Oil Entrapment on the Low Side Basics

[one_servant]

Oil Entrapment on the Low Side Basics

Okay engineers I need some sound advice about the basics of oil entrapment in the low pressure side of single stage systems like we build. I’m getting down and dirty with my component arrangement and I need some good advice about routing my piping on the low side.

The reason for my query is that it looks like I may have to make some upward swings to fit the pipe-work inside my case in a civil manner. What do I need to understand in order to prevent serious oil problems in my system? What I’m really looking for here are the basic “rules of thumb”. I need a sound understanding of this theory before I go on… :fact:

Thanks in advance! :D

[n00b 0f l337]

I doubt in our systems you could cause oil problems without a 2 or 3" ID pipe standing vertically and trying to enter at the bottom and leave at the top.

[EvoCarlos]

rule of thumb
the oils in the gas :up:
as nol said system is to small to worry about
and the oil is in the gas so most parts are lube'd up when running

[Duzter]

You would need a rise of 1,5-2 meters before you need to make oil pockets (english word?).

[DetroitAC]

Been thinking for a while on this one...
Oil entrapment being a problem sort of depends on your definition of "problem".

If the definition of problem is the compressor runs dry of oil and seizes:
A single stage is just far too small to ever run out of oil in the compressor, the system likely just cannot store that much oil. Of course if you build something really unusual, then you might be able to trap all of it.

If the definiton of problem is just that you have oil pooling where you don't want it to, then I think that actually happens all the time in some of the builds I see. An example is a big muffler or strainer shell laid horizontal to act as an accumulator. I think they act as accumulators somewhat, and gradually fill up with oil when a system is idle. At full load, they probably empty out rapidly. Of course they also could always have an oil puddle in them, and the puddle might just be smaller at full load than at idle.

Oil puddling will really only cause you problems if you are trying to store some liquid refrigerant on the low side, and are unable to because you have an oil trap, or maybe if you are puddling oil where you would like to be exchanging heat.

As far as rules of thumb go, there are standard line sizes for suction lines that are horizontal and lines that are vertical. I haven't worked the tables backwards, but I think most likely they are velocity based. I can tell you from my experience looking at suction line sight glasses that indeed the oil is shoved along the bottom of a suction line in a sort of wavy stream, and that it is very velocity dependant. Standard line sizes are listed in the ASHRAE handbooks, but probably also a lot of other sources. As a general rule, for hermetics I think using the tube size that mates with the suction connector is a safe way to size suction piping.

[Duzter]

Could you explain me the term "oil puddling", not that good at more technical english. :)

[DetroitAC]

oil pockets

[one_servant]

Man, thanks guys, especially Detroit. That's a pretty complete answer. Essentially that's what I wanted to find out with regard to putting the compressor in danger or in causing some sort of critical failure in any number of the locations that heat exchange is taking place. I feel a lot better with being ever so creative in my copper bending now… :yepp:

…famous last words? :shrug: I hope not. :up: