressor casing and does not require a shaft seal.

(Semi-hermetic compressor structure)

Troubleshooting of Hermetic Compressors

How to judge whether the hermetic compressor has a fault? Generally, the first thing to judge is the abnormal sound after starting, and the second is to check whether there is oil around the terminal. Common faults of fully enclosed compressors are:

1. The compressor does not start, the reason may be:

a) The compressor is overloaded, the pressure switch, and the overcurrent protector are tripped or damaged.

b) The indoor temperature sensor and the pipe temperature are open or in poor contact, or short-circuited.

c) Check whether the relay is energized, whether the compressor is open or short-circuited, and the compressor capacitor is broken.

2. The compressor has a “thumping” impact sound, the reason may be:

a) The hanging spring material is poor and broken.

b) The hanging spring is not assembled tightly and falls off.

3. The efficiency of the compressor is reduced, the reason may be:

a) The moving parts are worn, making the matching clearance too large.

b) The suction and exhaust valve plates are broken or not closed tightly.

c) The asbestos board of the cylinder gasket is punctured.

4. Oil seepage from the compressor terminals or other welding parts, the reasonmay be:

a) Poor welding of the terminals or cracked glass insulators.

b) False welding of the casing or lead pipe.

5. The compressor motor makes a “humming” sound during operation, the reasonmay be:

Generally, it is caused by serious imbalance of the three phases, one phase of the power supply is missing, and the three phases can be restored.

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