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  1. #1

    Pneumatic compressor issues

    I'm having some trouble with the air compressor controls in this building. I have two Square D pressure switches, a lead and a lag, that operate a Furnas alternating relay. The way this is wired is, the lead switch operates the alternating relay. The lag switch will help to take up slack, or, if the alternating relay fails to operate, will make both compressors run at the same time.

    Now, to the meat of the problem; as we near our pressure set point, the contacts on the lead pressure switch will begin to chatter. This, in turn, causes the alternating relay to chatter, which also causes the motors to both try to run. The pressure switch is not mounted directly on the tank, but on a device (see pics below) which also has the compressor discharge attached to it. What I would like to know is, could this device be allowing the pressure from the discharge of the compressor to affect the contacts of the pressure switch. Also, I haven't had a chance to explain all of this to my boss, so could any of you explain what this device is? I apologize for being long winded, but I want to provide as much info as possible to get the best response.

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  2. #2
    Bump

  3. #3
    Join Date
    Aug 2009
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    Prattville, Alabama
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    1,771
    Isaac, I don't have an answer to your question, but maybe this will help get the ball rolling here. As I read your post I was thinking it sounds like the pressure switch is getting weak and allowing the contacts to bounce as the pressure approaches setpoint. Then I looked at the pictures. I'm guessing that when you say "device", you're talking about that orange plastic looking thing. I've never seen one of those before. I've also never seen a pressure switch connected so close to the compressor discharge, either. I've always seen them connected to the tank. I wonder if that is to use the volume of the tank to dampen the pulsations of the compressor. And on this air compressor, the manufacturer, after deciding to mount the switch so close to the compressor, found that air pressure pulsations were a problem. And their solution was to use a dampener. Please note this is guesswork, with some assumptions built in. If that orange thing is a dampener, then the question becomes what is failing- the dampener or the pressure switch? Perhaps repiping the switch to another location, on the tank, would help. Try looking at the manual for this. If it's not available, try looking at their website for it.

  4. #4
    I doubt that the pressure switch is weak or failing; they are approximately a year old. A former employee changed both switches (lead and lag) around this time last year. Your assumptions of what is going on is exactly what I was thinking. I've always seen pressure switches mounted on the tank, and I do believe that the orange device is a damper of sort to reduce the pulsing of the compressor discharge. I ran my theory by my boss this morning, as well as showed him pictures, and he has never seen this type of device either. I'm going to recommend relocating the pressure switches and see where that gets us. I've tried looking at different compressor setups and components online, as well as going to a local compressor supply house, and I can't seem to find any info on exactly what this device is/does.

  5. #5
    Join Date
    Feb 2010
    Location
    Ontario Canada
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    1,339
    The orange thingy is just a manifold. It dampens out a little pulsation, provides for air cooling as well as putting the pressure relief and controls in one neat package.
    I would look at the pressure switch, you could have a weak spring causing the issues. Even if it is just a year old. Just my 2 cents.
    Never give up; Never surrender!

  6. #6
    You may be correct about the spring; but I feel changing the location will help. I quoted the job with using new pressure switches, so this should cover all of the potential issues at hand.

  7. #7
    Join Date
    Aug 2009
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    Prattville, Alabama
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    1,771
    Quote Originally Posted by trouble time View Post
    The orange thingy is just a manifold. It dampens out a little pulsation, provides for air cooling as well as putting the pressure relief and controls in one neat package.
    I would look at the pressure switch, you could have a weak spring causing the issues. Even if it is just a year old. Just my 2 cents.
    That's good to know. Now if I ever run across one, I'll know what it is. Thanks.

  8. #8
    Join Date
    Aug 2009
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    Prattville, Alabama
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    Quote Originally Posted by Isaac3384 View Post
    You may be correct about the spring; but I feel changing the location will help. I quoted the job with using new pressure switches, so this should cover all of the potential issues at hand.
    I would change location, too. Looks like you've got it covered.

  9. #9
    Agreed; I quoted new pressure switches installed off of the tank. Existing ports are to be plugged.

  10. #10
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    snipe70e, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

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  11. #11
    For those of you that may be curious about what happened with this, the engineer was skeptical that relocating the pressure switches to the tank would fix the issue. We ended up temporarily installing a new switch on the tank and wired it in to be the 'lead' switch. After a 4-5 month trial time, he was finally convinced and approved the work. Now, the lead and lag pressure switches sense the pressure from within the tank, instead of sensing the pressure from a manifold that is connected directly to the compressor discharge.

  12. #12
    Join Date
    Aug 2009
    Location
    Prattville, Alabama
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    Appreciate the update, Isaac. I believe you've made it better than it was when it left the factory.

  13. #13
    No problem. I know it has been a whole since I started this topic, but it may help someone else out along the way.

    I attempted to inspect the internals of the 'manifold', but that's almost impossible to do through a 1/4" FPT hole. Also, I ended up going with Hubble pressure switches instead of the Square D. When I first started working on pneumatic compressors I used the Square D switches, but I would get an occasional callback. Since I switched to the Hubbles, I haven't had a single callback.

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