I've seen the piping you describe and I've (more often) not seen it. I think it is a stylistic thing at some fabricators. Probably a pipe fitter put something like your Lira Loop on a package that (probably for other reasons) worked out especially well. That shop then made the loop part of their standard and others copied it. I can't come up with a fluid-mechanics reason for the loop, and I've operated many flooded screws without it that worked out fine.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

Thanks for the reply, I think that this pipe configuration is due to avoid noise problem or vibration but I'm not able to found in licterature something relatives to my idea, but maybe it was a techincal choice of someone and after that a lot of people copy and paste...but I've some dubts.

My understanding is that the loop is commonly included for thermal expansion. The discharge piping from compressor to oil sep can have quite a temperature rise from ambient to operating temps, the loop keeps that expansion from putting force right on the compressor discharge flange.