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Replacing an oil flooded vane pump with a claw type pump

  • Friday, March 26, 2021 8:15 AM
    Message # 10237359
    Mathis Carlson (Administrator)

    For years, any time that I was involved in replacing an oil flooded vacuum system with claw type pumps I have always recommended also replacing the exhaust piping. I had been cautioned from various manufactures that the increased exhaust temperatures from the claw had a likely outcome of igniting all of the oil residue in the exhaust piping, resulting in a fire.
    I was talking with a few people this week and the topic came up again, so down the rabbit hole we went.
    We dug up a document from Busch that essentially said that continued use of an oil flooded pump has a higher risk of ignition in the exhaust line than switching to a higher temperature claw pump.

    Have I (and others) been using poor information for years?

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  • Monday, March 29, 2021 12:35 PM
    Reply # 10249439 on 10237359


    Good information! I'd never though of the accumulated oil mist as an issue.  Seems like mineral oil is ok.  Does synthetic oil have similar auto ignition temps?  Lots of pumps run synthetics to extend oil change durations.


  • Saturday, April 03, 2021 9:40 AM
    Reply # 10268827 on 10237359

    First, generally speaking, mineral oils have a lower "Flash Point" than synthetics, usually around 480-520F. Semi-syns (blends) slightly raise the Flash Point, and Full Synthetics can achieve temperatures of 620-650 F.  Now you can go down all manner of "rabbit holes" regarding silicon based synthetics vs di-ester based synthetics, additive packages, oil change intervals, and all sorts of nonsense. My advice is to eliminate the potential for the problem. I have not been able to use claw technology in my particular area due to altitude, less dense air, and the inability of that less dense air being able to remove the heat of compression as we move on the pump curve towards dead-head vacuum. Thus, our facilities are littered with burnt-up, dry technology pumps.  

    The following is from my 3-28-21 blog on website.

    We have been working on a device that monitors and mitigates high oxygen levels coming into the vacuum source equipment.  What we have found out is that oxygen levels in vacuum are not significant enough to cause, or sustain a fire.  It is the point of re-contraction of the gas (Ideal Gas Law, PV=nRT) that offers the perfect breeding ground for trouble. In fact, I would like to hear from anyone who has been involved in a hospital vacuum pump fire and ask them to describe what they found. My guess is that the pump housing chamber was found to be in good order, but the exhaust box/separator was trashed. We have been down all sorts of “goat trails” as to the cause of this: poor maintenance; electro-static charge; broken separator clips; improper oil (mineral base vs. synthetic, then silicon based synthetic vs. di-ester based synthetic, etc., etc).

      During the Covid pandemic, with the enormous addition of the amount of oxygen being evacuated into the vacuum piping, we have seen oxygen levels that go well beyond normal WAGD influences on the pumps. The solution is to mitigate the problem by diluting the gas to a point below the ignition level of the gas. This is not 23.6% of oxygen in the atmosphere, it is dependent upon the amount of oxygen molecules in that specific atmosphere. Case in point, why do we have a “tree line” in Colorado? The high mountains are noticeably void of trees above 11,300 ft. elevation. Too much snow? Too cold?  Is the oxygen concentration well below 20.9%?  No, it’s because the ambient air doesn’t contain enough oxygen molecules to sustain tree life. The same school of thought explains why Everest trekkers can’t get a fire started at base camp 5. Less dense air, means less oxygen molecules even though they are still comprise 20.9% of the atmosphere.

    I would love to hear from anyone regarding this subject. Data & knowledge are the solution.

    Scott Jussel

  • Sunday, April 04, 2021 12:26 PM
    Reply # 10271609 on 10237359

    Scott I agree with you on everything except trees need CO2 and give off oxygen but the density remains the same as you described.

  • Monday, April 05, 2021 4:11 PM
    Reply # 10276189 on 10237359
    Al Moon (Administrator)

    In my world its all about PARTIAL PRESSURE:

    Oxygen availability and altitude

    Although the percentage of oxygen in inspired air is constant at different altitudes, the fall in atmospheric pressure at higher altitude decreases the partial pressure of inspired oxygen and hence the driving pressure for gas exchange in the lungs. An ocean of air is present up to 9-10 000 m, where the troposphere ends and the stratosphere begins. The weight of air above us is responsible for the atmospheric pressure, which is normally about 100 kPa at sea level. This atmospheric pressure is the sum of the partial pressures of the constituent gases, oxygen and nitrogen, and also the partial pressure of water vapour (6.3 kPa at 37°C). As oxygen is 21% of dry air, the inspired oxygen pressure is 0.21×(100−6.3)=19.6 kPa at sea level. 

    Atmospheric pressure and inspired oxygen pressure fall roughly linearly with altitude to be 50% of the sea level value at 5500 m and only 30% of the sea level value at 8900 m (the height of the summit of Everest). A fall in inspired oxygen pressure reduces the driving pressure for gas exchange in the lungs and in turn produces a cascade of effects right down to the level of the mitochondria, the final destination of the oxygen.

  • Tuesday, June 29, 2021 7:46 PM
    Reply # 10712497 on 10237359

    What you state about the raw number of oxygen molecules in a vacuum atmosphere is true Scott.

    That is why the fires are in the exhaust box with residual gauge pressures of about 3 - 5 psig with lost of oil mist.

    The source of ignition still is a mystery though.

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