In a vapor-compression units most important element is in the compressor. Also being the most important part in the the V.C. Unit it also the most expensive part. There are different types of compressors. The type that is use in refrigeration unit are in two groups. The groups are; positive displacement and rotor-dynamic.

The positive displacement type of compressor works by trapping the refrigerant vapor into an enclosed space and then reducing the volume. By doing this the pressure rises and the volume gets reduced because there is a steady amount of refrigerant that is being trapped each time. Two examples of a positive displacement compressor is a reciprocating or a piston compressor. They are the most commonly used PDC that are used. It can be found in ranges from very little horsepower to very high horse power. The reciprocating compressors work in kind of the same manner as does as a internal combustion engine. Except it works in reverse they have cylinders, pistons, crankshafts, valves and housing blocks.

The rotor-dynamic type of compressor uses the pressure to rise the refrigerant that is provided by rising the kinetic energy to a steadily flowing stream. It does this with a rotating mechanical element and then converting the refrigerant into pressure as it flows through a forked passage. The rotor -dynamic compressors have less vibration because they have a more steady flow. There are to different types of RDC. The first is radial flow. This type of compressor is used in large sized refrigeration units and in air conditioning systems. The rotor -dynamic compressors have less vibration because they have a more steady flow. The second is axial flow. This type is commonly used in gas liquefaction appliance.

Depending on the type of alignment of the motor or external dive it can either be an open, hermetic which is sealed,or a semi-hermetic which is partially closed. The open type is more efficient and it has better flexibility, and also better compressor cooling and service capabilities. Due to the rod having to extend through the seal, you can not completely stop the leaking of refrigerant.

With the hermetic type it is surrounded by a box so you do not get any leaking. It works best in units that capillary tubes for expansion mechanism and are critically charged systems. They do not leak but you can not service this type. Also it is not very flexible It is very hard to change the speed of the cooling. This kind is more commonly used in small refrigerators, air conditioners and water coolers. This type is what is used in your home.

The last is the semi-hermetic. This kind works the same as a hermetic kind except for the box around the equipment so it is easier to maintain. Because it is easier to get to.

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