The need for hot gas (or suction) riser traps WHEN YOU ALREADY HAVE PROPER VELOCITY

[BronYrAur]

I am wondering why traps are needed at the bottom of hot gas or suction risers when you have enough velocity to return the oil? I see them in every reference I can find, but no one explains why.

I fully understand needing them for situations where the compressor unloads or otherwise stages. I can see why you would reduce the diameter of the riser or install double risers with proper traps. But that is not what I am asking.

My question is why do I need a trap when I have a constant speed single stage compressor and my pipe already has enough velocity? In my specific example, I have a 20 ton system with a remote condenser on the roof. I am less than 100 TEL, so I have sized a 1-3/8" OD hot gas line. I will have an inverted trap at the condenser (and understand why it is needed); but, the manufacturer also wants a trap at the bottom of the hot gas riser.

Why is this trap needed when my velocity will be over 2,000 FPM?

Thanks for you help

 

[DrRTU]

My guess, based upon ACC above compressor, minimize oil or liquid working backwards to compressor during off cycle. Most the details were developed for recip machines to avoid liquid in the cylinder . You may want to rethink is its a scroll.