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Semihermetic Compressors

Semihermetic compressors are larger refrigeration compressors where the motor and compressor are housed together but the casing can be unbolted, unlike hermetic compressors. They provide easier access for maintenance than hermetic compressors but are less efficient since the motor requires external cooling rather than using the refrigerant. Semihermetic compressors can achieve overall efficiencies over 70% and control capacity by making some cylinders ineffective or unload cylinders at startup to reduce starting torque.

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Baraa Al Sayed
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177 views1 page

Semihermetic Compressors

Semihermetic compressors are larger refrigeration compressors where the motor and compressor are housed together but the casing can be unbolted, unlike hermetic compressors. They provide easier access for maintenance than hermetic compressors but are less efficient since the motor requires external cooling rather than using the refrigerant. Semihermetic compressors can achieve overall efficiencies over 70% and control capacity by making some cylinders ineffective or unload cylinders at startup to reduce starting torque.

Uploaded by

Baraa Al Sayed
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Semihermetic Compressors

In larger sizes, refrigeration compressors are often semihermetic, that is, although motor and compressor

are within one casing, this casing may be unbolted, and the refrigerant does not flow over

the motor windings. Access for maintenance is straightforward, but the need for external motor

cooling which aids efficiency in cooling applications is no advantage in refrigeration operations,

and the cost is substantially higher than for hermetic units. As large motors are more efficient than

small ones, overall efficiencies of up to 70% or more are theoretically possible, and in multicylinder

compressors, capacity may be controlled by making one or more cylinders ineffective (e.g., by

holding the inlet valve open). Cylinder unloading at start-up is also a convenient way of reducing

starting torque.

These compressors (single or double acting) were developed to avoid the disadvantages of the

hermetic compressors. Semihermetic compressors are identical to the hermetic types,

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