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Air bubbles in the oil........

Discussion in 'Compressors, Boosters and Blending Systems' started by widget, Oct 6, 2008.

  1. widget

    widget Manta Ray

    # of Dives:
    Location: South Africa
    707
    55
    28
    ............One of our Bauer compressors (K14) has started showing air bubbles in the oil sight glass, above the oil pressure regulator adjuster.

    I am assuming this is an indication that the final stage suction valve is finished, but before I go take it off line for repair, could there be any other fault (reason for this) I could check first?

    Oil pressure is still fine, but I have noticed a slight increase in oil usage, which leads me to think the floating piston and sleeve may need replacement as well.

    The unit has done roughly 900 hours since its last valve change, so its not bad going, but I was hoping for a bit more hours, Bauer recons a 1000 hours is usual for the final stage valves and I got a bit more on the previous set, maybe 1300 hours before it started popping the 3rd stage safety valve.

    We use the unit constantly, so I would rather make sure before I have to schlep it off for repairs, any ideas would be welcome.
     
  2. pescador775

    pescador775 Loggerhead Turtle

    2,652
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    0
    What type of oil and when was it changed? Sometimes, the Bauer oil pump needs to be deaireated after an oil change.
     
  3. widget

    widget Manta Ray

    # of Dives:
    Location: South Africa
    707
    55
    28
    Locally we use the SHELL CORENA P 150 oil which is approved by Bauer for use in their machines - it may have another trade name elsewhere, but unfortunately I am not aware of it.

    Pescador, the oil was changed about 200 hours back, I cant think the technician did any kind of deairation of the oil pump at the time, basically just changed the oil and reset the pressure into spec. I didnt see any bubbles before Saturday (three days ago) when I checked the unit, - there may have been, I just didnt see them, - but now its very obvious, and the oil looks slightly "frothy" in the sight glass after a few hours from start up.
     
  4. pescador775

    pescador775 Loggerhead Turtle

    2,652
    2
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    Check a small sample and observe whether the oil is milky. If blowby is aerating the oil then maybe water in present also. Has the output (cfm) and final psi been measured? That, along with blowby would be the definitive tests. Blowby should be about 8%-12% of output @ 3000 psi but I don't have the factory spec for your machine.

    Corena is a good oil.
     
  5. captain

    captain Captain

    6,726
    3,234
    113
    Is it possible it was overfilled and the oil is being aerated by being churned up by the crankshaft.
     
  6. CraigAClark

    CraigAClark Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: South Florida
    519
    21
    18
    I assume you are talking about during operation. Does the sight glass empty after shut down? What is the final shut off pressure and the oil pressure? Does the oil pressure fluctuate when running?

    There are several reasons why "blow-back" in the sight glass happens. Sometimes the final discharge valve is bad, or the oil pressure is too low for the final pressure. These are the simplest causes. The oil regulator could have a bad seat, the oil pump may be bad or the final piston and sleeve could be worn out. Indications from the oil pressure gauge and sight glass can direct you to the problem.

    I have seen this problem several times and it has turned out to be one or a combination of the above.

    Craig
     
  7. widget

    widget Manta Ray

    # of Dives:
    Location: South Africa
    707
    55
    28
    Thanks Craig, I will try and answer as best I can, maybe it will assist you to get a clearer picture.

    All the affirmatives first..........:D

    Yes, sure I was referring to "during operation" and on the sight glass issue, I have noticed it is emptying out on shut down quite quickly (which I thought a bit odd)............... and then, "Yup" there is a bit of fluctuation in oil pressure during operation which is also new, before, it was rock steady.

    Craig I am not quite sure what you mean by "final shut down pressure" could you maybe just help me out a bit there.?

    As I said, I am also experiencing a bit of extra oil usage, which lead me to think the floating piston and sleeve was "kaput"??

    How would I check on the oil pump seat Craig? Thats something I was not aware of before?

    The oil gets quite frothy in the sight glass whilst running, but I checked the oil in the sump and it dosnt appear to have moisture in it, at least I cant see any signs of it.

    Pescador...... Is there any way of checking "blow by" without that little gauge - (short of removing the head and sucking on the valve to see if it allows air through :D) ...........a kind of quick test??

    I really do appreciate all the assistance guys, I hope between us we can sort of nail it down to one or two causes I can tackle with the shortest downtime, besides, not only am I learning a bit more, but I find it very comforting to know there is a wealth of information willing to be shared amongst the members here.
     
  8. pescador775

    pescador775 Loggerhead Turtle

    2,652
    2
    0
    Final pressure refers to the set pressure for shut down. What pressure is it topping out, specifically, and moreover, what is the oil pressure doing at that point. Craig is possibly concerned about back flow of air from the fourth stage into the oil. The regulator is pretty simple. One should be able to unscrew the cap and inspect the innards. Mind the spring. You did say "fluctuation". Not much to go on but is a clue. He'll have to take it from here but the regulator could be at fault.
     
    Last edited: Oct 7, 2008
  9. CraigAClark

    CraigAClark Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: South Florida
    519
    21
    18
    Hey Widget,

    The fact that you are seeing the sight glass empty after shut-down is indicating to me that air is being "forced back" from the 4th stage. You say there is fluctuation in the oil pressure while running. Is it several hundred PSI or just a little?

    If your final pressure (shut-down) is 3500 psi, you can usually get away with 750 psi oil pressure. If your final is at 4500 psi you should set the oil pressure around 850-900 psi.

    Pesky will probably correct me on this as I don't know the specific terminology, but with the final piston and sleeve not having rings, the oil pressure acts as a seal, during compression, that prevents the air from "blowing Back". Normally, if the oil pressure is too low, the bubbles will not appear until your final pressure is in the range(s) I mentioned above.

    Now if the oil pressure fluctuation is several hundred PSI, then it is pretty certain that the oil pressure regulator is not holding adjustment. The oil pump is basically a diesel injector that only knows how to pump oil. The regulator is what controls the oil pressure. In my experience, I have never seen an oil pump fail, including machines that have been rebuilt after 5000 hours and are well into their second 5000 hours.

    Pesky, you mentioned about the oil pump needing to have the air relieved. The only time I have ever needed to do this is when the pressure doesn't come up immediately. The pump (injector) has basically lost prime. Most often this step, priming the injector, isn't necessary.

    Craig
     
  10. widget

    widget Manta Ray

    # of Dives:
    Location: South Africa
    707
    55
    28
    Okay, please correct me here if I am wrong, but if the air is been forced back from the 4th stage (as it appears because the sight glass definately empties) then its pretty sure the suction valve has gone?

    Our final pressure is at 4500 but I saw our oil pressure is a little less than 800psi - I will up it tomorrow and see if it helps.

    Oil pressure isnt fluctuating by that much Craig, maybe 50 Psi?? at the most, but before it was rock steady, no fluctuation at all.

    I agree on the final piston though Craig, and your comment makes sense because bubbles only appear at pressure, so its likely the sleeve is worn and allowing air back - its done roughly 1900 hours I saw on the log, so I think its pretty much at its limit anyway, dont you think?.

    I think your pointers are confirming my initial suspicion that the valves and floating piston are at their limit, and one if not both are failing, I am going to raise the oil presure tomorrow to 900 psi and see what happens.

    Just a last question, do you guys think its okay to run the unit like this? It runs on average, roughly 5-6 hours a day or more in tandem with another K14 as we are heavy users of air, I could shut it down if it will do damage, but then I fear the other one will have to run 10 -12 hours to keep up, which is also not that great I guess - my aim was to keep it running until Friday, when I can have it repaired over the weekend, but if you think it will just cause extra issues, I will just have to stop it.

    Thanks again for the help.
     

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