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Trouble with school air compressors getting water in crankcase

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  • Trouble with school air compressors getting water in crankcase

    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?
    Last edited by winchman; 12-14-2010, 02:47 PM.
    Any products mentioned in my posts have been endorsed by their manufacturer.

  • #2
    humidity

    Originally posted by winchman
    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.

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    • #3
      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.

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      • #4
        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.
        Last edited by Don Young; 12-14-2010, 09:23 PM.
        Don Young

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        • #5
          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.
          Any products mentioned in my posts have been endorsed by their manufacturer.

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          • #6
            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.
            Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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            • #7
              Originally posted by winchman
              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?
              Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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              • #8
                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.
                Any products mentioned in my posts have been endorsed by their manufacturer.

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                • #9
                  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.
                  Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                  • #10
                    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. :-)

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                    • #11
                      Thinking out loud

                      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

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                      • #12
                        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.
                        Any products mentioned in my posts have been endorsed by their manufacturer.

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                        • #13
                          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.
                          Byron Boucher
                          Burnet, TX

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                          • #14
                            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.
                            James Kilroy

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                            • #15
                              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/art...ing_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.
                              Last edited by Willy; 12-16-2010, 12:00 AM.
                              Home, down in the valley behind the Red Angus
                              Bad Decisions Make Good Stories​

                              Location: British Columbia

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