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  1. #1
    Join Date
    Jun 2004
    Location
    MidWest
    Posts
    64

    Confused

    For any of those that work on rapid air systems. I normally do not work on these and have come across a problem I can only guess at. I have a MAU system w/ 6 or 7 burners. Cust. says they shut it down due to it producing 50 ppm intermitantly. They have not seen what the burners were doing while it had this problem. I looked at it and cycled the thing at least 30 times in high and low fire. I can only get it to produce about 9 to 15ppm and the burners light fine. It has 2 honeywell fluid valves, a maxitrol high and low fire gas valve, and air stream switch, variable dampers, and a pilot valve. I have plenty of gas going to the unit and 2" on high fire. Only thing I can come up with is that this unit is an a area where semi's pull in and out of on a somewhat regular basis and the intake for it is right out side a roll up door which the unit is right on the other side. Maybe it is pulling in exhaust? What are your thoughts on it? Thanks.

  2. #2
    Join Date
    May 2004
    Posts
    12,268
    It is hard to say without seeing it RJ

    I assume it is nat gas and you said you have checked out the burners, igniters and safeties. You sound like you know what you are doing but you didn’t say if you checked the gas pressure to specs and if the regulator is in good shape and can breathe. I am sure the HX is in good shape too and that you checked the burner draft.

    You know that Aldehyde and CO gas are bi products of unburned gas. Nat gas outside a range of 4 to 14% gas to air mixture, dirt interfering with primary air flow mixture, lack of secondary air and so on will do the same. Flame impinging on a cold surface will also cause soot.

    If you have already removed the basics out of the equation then the answer is the most obvious cause(s).

  3. #3
    Join Date
    Jun 2004
    Location
    MidWest
    Posts
    64
    talking about flame impingement I did find 4 2" hairline cracks on 4 different burner flanges. But I did not think it was enough to cause this problem 1 day and then not for 3 to 4 days.

  4. #4
    Join Date
    May 2004
    Posts
    12,268
    Did you inspect the combustion heat exchanger for cracks?

    If the burners have over heated to stress stage then it is possible there is a stress fracture in the HX. Could be caused by overfire or just old age, like me.

    I still don't think this is your problem but all basics have to be covered before you go looking outside the unit itself.

    Cover the basics and uncover the problem, if you know what I mean. Smack it, bang on it, kick it, spit at it and cuss it if you have to and it will reviel itself.

    You wanted other thoughts; I hope this will point you in a good direction.

  5. #5
    Join Date
    Jun 2004
    Location
    MidWest
    Posts
    64
    I forgot to mention it is direct fire.

  6. #6
    Join Date
    Aug 2002
    Location
    manitowoc wisconsin
    Posts
    4,943
    Sorry I have worked mostly on weatherite mua units.I ran into this a few times with weatherite's when the burners needed pulled & orifices redrilled.
    Take your time & do it right!

  7. #7
    Join Date
    May 2004
    Posts
    12,268

  8. #8
    Join Date
    Sep 2002
    Location
    Deer Trail, CO
    Posts
    216
    If you can find a manual on the burner assembly you'll find a section on setting up the bypass air dampers on the burners. Direct fire burners of this type do generally run with something of a high CO level being rather inefficient as they are. Having a direct fire MAU means you HAVE to have some form of exhaust system in circuit with the unit for proper ventilation.
    Don't let your ego get in the way of a good decision

  9. #9
    Join Date
    Jun 2004
    Location
    MidWest
    Posts
    64
    The burner orifices had been cleaned and drilled by the maintenance crew which I looked at and they looked clean w/ no rust.

  10. #10
    Join Date
    Jul 2004
    Location
    Virginia
    Posts
    3

    Combustion Air

    Did you check the combustion air? Is it enough? Is there another appliance that comes on and pulls a negative pressure on the building which will affect the combustion air?

  11. #11
    Join Date
    Jun 2001
    Location
    Northwest Indiana
    Posts
    1,312
    Unless the earth goes negative, I do not think this unit will suffer from combustion air problems.
    If that unit is reburning exhaust from the trucks(alot of exhaust), Your alarm probably is going to ring out.
    Where is the co sensor located??? These units move a ton of air, they would most like dilute the truck exhaust before it becomes a problem. Unless it is a significant amount. Typically in industrial applications, once you start monitoring co, you'll usually find you always have elevated levels at some point(intermittantly) througout each day. Thats why I don't see alot of alrms out there. Usually if there is detection being used, there will be a large inter-locked fan to exhaust the space to back safe levels once the alarm triggers it. Sounds to me like there is a tree hugger running that account of yours and just complicating the unavoidable results of industry("intermittantly"). This is a perfect opportunity for you to sell him that needed exhaust system.
    Good Luck
    Bernie
    If you cant fix it right, try again.

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