View Full Version : Frick RXF Oil Level Fault caused by liquid injection.

Mike W
19-11-2012, 07:49 AM
Has anyone experience any issues with a Frick RXF 39 compressor set where liquid injection causes the oil in the oil separator to foam so much that it cause the oil level switch in the oil separator to trip.
We have set up the liquid injection as per the book but when the liquid injection activates and the discharge temperature comes under control we get excessive foaming in the oil seperator that eventually.
The compressor set used to run R22 and now has been converted to ammonia.
All the liquid injection valves have been replaced with OEM replacements and all seems correct.
We have even replaced the oil injection orifice to the correct size.

Operating conditions.
-12C suction R717
32C cond.
Discharge temperature 60 degs( slightly high to keep plant running)

Any ideas?

19-11-2012, 09:34 AM
Does the compressor have an external oil cooler?

60C discharge still has a bit of grace, up to 75 or 80C at full load is ok.

If it has an external cooler it shouldn't need injection majority of the time, turn off the injection & watch the discharge temperature.

Set injection cut in temperature for 75C or so & see if that settles the oil level down.

19-11-2012, 11:15 PM
The oil was changed out or?

This is an all mechanical liquid injection components that is Strainer-Solenoid-TXV and a outlet Pressure Regulator as a biasing valve....Right? The wrong TXV or too big a TXV for the compressor would be first guess. But presuming that corresponds:

If there's a lot of water in the refrigerant, or in the oil, you will get some pretty strange things going on as well.

Other than that: there are (3) conditions that lead to overinjection: Equalizing pressure too low; load too low (compressor not loaded up); and liquid carryover. If you are carrying liquid over, you should be able to close the liquid flow to the injection valve train and the separator will continue to froth for some time; then the oil temperature will slowly start to rise. If the frothing quits immediately you can presume you have limited carryover....

Raise the equalizing pressure (open up the little OPR) and watch for the froth to quit....Note that if your head pressure is very low you will never get the equalizing pressure to rise. If it doesn't rise when you dial the OPR up, needle down on the instrument valve where it connects to the suction strainer housing.....If you close it right off the flow through the TXV should stop altogether and pretty promptly; and your oil temp will go up almost immediately. If your EQ pressure is reading right: I would start breaking down that side of the hydraulic tubing and clear it out. There's probably something blocking the tube between the TXV Body and the downstream side of the OPR.

If there's a lot of water in the refrigerant, or in the oil, you will get some pretty strange things going on as well.

If you close the HP liquid upstream of the TXV and the machine continues to run cool, you definitely have liquid carro

Mike W
20-11-2012, 08:08 AM
Thanks for the feedback.
No there is no external oil cooler, it rellies on liquid injection only. The plant was converted to ammonia as part of a major rebuild of the plant. The liquid injection worked fine on R22. The plant was evacuated to 100microns for a week and throughly cleaned before hand. New oil was installed in all the compressors. The liquid injection expansion valve was sized and supplied by Frick/JCI.

I have tried all the above xuggestions and messed around with different setting and still get the same result with one exception.

There are two RXF 39 compressors, one has no been touched since it was converted to ammonia, but the second one was replaced as part of the maintenance program.
As part of installing the new compressor a oil injection orifice was fitted according to the information provided with the new compressor. This was a 0.193" orfice and is installed in a port just below the econimiser connection to feed oil into the rotors to provide cooling. On the R22 compressor it has a smaller orifice of 0.136" fitted and this is correct according to the data supplied. The interesting thing is the the compressor with the smaller orifice was running alot better and was easier to setup than the one with the larger orifice.

I have worked on alot of Mycom compressors and when the use a water cooled oil cooler(external) they inject oil into the rotor housing seperate to the lubrication feed, when they use liquid injection they inject liquid refrigeratant into the rotor housing, again seperate to the lubriaction feed. The question I have is why does the Frick inject the same amount of oil into the rotor housing regardless of the oil been water cooled by an external oil cooler or by liquid injection. I am thinking that there is excess oil mixing with the liquid refrigerant in the rotor housing that causes the oil to retain some of the liquid until it enters the oil seperator where the liquid boils out of the oil and creates foam.

Any thoughts?

Cheers Mike

20-11-2012, 08:09 AM
Maybe you need to verify that dsicharge temp reading is correct.
I would have thought the liquid injection valve should control discharge & oil temp to approx 50-55 deg C anyway, depending on oil type.
Discharge & oil temp should be near enough the same.
I am onlty familiar with Danfoss TEAT injection valve which you adjust valve opening temperature & it modulatesat that ie 55 deg C.
What type or brand of valve is it & explain more detail in the setup of if you can.
There may even be a few options on injection port.

20-11-2012, 10:11 AM
Interesting information about the*oil injection orifice. Is the*0.136" (smaller) item available from the original compressor? Probably worth trying.

I'd agree that excess liquid refrigerant is getting into the seperator - liquid injection is such a compromise compared to external cooling.

20-11-2012, 10:17 AM
I guess you already have this!

Mike W
21-11-2012, 08:16 PM
Thanks for the feedback,
Yes I have several copies of the service manuals for the Fricks with all the information on the liquid injection. We are waiting for feedback from Frick as the only documentation about the oil injection orifice I have came with the new compressor.

And yes I agree liquid injection is a cheap and nasty way of compressor cooling and would not install.

22-11-2012, 01:08 AM
Hi Mike W.
are you using the low VI port, prg says 2.4 kg/min flow for injection, 54' C oil and discharge temp..

22-11-2012, 10:04 AM
Hi Mike W.
are you using the low VI port, prg says 2.4 kg/min flow for injection, 54' C oil and discharge temp..

Magoo I get the following, so you may recheck you had on liq inj cooling.

-12 sst +32 sct
71 deg C for oil/discharge temp using low Vi port.
set 3.5 Vi
oil flow in oil inj 33.4 l/m
3/4" Danfoss ICM 20A for liquid injection ( I like this better than the original system of adjusting stuff, how it works I don't know).

Maybe you used water cooled oil cooler setting for 54 C oil temp

22-11-2012, 10:36 PM
Hi Ranger1
Interesting . What figure for suction superheat did you apply. I am running select version 4.1, oldish

23-11-2012, 04:43 AM
Hi Ranger1
Interesting . What figure for suction superheat did you apply. I am running select version 4.1, oldish

Maybe its not right, as your temp sound normal to me.
I put in other refrigerants & discharge changes, interestingly R22 is same 71 C discharge temp?

05-12-2012, 12:19 PM
Had the same problem several years ago on an RXB 50. After trying many different things, Frick suggested we incorporate a time delay relay into the oil float circuit.

07-12-2012, 08:13 PM
I had this problem and solved it with increasing liquid injection setpoint

08-12-2012, 07:59 AM
The smaller oil orifice is required with R-22 as this refrigerant will already be saturated with some oil. Ammonia holds less oil therefore the need for a larger orifice on the oil feed to the rotors. With the smaller orifice installed on the ammonia unit you get less of an oil seal between the rotors and the result is some gas bypassing. This results in higher discharge temperatures which is why you dont have any foaming on this unit. However this is not the correct solution as your unit will be less efficient. I would suggest that the discharge temperature be raised by 5K by closing the liquid injection valve. If there is a solenoid on the liquid injection line try setting the setpoint so that it opens sooner. If the solenoid opens when the liquid injection valve is fully open, a large volume of liquid may be injected before the bulb on the discharge line senses the drop and closes the injection valve. By opening the solenoid sooner the regulation may start with a lower valve opening and better temperature control.