The engine of hermetic piston compressors (piston type compressor), placed in a welded, sealed body, is in a structure where service services such as maintenance and repair cannot be provided. The mechanical system within this body, a piston that moves linearly back and forth within the cylinder, is shown in Figure 2.2. In order to obtain this linear movement, a crank and connecting rod are used to convert the circular motion into linear motion (see Figure 2.3). This type of compressors are produced with a single piston up to 1/2 hp, hermetic compressors are produced with two or more pistons for larger powers.
The application conditions of piston compressors are suitable for refrigerators where the cylinder volume requirement per unit refrigerant cooling capacity is low and the suction/discharge pressure difference is quite high.

There are valves that are activated during suction and discharge due to the linear movement of the piston in the cylinder. These valves are called suction valves and discharge valves, taking the same name due to the position in which they operate. In Picture 2.4 and Picture 2.5, discharge and suction valves are shown on the valve plate. The fact that the piston compressors we mentioned have more mechanically working parts also increases the possibility of malfunction.
In fully closed hermetic type piston compressors, vertical axis crankshaft and engine and horizontal axis cylinder arrangement are frequently used. Due to the structure of fully hermetic piston compressors, the suction vapor passes through the motor windings before being taken into the cylinder or cylinders. This helps both extract some of the heat from the motor windings and evaporate any liquid refrigerant that may have entered the compressor.