Hermetic and Semi-Hermetic


There are compressors in the market for various applications with different shapes, functions and characteristics.

One of the ways in which they differ relates to their operating principle. In this case, they can be divided into five types:

  • Reciprocating;
  • Rotary
  • Scroll;
  • Screw;
  • Centrifugal.

We’ve talked about the five types in another article, so they won’t be explained here (Read more on the subject matter in the Technical İnformation of # 114, which is available at

The aspect that will be addressed in this article concerns the way the compressor is installed together with the electric motor – which has no direct relation to the operating principle.

There are three classifications of compressors, according to this criterion:

  • Hermetic: when the electric motor is together with the compressor in the same sealed chamber (housing);
  • Semi-hermetic: when the motor is together with the compressor, in the same chamber, but this chamber can be opened, being fastened by screws and using seals;
  • Open: when the electric motor is not together with the compressor.
  • As this issue’s cover story deals precisely with semi-hermetic compressors along with Embraco’s entry into this segment (Read more on page 6), we address here mainly the differences between these types of compressors and hermetic ones (which are already well known by our readers, since they are Embraco’s main product).

The main aspects that differentiate hermetic compressors from semi-hermetic ones include:

Maintenance possibility

For having a sealed housing, hermetic compressors can’t be opened for maintenance. When the electric motor burns-out or any other problem occurs, the only solution is to replace the compressor.
While semi-hermetic compressors can be repaired in many cases, since access to valves, to pistons and other components is possible, as well as the motor. It should be highlighted the need to replace sealing elements in these models (the same occurs for open compressors).


One of the great advantages of the hermetic compressor is the extremely low incidence of refrigerant leakage.

This problem occurs more frequently in semi-hermetic ones and is even more common in open compressors.


In hermetic compressors, lubrication occurs by centrifugal force, which causes the oil to circulate. While semi-hermetic compressors have an oil pump, having what is called a forced lubrication. In these models, the oil, accumulated in the crankcase, is suctioned by the pump, which distributes it through the lubrication channels reaching the bearings, connecting rods and pistons pins.


Hermetic compressors are used in domestic refrigeration systems and compact commercial refrigeration and air conditioning systems. In turn, semi-hermetic compressors are mainly suitable for supermarkets and other commercial and industrial applications, as well as for large air conditioning development project systems such as shopping centers.


In general, one can say that hermetic compressors are less expensive than semi-hermetic ones – considering that the equipment in which they are used in is also simpler and less expensive. This is a factor that can, at first, call the attention of those who compare prices. However, it should be noted that these are very different products: it would be like comparing the cost of a car to that of a tractor.