PDA

View Full Version : Foaming Oil



Futsal1st
27-02-2008, 08:31 AM
I have a semihermetic compressor on R22 with TX valves. It is a DX plant with short piping runs. I have noticed the sight glass is showing the oil foaming (the sight glass is full of foam). There is no obvious signs of liquid flood back (ice on suction or rattling). The operation appears ok (450kpa suction and 1500 kpa discharge on air cooled). But I am concerned with regard the foaming. What else could be the possible options of foaming oil. :confused:

Cheers

Chunk
27-02-2008, 09:20 AM
Hi Futsal1st.
Do you have a crankcase heater fitted to the compressor?
Does the foam only appear upon startup then dissappear or does it foam all the time?
Chunk.

The Viking
27-02-2008, 10:26 AM
What's the superheat?

Springbok
27-02-2008, 11:47 AM
Hey Futsal1st.Welcome to the site.If there is a crankcase heater fitted,is it permanently on?Is there a oil filter on the oil return line?When last was the oil changed?

dsp
27-02-2008, 11:56 AM
Hey futsal1st,
What brand of compressor?
dsp

Futsal1st
28-02-2008, 12:02 AM
Thanks guys,
This plant has been installed for some 10 years and seems to have run ok in the past. Its a Bitzer semi hermetic 6 cyl. It doesn't have a crankcase heater. The ambient temp in the plant room was 26C when I inspected it and the foaming wasn't just on start up, it was continuous.
I didn't check the S/Heat (2 TX valves for this circuit). I checked the suction isolation valve at the compressor and it didn't feel overly cold (suction was 450kpa, around 4C). By the sounds of that question, you suspect minor flood back from poor superheat settings. Is that right?

The Viking
28-02-2008, 12:08 AM
Well, it is a thought....
If the oil is foaming, then there must be liquid refrigerant boiling off and that must be coming from somewhere....

nike123
28-02-2008, 12:15 AM
Well, it is a thought....
If the oil is foaming, then there must be liquid refrigerant boiling off and that must be coming from somewhere....
And if it is constant, then it must be problem with low, or absolute lack of superheating at compressor intake.

Gary
28-02-2008, 12:17 AM
Since it is continuous, I would suspect that the oil is churning as opposed to foaming. It can be difficult to tell on some compressors. If it were continuously foaming (boiling off refrigerant) the crankcase would be very cold.

nike123
28-02-2008, 12:41 AM
Since it is continuous, I would suspect that the oil is churning as opposed to foaming. It can be difficult to tell on some compressors. If it were continuously foaming (boiling off refrigerant) the crankcase would be very cold.

Today is my first heard of term "churning"! Did you mean this by that term:
http://tinyurl.com/2ec89q

Futsal1st
28-02-2008, 01:03 AM
Thanks very much for the great help guys. To me the direction appears S/Heat as the first stop. There a 4 systems in this plant, all identical and not connected. Only 1 has the problem. Much appreciated. Cheers (Woo Hoo , 3 posts, I'm racing ahead)

Gary
28-02-2008, 01:08 AM
Hmmm... I'm not sure if my definition agrees with theirs or not. I am referring to lots of action in the crankcase oil without involving the boiling off of refrigerant. The oil in some compressors looks like it is foaming when it is not.

What I am sure of is that when liquid refrigerant continuously boils off in the oil, it cools the oil and the oil cools the bottom of the compressor. Foaming results in a cold crankcase.

nike123
28-02-2008, 01:21 AM
Hmmm... I'm not sure if my definition agrees with theirs or not. I am referring to lots of action in the crankcase oil without involving the boiling off of refrigerant. The oil in some compressors looks like it is foaming when it is not.

What I am sure of is that when liquid refrigerant continuously boils off in the oil, it cools the oil and the oil cools the bottom of the compressor. Foaming results in a cold crankcase.

That is what is described in application bulletins of Copeland hermetics. Somewhere I have this, and If I found it I will post it here.

The Viking
28-02-2008, 01:31 AM
Thanks very much for the great help guys. To me the direction appears S/Heat as the first stop. There a 4 systems in this plant, all identical and not connected. Only 1 has the problem. Much appreciated. Cheers (Woo Hoo , 3 posts, I'm racing ahead)

Is it too late for me to back track now?

I actually thinks Gary might be on to something.

Some semis will create a lot of movement in the oil sight-glass (churning) if they are rotating the "opposite" way.
So before you get too concerned about the foaming, assuming the crank hasn't condensate forming on the outside, check the phase rotation compared to the other compressors on site.

Just a thought.

nike123
28-02-2008, 01:43 AM
Is it too late for me to back track now?

I actually thinks Gary might be on to something.

Some semis will create a lot of movement in the oil sight-glass (churning) if they are rotating the "opposite" way.
So before you get too concerned about the foaming, assuming the crank hasn't condensate forming on the outside, check the phase rotation compared to the other compressors on site.

Just a thought.

Do you mean, that if one semi-hermetic is turning in one direction and other semi-hermetic is turning in opposite direction, that one of them is going to make more "churning" then other one?

The Viking
28-02-2008, 01:57 AM
Do you mean, that if one semi-hermetic is turning in one direction and other semi-hermetic is turning in opposite direction, that one of them is going to make more "churning" then other one?

Yes,
One would splatter oil on the wall opposite the sight glass, the other one straight on to the sight glass.


This is well illustrated on "old" copeland/dvm/carrier compressors that used to have 2 oil sight glasses on their tail end, one on each side of the shaft.
When the compressor were standing you had (not surprisingly) an equal level in both glasses but as soon as the compressor started (if you were able to see the levels) one went to the bottom and the other one went to the top with the oil swirled around quickly (churning)

nike123
28-02-2008, 02:05 AM
Interesting, newer taught about that.

taz24
28-02-2008, 02:41 AM
I have a semihermetic compressor on R22 with TX valves. It is a DX plant with short piping runs. I have noticed the sight glass is showing the oil foaming (the sight glass is full of foam). There is no obvious signs of liquid flood back (ice on suction or rattling). The operation appears ok (450kpa suction and 1500 kpa discharge on air cooled). But I am concerned with regard the foaming. What else could be the possible options of foaming oil. :confused:

Cheers


Another thing to look for.
Some compressors and I think Bitzer is one of them deliberatley direct the return oil onto the oil sight glass so when the machine is running you can see that the oil is returning and being circulated through out the comp.

Just a thought.

taz.

balam
28-02-2008, 06:44 AM
Some thoughts:
° The foaming could be due to the pressure
difference between the high and low side
the liquid contained in the oil get flashed.
° If foaming happens all the time could be
the realief valve in the oil pump is opening
and bypassing the oil to the crackase.
° If the compressor has a capacity control
valve, it coud not be working properly.

Cheers

750 Valve
28-02-2008, 07:43 AM
I have seen this directional churning gary is speaking of as well, not so much on single stage bitzers, more on the compound 2 stage machines they make - massive oil churning on the sightglass. Like suggested by balam it may be an incidence of oil bypassing into the sump and creating the turbulence. Try checking the oil pressure and compare it to the others on site.

Chunk
28-02-2008, 10:43 PM
Hi All.

I had the same theory about churning and i checked all my standalone compressors earlier(bitzers) and yes they all churn.this looks like there is a lot of foam in the crankcase.

I also noticed that on one of my packs which has 4 bitzers on it that i had the oil seperator passing discharge pressure
back into the oil regulators and this was causing the oil to foam up. sorted with my hammer.

Chunk.

Gary
28-02-2008, 11:25 PM
I also noticed that on one of my packs which has 4 bitzers on it that i had the oil seperator passing discharge pressure back into the oil regulators and this was causing the oil to foam up. sorted with my hammer.

I hope that works out for you. With my luck I would end up back out there in a week or so, changing oil and filters and rebuilding the separator. You might want to change the oil filter and cross your fingers.

Chunk
29-02-2008, 12:36 AM
All in Hand.

Due to new health and safety b@ll@x someone has deemed it necessary that when working with pressures higher than 1 psi that we need another person present in case a nuclear explosion happens.

I can remember when 1st fixes used to matter.

I also found out today i cant use my wetvac to clear blocked drains because the noise might deafen someone as they walk passed.

The world is coming to an end.

Chunk.

lowcool
29-02-2008, 06:53 AM
oil seperator sounds most feasible

powell
29-02-2008, 07:01 AM
That is what is described in application bulletins of Copeland hermetics. Somewhere I have this, and If I found it I will post it here.
nke123

Here are two links to the the Copeland AE bulletins that are probably what you are referring to.

http://www.hvacrinfo.com/cope_ae_bulletins/TAE1281.PDF
http://www.hvacrinfo.com/cope_ae_bulletins/TAE1182.PDF

=========================================
Futsal1st

You could also have a pressurized crankcase as well. Cylinder walls worn due to high heat, high pressure gas re-entering the crank. We can discuss this further if needed.

nike123
29-02-2008, 11:30 AM
nke123

Here are two links to the the Copeland AE bulletins that are probably what you are referring to.

http://www.hvacrinfo.com/cope_ae_bulletins/TAE1281.PDF
http://www.hvacrinfo.com/cope_ae_bulletins/TAE1182.PDF

=========================================
Futsal1st

You could also have a pressurized crankcase as well. Cylinder walls worn due to high heat, high pressure gas re-entering the crank. We can discuss this further if needed.

Yes, that is it. Thanks Powell.

techie
29-02-2008, 04:48 PM
believe me dude thats liguid wash back too much liquide coming back into the compressor before or try flushing the whole system

nike123
29-02-2008, 04:58 PM
believe me dude thats liguid wash back too much liquide coming back into the compressor before or try flushing the whole system

When you presenting these statements, it would be nice, that you explain us how you came to that conclusions, and explain how to flush the hole system, so others could benefit from your knowledge.

techie
29-02-2008, 05:02 PM
what is that on psi

nike123
29-02-2008, 05:08 PM
what is that on psi

http://www.onlineconversion.com/pressure.htm