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winchman
12-14-2010, 02:45 PM
During the past year, two of the large shop air compressors at the school had to be replaced because moisture kept collecting in the compressor crankcase, and it eventually ruined the bearings. Both compressors were outside, but in reasonably well-protected locations. Both were three-phase units with twin cylinder two-stage compressors and ten horsepower motors, but they came from different companies.

In both cases, the problems started as soon as the compressors were installed several years ago. The oil in the CC would turn milky after a week or so of use. They installed CC heaters and automatic tank drains, but that didn't help. They did change the oil fairly often, but apparently not often enough to prevent damage to the bearings.

So, what's the best way to keep moisture from collecting in the compressor crankcases?

vincemulhollon
12-14-2010, 03:26 PM
During the past year, two of the large shop air compressors at the school had to be replaced because moisture kept collecting in the compressor crankcase, and it eventually ruined the bearings.

If its a high outdoor humidity thing, pipe your intake air from the dehumidified air conditioned inside of the school. Insane as it sounds, it'll work.

CCWKen
12-14-2010, 03:29 PM
Sounds like they're not used enough. Are they connected in parallel or service different areas. They need to run long enough to heat the oil HOT. Moisture in the CC would normally be evaporated through the vent during the run cycle(s). Also, check the CC vent to make sure it's clean and open.

Don Young
12-14-2010, 09:20 PM
Another easily overlooked cause of the problem might be inadequate crankcase ventilation. Many crankcases get moisture/water in them but it is vaporized by the heat and passes out the vent. If the crankcase is warmer than the atmosphere and well ventilated it should not develop water problems. If you try to keep the crankcase sealed up it will likely make the problem worse as any blowby will contain water vapor.

Edit: I see CCWKen has the same basic suggestions.

winchman
12-15-2010, 02:34 AM
The thing that really puzzles me is there is a third compressor that's very similar to the other two in a similar location behind the welding shop. It collects lots of water in the tank, and it gets drained regularly, just like the other two. There's no CC heater on it.

It's been running without CC moisture problems for at least ten years, though.

Black_Moons
12-15-2010, 05:27 AM
I agree with CCWKen, Its likey because the welding shop actualy USES thier compressor, Where as everyone else is just using it to run some blow off guns or something.

Have the other compressors replaced with 5 or even 2 HP units next time if they are not running down the 10hp compressor. Maybe keep the old tank and just buy a new compressor and motor, Or plumb the new compressor into the old tank for extra storage. If the compressor never gets 'hot*' in use, Its not being used enough.

Hot*: As in, Can not hold hand on it, Idealy can not even touch the thing. Compressors are designed to get HOT. The air discharge line can get hot enough to boil water.

camdigger
12-15-2010, 07:11 AM
The thing that really puzzles me is there is a third compressor that's very similar to the other two in a similar location behind the welding shop. It collects lots of water in the tank, and it gets drained regularly, just like the other two. There's no CC heater on it.

It's been running without CC moisture problems for at least ten years, though.

Are the compressors the same make and model? What might be different about how the compressors are made?

What kind of differences are there in the use/work cycles?

winchman
12-15-2010, 10:04 AM
Probably the biggest difference is that the welding shop is MUCH older than the other two shops, and the pipes leak enough so the compressor runs five minutes every hour or so just to keep up with the leakage. It also runs at a higher pressure, and I'm sure that helps to heat the CC.

The compressors in the other two shops are probably sized for the max demand instead of the average usage they actually see.

Why do you suppose the CC heater didn't work? They were installed by the company reps shortly after they started having problems. You'd think they'd know how to get that right.

Black_Moons
12-15-2010, 10:29 AM
Id say the CC heaters don't work well because they only keep the compressor warm, Not hot. a 10HP compressor is likey disipating a few thousand watts of heat easy in operation, that heater is likey a few hundred watts.

You could probley solve the problem by just installing a timer + air solanoid valve. Have the compressor blow off and run for an hour every day or even week.

For bonus, it could be connected to the tank drain.. :) If you don't mind replaceing/fixing the solanoid now and then due to crud lodged in it.

Lew Hartswick
12-15-2010, 11:53 AM
Crank case heaters are intended to keep the thing warm enough to start in winter not to get rid of moisture in the oil.
...lew... who has used them on Air Conditioing equipment on roof tops. :-)

Guido
12-15-2010, 01:38 PM
The highschool must be a large SOB, to require three nice air compressors. If one is healthy and getting used often, and two are failing due to watery oil in the cc, (and little useage) then there's the answer.

We have to wonder what happened to the two machines which were replaced? Repaired and sold as used, or simply hauled away never to be seen again? Just wondering----------

--G

winchman
12-15-2010, 02:23 PM
It's a technical college with welding, automotive, and agricultural equipment maintenance programs.

One of the compressors was hauled away when the replacement was delivered, the other is still sitting there.

Thanks, that makes sense about the CC heaters. I was thinking you'd keep the moisture out just by keeping the oil above ambient temperature, but obviously that's not enough.

Boucher
12-15-2010, 10:05 PM
I would recommend using a 30 wt. synthetic compressor oil. Moisture in the cc ties up the anti foaming agents in the older compressor oils and results in a lubrication break down. If oil is stored in 5 gal cans it can get contaminated in the can if not stored in a dry location.

jkilroy
12-15-2010, 10:24 PM
I would rig up the pair such that both tanks are connected then run one compressor, maybe alternate every other week or so. If you get in a real high demand period turn both on, but one running by itself will run a lot more and get to a reasonable running temp. I have got a 10hp three phase unit myself but I have been thinking about adding a second compressor, probably a 5hp, to the same system, then staggering the pressure settings such that the big unit only kicks on when the system is really low on pressure.

Willy
12-15-2010, 11:29 PM
I think we can all agree that the compressors are not working long and hard enough to build up sufficient heat in order for the accumulated crankcase moisture to evaporate.
One method I have used in the past on a large compressor that only saw occasional brief operation during cool weather was to vent the crankcase into a large closed reservoir so that it could vent but it would breath essentially the same air repeatedly. This would ensure that the compressor was not taking on ambient moisture laden air on each stroke.

I also like Jkilroy's suggestion, it would be easy to incorporate and would make the system work more efficiently and build up temperatures in one unit much quicker and put less hours on the other unit.

I'm not sure what the ambient operating temperatures are or the amount of time each unit runs per hour, but if no changes are done to the system oil change intervals must be drastically increased in order to drain accumulated moisture from the sumps...irregardless of oil type, conventional or synthetic.
Below is a quote from a site dealing with plant maintenance regarding rotary screw compressors.
Although I don't believe you are using rotary screw compressors the principle remains the same.


http://www.plant-maintenance.com/articles/rotary_compressor_winterizing_tips.shtml







A quality synthetic oil will flow better at low temperatures than a petroleum based oil with the same viscosity. However, cold temperatures can still have a negative impact on a compressor with synthetic oil.
The real threat to the oil is the accumulation of water in the oil sump. The source of the liquid is condensation which happens when a rotary screw compressor operates under 140 degrees F.
The water from condensation is boiled off and moved out of the compressor during warm weather. This contamination is passed out with the compressed air flow and will be removed at the aftercooler and other locations.
The water contamination will settle in the oil sump during cold weather conditions. This is a threat because a small amount of water in the oil will accelerate bearing wear and corrosion regardless of the type of oil. Water will separate from the oil if the compressor is shut down at the end of the work day. This is why compressor manufacturers recommend draining a small amount of lubricant on a regular basis during cold weather to check for water before starting the compressor.


Edited for spelling.

Orrin
12-16-2010, 01:07 AM
I worked at an installation where we must have had dozens of compressors. The ones that saw little use always got water in the crankcase oil during the wet, high-humidity season. In the dry summer months they were all right.

But, some people never could make the connection. Every year when the humidity shot up the worry-warts started having spasms, wondering what was wrong with the compressors. They never did catch on.

Orrin

Richard-TX
12-16-2010, 01:20 AM
What Orrin said.

Instead of having the compressors outside sucking in 88% RH air why not bring them inside so they compress relatively dry air?

winchman
12-16-2010, 12:58 PM
The noise of the compressor would be a problem in a teaching situation. They don't want to pipe the CC vents and air intakes to the air-conditioned classrooms for the same reason.

airsmith282
12-16-2010, 04:25 PM
the simple soloution being the dam things indoors where they belong, compressors are not designed to be setup outdoors. now if you heated the place they are in and are able to keep the temp to min of room temp then you wont have the problems your having,

Willy
12-16-2010, 05:06 PM
So, what's the best way to keep moisture from collecting in the compressor crankcases?

If they choose not to implement any of the alternatives presented here, then the answer is obvious...drain the compressors more often, weekly if that's what it takes.
One has to weigh the price of monitoring and changing the oil during cool damp weather vs. new compressors every few years.
It's that simple, the choice is theirs.

Lew Hartswick
12-16-2010, 05:16 PM
The noise of the compressor would be a problem in a teaching situation. They don't want to pipe the CC vents and air intakes to the air-conditioned classrooms for the same reason.
It certainly would not make a bit difference in the metal shop here.
You wouldn't be able to hear it over the BANGING of the welders
chipping slag. :-) My ears are still ringing after an hour or so. :-(
...lew...

justanengineer
12-16-2010, 05:29 PM
Most of the schools I have seen that have centralized compressors have them located in a boiler room where its typically pretty hot, dry, and noisy already anyway due to circulating fans. The only problem Ive ever heard of in these installations was from the condensation sitting in lines that go to labs/rooms that dont regularly need the air. In that case the only maintenance required is to send someone around every few months to open the room valve for a second to blast out the condensation.

Black_Moons
12-16-2010, 09:54 PM
Lew Hartswick: Tell them to switch from flux core to gas mig welders.

Problem solved!.. Unless they are using that double shielded stuff. Then tell them to go back to regular mig wire and just clean up the metal first :)

winchman
12-17-2010, 04:15 AM
The welding shop isn't air conditioned, and the compressor outside is doing just fine. I wear my earplugs whenever I'm in the welding shop, and put on my earmuffs whenever I use a grinder.

The other shops are fairly quiet and comfortably air conditioned.

I think we've pretty much covered what's causing the problem with the moisture in the compressors....not being used enough to heat the oil and outside high humidity. I doubt they'll do anything to change either situation.

airsmith282
12-17-2010, 07:07 AM
The welding shop isn't air conditioned, and the compressor outside is doing just fine. I wear my earplugs whenever I'm in the welding shop, and put on my earmuffs whenever I use a grinder.

The other shops are fairly quiet and comfortably air conditioned.

I think we've pretty much covered what's causing the problem with the moisture in the compressors....not being used enough to heat the oil and outside high humidity. I doubt they'll do anything to change either situation.

not being used enough to heat the oil sorry but i dont agree,there at all, my shop is heated and so is my basment and my compressor does see some use but not alot, i have changed the oil once sence i got it 2 years ago thats how often i use it, the most use its seen is when sand blasting and that has only been like 3 times max so far, this winter its been used a bit so the shop door left open heat in the shop shut down noe sence wasinting heat my main hose lives out side, and was working most of the day in the 12x20x8 tent garage and have alot so far this winter not just on cars and still my oil is good ,, and once that milky crap starts on you , you have to flush everything clean until its all gone or it just comes back , eventully you will blow the compressor, then you will have ice billl to fix it, lack of use is not the problem,, its gotten contaminated and its not going clear even with a 100 oil changes , its has to be flush out totaly might even need to be taken apart and properly cleaned thenput back togeter, and then put proper heat where its stored or move it indoors and keep it at a constante temp of at least room temp, higher temps wont hurt it, my shop temp where it is not is usualy 25 degrees at alll times so its pretty freaking hot in there all the time, and summer time is worse for the heat , and its a bit humid as well.