Foamy oil in Bitzer Octagon

[Fridgy Dave]

I've got an old R22 freezer room running on three compressors and one has been changed to a Bitzer octagon not to long ago and the oil is constantly foamy and tripping out on the optical sensor. The compressor superheat is good and I have replaced the oil in the comp with fresh B5 oil but it continues to do it. I was wondering if this is common with octagons considering they have no oil pump?

[chemi-cool]

Foam caused by liquid refrigerant returning to the compressor.
Check the super heat again, it might be too high.

[750 Valve]

R22 on low temp = troubles

What are the suction and discharge pressures, what is the suction superheat and the comp discharge temp?

Normally R22 on LT is done with 2 stage comps with desuperheating between stages. Have you measured the oil temp at all?

[Fridgy Dave]

16psi Suction190psi discharge18k compressor superheat90deg discharge tempNot sure where I could get an oil temperature reading from

[The Viking]

Dave,
When you say the superheat is 18K, how do you measure it?
At 16 psi the saturated temperature of R22 is about 24ºC, 18K superheat would give a gas temperature of -6ºC and there is no way that would be able to sustain a freezer.

Assuming it is a single stage system, are you sure it is operating on R22?
What are the actual temperatures? Room? Liquid? Suction line after the evaporator by the TEV bulb? Suction line before the compressor (at least 6" before)?



.

[Fridgy Dave]

The superheat I was referring to was the compressor superheat not at the TXV. It is higher due to poor insulation on the suction and accumulator not insulated which is currently getting repaired.

[750 Valve]

90 degree discharge temp is not overly massive for R22, I wouldn't waste time looking at oil temp anyway. I have seen R22 up over 100 degrees on LT and the oil starts to have issues.

By the sounds of the system you have described it might be an old Franko's or a Food For Less insitu freezer - is it a hot gas defrost single system with suction accumulator? If so have you watched it defrost and what is the defrost parameters and are there any PM valves fitted to the coils?

[D.D.KORANNE]

1) expansion valve might have debris which would not permit valve to move in closing direction during low load..........since foaming is indicative of liquid escaping from oil.
2) check crank-case heater ..... May be out of order.

[RANGER1]

90 degree discharge temp is not overly massive for R22, I wouldn't waste time looking at oil temp anyway. I have seen R22 up over 100 degrees on LT and the oil starts to have issues.

By the sounds of the system you have described it might be an old Franko's or a Food For Less insitu freezer - is it a hot gas defrost single system with suction accumulator? If so have you watched it defrost and what is the defrost parameters and are there any PM valves fitted to the coils?

I would check sump temp to make sure its not to cold.
Should be warm at least 30-40 deg C

[Magoo]

Hi Dave.
I am not familar with compressor, but if it does not have an oil pump as such then there will be splashers / beaters on bottom of big end caps, to flick oil everywhere, hence the foamy sight glass, optical level sensor probably not suited

[750 Valve]

Hi Dave.
I am not familar with compressor, but if it does not have an oil pump as such then there will be splashers / beaters on bottom of big end caps, to flick oil everywhere, hence the foamy sight glass, optical level sensor probably not suited

Bitzer manufacture the OLC-K1 for oil level protection of their splash fed compressors (actually not splash fed they use a centrigugal setup to lift oil and pump it through crank) it screws directly into the housing of the compressor at the front bearing

[Sandro Baptista]

Also check the oil level. It could be very high so creating a big shake...

[Magoo]

Hi 750
like I said I did not know the compressor, but as you explained, an excuse for an oil pump. Sounds very similar to the carrier oil feed system on O6E and O6D a slinger thingo on crank , high volume low pressure.

[nealo]

would switching to POE oil make a difference?
and dose the compressor have any liquid cooling that may not be operating correctly?

[Fridgy Dave]

The comp has an OLC-K1 protection device on it and has tripped previously due to the oil being foamy, it does have hot gas defrost with PM Valves. I ran each evap through a defrost and still never had liquid back to the comp but the oil continues to foam. Sump temps are always above 50 degrees

[Sandro Baptista]

Is it not too high the oil level?

[750 Valve]

The comp has an OLC-K1 protection device on it and has tripped previously due to the oil being foamy, it does have hot gas defrost with PM Valves. I ran each evap through a defrost and still never had liquid back to the comp but the oil continues to foam. Sump temps are always above 50 degrees

During defrost what is the suction pressure and discharge pressure? Have you actually put a probe on the suction line during defrost? The SST will likely be quite high and may not show up as a cold (to the touch) suction line or compressor.

What is the PM valve set at during defrost? How long is the defrost cycle?

Oil doesn't just foam, its likely got to do with the HG defrost cycle in the system you have described.

You could always ditch the OLC and wire the traxoil through the control circuit to shut off on low oil level. It won't protect the comp if the oil is foaming though and the bearings aren't getting what they need.

[Fridgy Dave]

Off hand I can't remember the pressures but I did have a thermocouple clamped to the suction pipe at the comp and it did maintain a good level of superheat. I have heard that running the comp with a high discharge temp over 80 degrees for long periods will turn the oil acidic, I don't think this to be the case but rather the oil has been corrupted by other means and i am going to change the oil in the comp and separator.

[750 Valve]

Is it possible that whoever changed the comp left the BSE32 in it when they installed it? Meaning you have a mix of B5 and BSE32 in there?

You can download all the specs on the oil from Bitzer website which will state the max recommended oil operating temp - from memory its 55 degrees oil temp. Being an insitu room and running a -25SST is helping keep the discharge temps down, if it was running at -30SST the discharge temp would be getting up there.

Hope a fresh charge all round fixes it for you.