Compressor TypesCompressors come in five different types:
Reciprocating compressors. The motor of this compressor turns a crankshaft, which in turn makes one or more pistons rise and fall. When the piston falls, the refrigerant vapor enters from an intake valve. When the piston rises up, the high-pressure vapor is pushed out through the exhaust valve.
Screw compressors. With this type of unit, the refrigerant vapor is compressed through the use of turning screws. These screws are also known as augers. There are two types of augers, male and female. The male and female augers fit together and turn together. The refrigerant enters through the turning augers, is compressed, and is then released out the other end.
Centrifugal compressors. This compressor uses centrifugal force to compress the refrigerant gas. The gas enters the part of the compressor known as the volute. Inside the volute is a rotating disk with blades called impeller vanes. The disk and its blades look similar to a fan. When this fan spins, it uses centrifugal force to compress the gas and pass it through the system.
Scroll compressors. Refrigerant is compressed by the use of two spiraled scrolls that fit together. One scroll is stationary while the other makes a continuous orbit. The movement of the orbiting scroll causes the refrigerant to be compressed.
Rotary compressors. These compressors work in two ways; both use blades and a rotating rotor. The refrigerant gas enters the compressor and is compressed through the turning of the rotor. In one type of rotary compressor, the blades are stationary as the rotor moves and compresses the gas. In the other type of rotary compressor, the blades move in the opposite direction of the moving rotor.
Design TypesCompressors also come in three basic design types and can be distinguished by the placement of their motor:
Open compressor. This type of compressor works through the use of an outside motor. The motor controls the compressor but is not attached to the compressor. For example, the motor may run the compressor through the use of a belt. The motor turns the belt and thus operates the compressor.
Hermetic. This is the opposite of the open compressor. The motor is directly attached to the compressor for operation. Also, both the compressor and the motor are sealed together within the system. A good way to remember this is to remember the definition of hermetic, which means completely sealed.
Semi-hermetic. This compressor uses elements of both hermetic and open compressors. The compressor and motor are still connected together like the hermetic model, but they are sealed in separate cases.
How The Reciprocating Compressor WorksRemember that the compressor is used to take vapor from the evaporator and condense it into a smaller volume.
1. The vapor enters the reciprocating compressor through the suction chamber, which is located in the compressor head. This part of the compressor is divided into two parts. One side is for discharge pressure and the other side is for suction pressure.
2. The vapor then passes through the valve plate, which serves as a division between the high- and low-side pressure and is located under the compressor head and above the piston.
3. Next, the vapor will pass through the suction valve reed. This is attached directly beneath the valve plate and directly above the piston. When the piston strikes down, the low-pressure gas is brought into the compressor cylinder. As the piston charges upward, the gas becomes trapped in the cylinder and is compressed into a lighter volume.
4. When the pressure in the compressor cylinder gets high enough, the discharge valve reed opens. This reed is much like the suction valve reed, but it’s located at the opening of the discharge chamber. Above the discharge valve reed is a restrainer. This device stops the discharge valve reed from opening too far and can also protect against liquid refrigerant that may be in the compressor.
Publication date: 11/19/2001