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air compressor bane: water condensing in crankcase oil

808Dave

Plastic
Joined
Aug 14, 2015
A bit over a year ago I completed a prolonged, expensive and at times excruciating rebuild of a Quincy reciprocating compressor (model 340-33) that had fallen victim to unseen water-accumulation in the crankcase oil. In this model (with no sight glass) condensed water builds up below the oil and might or might not show up on the dipstick until it's too late. It's not a nice, clean interface of water-to-oil, but rather a nasty globular rust-water-oil mix that's thick enough to dam up random areas on the bottom, so it won't even drain out by gravity. I just spent an hour or so with both side-covers off, swabbing out all the glop that I could reach.
Condensation is clearly a huge problem for me, but I'm not sure why. I'm in Honolulu, so it's usually fairly humid. But there's not much of a daily low-temp swing that (in my mind, anyway) would account for the internal condensation. I suppose it's possible the condensation is primarily in the top end, where it gets much hotter during compression, and trickles down through cylinders between cycles and overnight. Whatever is responsible, I ended up with well over a cup (maybe two or three - it's impossible to tell without decanting and even maybe centrifuging the glop to see what's water and what's oil).
This compressor is essentially hobby-use, so it's never going to get run as these are 'recommended' to run. But even if it were run daily, I don't see an exit path for condensation. The crankcase is sealed, other than an active extraction path (via an external 1/4" tube that ties into an intake above, in the head) - and it would be equally bad to have condensation trapped up there.
After about three hour-meter hours of run time, I found that the oil level was a bit HIGH (because of the glop accumulated below it) and this time, there was a telltale streak of brown glop on the dipstick.
Here I go again.
I'm thinking I will set up a small pump that would circulate the oil - and any accumulated water - through an external reservoir (ideally it would be a huge glass bowl with bottom-drain, so I could see at a glance whether there was drainable water, more glop, etc) and then back into the crankcase. If I could, I'd find a way to spray the returning oil up into the cylinders, to help wash down anything that might be accumulating up there. I already modified the sump with a bottom-drain port (vs the stock side-port) to maximize the drainage. I'm hoping that if this recirc system can be started up with new oil, the glop won't have a chance to accumulate on the bottom of the crank-case, and instead will be washed out into my new external separator system. I plan to time it such that it keeps circulating for X minutes after each compression cycle.
But you know, if there is an easier way, I'm all ears.
BTW, though I'm leery of taking lubricant shortcuts, the Quincy oil ("Quin-CIP," ISO100, SAE30) is painfully expensive and not even available here in larger-than-quart size, so I'd appreciate any lubricant-afficionado recommendations for good-but-cheap alternatives, at least for what I expect will be a flushing-out period before I replace it with the factory stuff. Synthetic oil is apparently a bad idea in this setting because it is somehow much more susceptible to water infiltration - so I think I can rule out any synthetic substitutions.

Ideas?

Thanks all - Dave
 

dalmatiangirl61

Diamond
Joined
Jan 31, 2011
Location
BFE Nevada/San Marcos Tx
When in Texas, and used intermittently, my Quincy would get milky oil, There were 2 solutions, change oil, or run it hard with the bead blast cabinet. You need to run it hard for an hour or so to get it hot enough to cook out the moisture.
 

Garwood

Diamond
Joined
Oct 10, 2009
Location
Oregon
Quincy 340 is not a hobby compressor. It takes an hour or so of continuous running to get one that size all the way up to temp.

Use any cheap 100 weight hydraulic fluid in the sump. My Quincy's are all currently running Mobil DTE heavy in their sumps because I have a few 5 gallon buckets of it. I have run 68 weight hydraulic fluid in them, but you can hear the rods rattle in the hot summer months. I would only recommend 68 for cold winter use.
 

Bobw

Diamond
Joined
Feb 8, 2005
Location
Hatch, NM Chile capital of the WORLD
You actual answered your own oil question.. And Garwood gave you half of it, and I'll tell you the other half.. SAE30, just straight non-detergent 30 weight.. About as cheap as you can get for a non-standard/non-car... oil... dinosaur oil, not cooking oil.

The way you get moisture out, you also know that, you run it until it gets HOT.. And that drives the moisture out. But you don't want to do that, and I do not blame you, that sounds like a big electric bill to me.

One thing I would do is vent the crankcase. If its sealed, then even if you drive off the moisture, Where does it go?
I'd start with venting the case first.. And in a month, if that doesn't work, I'd look at heating the oil up once a month
to drive off the moisture.. Maybe one of those dipstick heaters for diesels..

Seems to me that pumping oil out and having a separate reservoir would be nothing more than a pain in the ass.
 

808Dave

Plastic
Joined
Aug 14, 2015
You actual answered your own oil question.. And Garwood gave you half of it, and I'll tell you the other half.. SAE30, just straight non-detergent 30 weight.. About as cheap as you can get for a non-standard/non-car... oil... dinosaur oil, not cooking oil.

The way you get moisture out, you also know that, you run it until it gets HOT.. And that drives the moisture out. But you don't want to do that, and I do not blame you, that sounds like a big electric bill to me.

One thing I would do is vent the crankcase. If its sealed, then even if you drive off the moisture, Where does it go?
I'd start with venting the case first.. And in a month, if that doesn't work, I'd look at heating the oil up once a month
to drive off the moisture.. Maybe one of those dipstick heaters for diesels..

Seems to me that pumping oil out and having a separate reservoir would be nothing more than a pain in the ass.
Funny, I was on my way back from NAPA with all the quarts of SAE30/ISO100 non-detergent they had on their shelves around the time your message must've come through (not sure why this forum - like some others - persistently will not notify me...) But I'm not down for the 'change it often' scenario: too much waste, too much chance of running water through the lube system without knowing it's time to change, and too much chance of what's shown in the photo below recurring. I might be able to centrifuge the stuff to clean it up, but that's a bunch of setup time.

Problem with JUST heating the crankcase, whether by accessory heater or by running it for prolonged periods, is, as you say, where the vapor can be expected to go, other than "up" into the cylinders (arguably worse than keeping it in the oil). There clearly isn't enough ventilation in the stock setup. Been thinking about boring two holes in one or both side-covers, sufficient to move low-velocity heated air through the crankcase, set up to keep the hot air moving for some adjustable period after each compression cycle - but this could end up being an oil-spraying mess, too.

Here's what the crankcase looked like after I'd drained 'everything' that would drain quickly, which is via a center-bottom drain that I added when I had it apart before (you can barely see the edge of the drain below the uptake screen, center).

The question on my mind is whether this glop wouldn't be there/ would not build up to any extent if I ONLY ventilate the crankcase better - or whether a more active 'intervention' is required, eg circulating it so it can sit and separate in a taller column with a manual bottom-drain, in the mold of a fuel/water separator.
 

Bobw

Diamond
Joined
Feb 8, 2005
Location
Hatch, NM Chile capital of the WORLD
I'd start by just ventilating it..

People have been running air compressors for a LONG time, and a lot of them never run
for very long, and I've never seen that kind of mess.

I've never had that kind of mess, and my compressor takes 5 minutes to fill up when its
empty, and then runs for 90 seconds, maybe a few times an hour. Granted today is
a humid day at 19%.. And we haven't had a drop of rain in 3 months.. The compressor
never really gets HOT, barely gets luke warm.
 

SVE Performance

Hot Rolled
Joined
Mar 21, 2007
Location
Milford,Ct
By keeping the oil hot there will never be a chance of the water building up so the amount of water in the crankcase at any time will be tiny. The engineers that designed the compressor never intended the crankcase to have that much water in it as they expected it to run for longer cycle times . By heating the oil, the vent system as desgined , will work as designed without having any detrimental effects to compressor life .
 

Strostkovy

Stainless
Joined
Oct 29, 2017
Water that evaporates from the oil is meant to be pulled into the head and be compressed with the rest of the air. The slight vacuum of the intake is beneficial to drying the oil. Do not be concerned about moisture entering the cylinders from the crank case. It is already there.

I think your only waste free option is to remove the oil, let it settle, drain off the water, and put it back into the compressor. Maybe heat it up externally. Otherwise you either need to change the oil, run the compressor enough to get it to operating temperature, or hope the water doesn't cause a bunch of rust.
 

tomjelly

Stainless
Joined
Aug 26, 2007
Location
GA
That water in the bottom of the crank case is normal for compressors in a lot of applications where they don't heat up. I think thats why they have such a deep sump, to avoid picking up the water- so the filter should definitely NOT have any of that sludge in it. The rusty sludge isn't normal. Maybe you have a bad check valve and the moisture in the air line is somehow getting back to the pump? After you find the source of the sludge if you want to keep after the water you could put an oil drain valve on and just decant off the water occasionally.
 

mmurray70

Hot Rolled
Joined
Jan 11, 2003
Quincy reciprocating compressor (model 340-33) that had fallen victim to unseen water-accumulation in the crankcase oil.
This compressor is essentially hobby-use, so it's never going to get run as these are 'recommended' to run.
Thats your problem for sure. I had similar problem with an over sized compressor that didnt run long enough. I called manufacturer and they explained that you always have some blowby and water gets past rings and into the base. They said it really needs to be run hard enough to get hot so the water will turn to steam and go out the crankcase breather.

If your compressor has plain bearings it might work just fine with some water in the base, not causing any major problems. Mine had Ball bearings, they rusted and then failed. I changed out the bearings and went with "RS" Rubber seal bearings to replace the open bearings. Been working fine ever since. Plain bearings are a better design for compressors IMO.

Some talk here about different oil as well. I've heard a lot of different theories but I stick with oils specifically designed for compressors because these will be designed to deal with the water and corrosion problems as much as possible.
 

metalmagpie

Titanium
Joined
May 22, 2006
Location
Seattle
Check your discharge valves. Maybe some hot wet air is escaping backwards into the cylinders thus allowing water to find its way back to the crankcase.

metalmagpie
 

ratbldr427

Stainless
Joined
Mar 21, 2006
Location
jacksonville,fl.
You may have excessive blow by which will make the problem worse. Don't know if its possible, depends on how your crankcase is made, but if you could run the air discharge line thru the c/case it would heat up the oil pdq. Or if it has an oil pump then plumb the oil line out side and around the intercooler or a small circulating pump that runs when the comp does or thermostat control might be easier. Sounds far out but just depends on.......
 








 
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