Parallel compressors

[A.Mortezania]

Dear Friends,
I have a question.

Regarding compressors in parallel systems, Some sources such a ASHRAE emphasize on this matter that beside of suction and discharge pipes we must join oil line + gas equalizer line such as photo at below :


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Some companies such as LG and …. use this rule when they want to parallel compressors.

But some other sources such as EMERSON (COPELAND) on SCROLL compressors and CARLYLE (CARRIER) on semi-hermetic compressors just join suction/discharge/oil of crankcase (no need gas equalizer line). See example below :

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Which one say true ??

Sincerely yours.

[Brian_UK]

.....Both, capacity controls, oil level controls all can have a bearing on the piping required.