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WhollyKow
03-05-2014, 12:14 AM
We have an ammonia-based plant run via Mycom W-series recip compressors. The installer provided MyCold AB68 oil, but there are some saying that is not the correct oil and could be the cause of some problems we've been experiencing. Can anyone please advise if that's an adequate lubricant or if we should be using something else? Thanks in advance.

RANGER1
03-05-2014, 01:01 AM
Whollykow,
Mycom recommend it for all NH3 applications as fully synthetic.
These oil prone to cause seal leakage if incorrect "0" rings used.
Is that your problem?
Also are they WB or WBHE compressors?

WhollyKow
03-05-2014, 01:30 AM
They are model N8WB's. We have had seal leakage once, but our big issue has been a complete seizing of one of the compressors due to some sort of sludge that bound the pistons to sleeves. Twice now we have completely rebuilt this compressor due to this mystery substance. The immediate thought was that it was due to moisture in the system but tests don't necessarily validate that concept.

We cut apart the oil separator (Henry COS-140) that serves this particular compressor and found this insulation-like material that was badly disintegrated. We believe this is the substance that made it's way into the compressor and caused the failure. We've replaced the oil separator.

We have been going at this issue for three years now without any definitive resolution. The compressor in question has just recently been shut down but ran for the last 9 months without issue. We will soon take the head off to see what it looks like. Hopefully the new oil separator and the two rebuilds have solved the issue. However, there are new refrigeration techs that are pointing at the Mycold AB68 as the cause. I am just a facility operator, not a refrigeration tech, so I am trying to learn how that may, or may not, be a valid possibility.

Magoo
03-05-2014, 02:11 AM
Hi Whollykow.
has there been any history of changing from mineral oil to fully synthetic oil with the system. May account for the sludge build up and damage to compressors.

WhollyKow
03-05-2014, 02:33 AM
I believe it's been the MyCold 68AB the whole time, however the installer recently said that they originally put PIR 68A in there. I can't find any MSDS or product description for that though. Does 68A indicate a mineral oil?

RANGER1
03-05-2014, 04:23 AM
I believe it's been the MyCold 68AB the whole time, however the installer recently said that they originally put PIR 68A in there. I can't find any MSDS or product description for that though. Does 68A indicate a mineral oil?

Maybe you should pursue the original supplier for more details on this mystery oil.
Once you can identify it then possibly ask Mycom or whoever supplies the MYcold oil about compatibility & your current situation.
I have seen one of our plants with a similar problem, it never had a oil brand or type change, so is a mystery also.

Grizzly
03-05-2014, 08:18 AM
Hi WK.
Your techs are correct to question the use of Oils.
Because with Mineral, AB and POE oils available, cross usage can have disastrous effects.
With Indeed a sludge being one of the side effects of cross contamination due to newer oils being added to older!
However your AB oil is totally compatible with Ammonia and had a mineral ever been present then that is acceptable as well.
See Attached.
I am assuming your comps have water cooled heads?
Out of interest if so! Where is the head cooling water taken from?
I have seen all sorts of issues due to the commonly used condenser tower sump being the supply.
This type of system makes huge sense but occasionally the water treatment guys used their chemicals in large doses, especially if you the customer are paying for them!
With the phosphate based chemicals that are sometimes used.
You can attack the carbon in the castings eating the fabric of the cast steel, making it soft to the point that it can be dug out with a spoon.
When descaling the heads are the greying deposits there?

This is pure speculation at present but may lead you to another possible cause and effect?
Basically your oil is correct, insulation is an inert material (To my Knowledge anyway!)
Therefore I don't think this is the cause, look for other changes coinciding with your failure timescales.

None of us are infallible and your techs are taking the logical route, yours is indeed a strange issue so please keep us informed, we can all learn.
Grizzly

Grizzly
03-05-2014, 11:31 AM
Back again.

It's also worth noting your oil sludge is more likely to be a direct cause of overheating due to many factors.
One of which can be poor head cooling, due to poor flow through heads.
The TDS of chemically treated cooling water has a tendency to come out of suspension when subjected to the heat within the heads.
Ergo! poor head cooling, poor water flow and heavily carbonised Oil.
Just a thought!
Grizzly

RANGER1
03-05-2014, 10:01 PM
Just to ad to Grizzly's advice, try running compressors with out oil return from compressors as well.
Drain excess oil from them when required & discard oil.
Get an oil analysis done called "full suite" which covers everything, hopefully it could shine some light on something.
As Grizzly's says clean heads & also oil cooler & possibly internal jacket around discharge of compressor.
Heads should be relatively cool to touch where water jacket is on each head.

It would be good to have some pressures & temp of your compressors.

suction pressure & temp on suction line into compressor

discharge pressure & temp (max 140 deg C).

oil temp (max 50 deg c).

oil pressure.

cooling water in & out temps of each compressor.

speed of compressors, direct drive is easy, belt drive need motor speed,both flywheel & pulley diameters.
Maximum speed should be 1200rpm.

G_Short
30-07-2014, 09:03 PM
Mycold AB 68 is their lubricant for Ammonia and R22. Has been for many years. They prefer this over other types of lubricants due to their own long time experience.

PRESS
31-07-2014, 02:35 AM
Together with all the other valuable advise from others I strongly recomend oil tribology tests. Here in south africa the most common oil tribology place we go to is wear-check. this should be able to point you in the definate direction with decision making. You will be able to know what is desolved in your oil. This can help you zero in on the cause of the problem.

I normally implement a regular oil tribology test for the various plants we do maintenance on as part of the critical data we collect, compile and analyse for preventive maintenance. This at least shows us what is building up in a particular system.