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A hermetic compressor is a compressor unit that, unlike others, is completely sealed. Most compressors must have the compressor and motor connected via a belt to properly function, but a hermetic compressor conjoins the two units. One problem with this type of unit is that it cannot be opened; if there is a problem, then the compressor normally has to be replaced. The entire unit is sealed, so there is almost no way for gas to leak out unless the shielding is cracked. Lubricants are not required to keep this compressor working, and it typically can be stored for months or years without starting problems occurring.
The majority of compressors are really made of two pieces: the motor and the compressor. A belt usually is required so the two can be connected and the motor can run the compressor. With a hermetic compressor, both pieces are sealed within a steel shielding. This normally makes the compressor smaller, and operators rarely need to be concerned with the motor not driving the compressor.
Gas is often used to power a hermetic compressor, and this may be a problem with other compressors. If seals are not maintained, then the gas can leak out and damage these compressors. The shielding on a hermetic compressor keeps the gas locked inside the unit. At the same time, if there is any gas leakage, this can cause massive internal damage, which eventually makes the compressor unusable.
Most compressors need lubricants to keep the rubber, leather or belt materials soft and pliable; otherwise, the materials dry out and become unusable. When these compressors are stored for a long time, the lubricant dissolves and the belt will need to be replaced before these compressors can be used again. The hermetic compressor does not have a belt, and the compressor is not open to the world, so there is no need for lubricants. This means a hermetic compressor can be stored for months or years and can normally be started back up without any problems.
While the hermetic sealing offers many benefits, there is one large disadvantage. A regular compressor can be opened and repaired if there are any problems. Opening a hermetic compressor cannot be done without severely damaging the unit. If opened, then the steel shielding has to be replaced by hermetically sealing a new shield back to the compressor. Opening and repairing this type of compressor is often expensive and difficult, so it is commonly thrown away and replaced with a new compressor.