semihermetic

Semihermetic refers to a class of compressors used primarily in refrigeration and air conditioning systems. In a semihermetic design, the motor and the compression mechanism are housed inside a single metal shell that is sealed to contain refrigerant and oil. Unlike a fully hermetic unit, the shell is bolted shut rather than welded, enabling access for inspection, servicing, or component replacement without destroying the housing.

Construction and operation typically involve a crankcase inside the sealed shell that holds lubricating oil and connects to the compression mechanism, which may be piston-type or screw-type. The motor drives the compressor through a shaft or crankshaft, and seals and gaskets maintain containment of refrigerant and oil. Service ports and removable components allow maintenance or part replacement, making semihermetic units more serviceable than fully hermetic ones.

Compared with other designs, semihermetic compressors offer a compromise between serviceability and compactness. They generally provide easier field servicing and potential refurbishment, while remaining more compact and cost-effective than open-drive systems. However, they may incur slightly higher leakage paths and cooling challenges due to the bolted housing, and the overall efficiency can be somewhat lower than that of a welded hermetic unit.

Applications for semihermetic compressors include commercial and industrial refrigeration, air conditioning systems, and heat-pump installations where service access and mid-range capacity are desirable. See also hermetic compressors and open-drive compressors for related designs.