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General Interest Industry

Open, Hermetic and Semi-Hermetic Compressors

Hermetic compressors are frequently found in air conditioning and refrigeration applications. This article explores the attributes of this type of compressor.
What does Hermetic Mean?
In order to understand what a hermetic compressor is the first thing to do is understand what hermetic means. Something that is hermetic has been made ‘airtight by fusion or sealing’. In the case of compressors, this is usually done by welding the shell of the device together.
Hermetic Compressors
In a hermetic compressor, the components are isolated from the outside world. The compressor – and often the motor – is integrated within the refrigerant system. These units present the disadvantage that they can be difficult to service.
Accessing a compressor for repairs when it is sealed within a welded system is obviously not practical in the field without serious equipment. This means that often times an entire compressor system needs to be removed and replaced in case of failure of one of the components.
Semi Hermetic Compressors
An alternative to the hermetic compressor is the semi-hermetic compressor. These are similar in design but have one significant difference. In semi hermetic compressors the casing for the unit is not welded, but is instead sealed gasketed covers.
The advantages for servicing of this design are obvious. When a component breaks, the unit can be opened up and individual pieces replaced; this is preferable to having to replace the whole unit.
Open Compressors
The advantage of hermetic and semi-hermetic compressor systems is that there is no way for refrigerant gases to escape or leak from the system – they are airtight. The alternate technology of open compressors however can leak. This is because they rely rubber or leather seals to keep the units pressurized; and if not kept lubricated these systems can leak refrigerants over time.
Unlike hermetic systems – which can sit unused for long periods without losing gasses – an open system requires regular use and maintenance to ensure proper functionality.
Many mass produced consumer goods make use of hermitic compressors. They make financial sense where the cost of repairing a unit is larger than simple replacement. Since they require minimal maintenance, they are great choices for residential cooling applications.
Open compressors are a more popular technology for applications utilizing non-electric power. Vehicle cooling systems using a gasoline engine are a good match for this type of technology, but they do require periodic maintenance.