View Full Version : Will this work?

12-04-2016, 10:28 PM
In order to keep oil at the compressor where the condensor is above the height of the evaporator, the liquid line just needs to immediately rise above the height of the condenser before it drops to the evaporator. This will help trap oil in the compressor.

Is that correct?

12-04-2016, 10:55 PM
Don't think so. Once it comes out the compressor you want it to come back!
Perhaps even the condenser coil could be thought of a type of loop like this as inlet goes in at the top then out the bottom (might have a distributor though).

A loop like that might be needed if evap or remote condenser was higher than compressor to stop liquid dribbling back during off cycles and getting into compressor cylinder depending on pipe layout
Think I've seen a one way valve on a water chiller once on the discharge line to the remote condenser. Told they were fitted after a compressor soon died after install.

Back to the question. Suction might need a slight bend up so oil there doesn't drain back down to evaporator perhaps.
Not a total loss as that loop be handy to hang you coat on.

Traps not my forte, have to stop and think a bit but how's that for starters?


Edit: Post I did yonks back and has drawing of pipe trap.

13-04-2016, 01:40 AM
I don't think so either,
put a P trap at outlet of evaporator to entrain oil accumulation in low pressure area ( evap ) back to compressor, there is a figure of traps every xyz metres for extra high lift suction lines.
Add extra oil to compressor as well for extra long and height separation.

monkey spanners
13-04-2016, 02:33 PM
Any oil that is in the liquid line will just get washed/dissolved along with the refrigerant, can't see the loop adding anything other than a restriction to the system.

If it was a discharge line and between the compressor and condenser that is a different case as its possible for liquid to run back up the discharge pipe into the head of the compressor and cause damage next time it starts.

Also there are times you want a trap in the suction line to stop any liquid running into the sump during off cycle though if the system is on pump down it is less of an issue.

13-04-2016, 02:49 PM
no :)


13-04-2016, 03:36 PM
I don't see any issues of losing oil in this configuration.
you have to add [if there isn't any] NRV on the discharge line to protect the compressor from liquid returning especially on cold days.
An oil separator can do you good.

pump down SV is enough. Don't let the low pressure to go too low, Adjust the superheat to maximum, this will help pulling oil back to the sump.

13-04-2016, 09:05 PM
Will liquid bank up a bit in condenser with this configeration??

13-04-2016, 09:39 PM
Maybe there was meant to be a subcooler circuit in the condenser as the liquid line seems insulated , can see no other reason to run it up there

Glenn Moore
14-04-2016, 12:52 AM
Hi Contactor
The answer to your question is NO.
Joe is on the right lines, by elevating the liquid line exiting the condenser it will increase the liquid sub-cooling by causing liquid to back up in the condenser coils. But I would be concerned about the possibility of vapour locking in the liquid line with this pipe work configuration.
On many Co2 systems the outlet pipe from the condenser is raised to just above the bottom row of the condenser tubes so that liquid floods the bottom tubes before exiting the condenser to give subcooling to the refrigerant.
This will have no effect on the oil circulating through the system.
Ps I trust the engineer who did the pipe work was F Gas registered , but somehow I doubt it judging by state of it.

Pps Andy (tayters) I read your old thread regarding the Dunham Bush oil control/hotgas dump system problem, if you want to understand how the system works give me a call Br Glenn