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Gas reg pulsing

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metrosilo
metrosilo Member Posts: 37
in Gas Heating

Hey everyone

I have an odd problem. I’m working in a commercial building. 10lb gas coming in.
I have 3 sets of boilers in a boiler room and they each have their own regulator. So 3 regs in total. When one or more are firing, the regulator pulses. Almost like hunting. But what’s odd is that all three do it.

Another thing that’s happening is when I take the cap off, it really starts to pulse.
All three regs do this.
however, when I remove the union for the regulator vent, it just pulses like normal.

Regulators are 10lbs to 7-20”


anyone have any experience with a problem like this?

IMG_7881.jpeg IMG_7882.jpeg

Comments

  • pecmsg
    pecmsg Member Posts: 7,074

    Is that the correct regulator?

    67f575b7ed4ac064da0bde19_NGR06Lit-2025v03.pdf

  • GGross
    GGross Member Posts: 1,906

    when you say pulsing are you seeing inconsistent gas pressure? and if so have you measured that? What was the problem that got you called out? how long has this exact setup been installed (boilers and regs) can you take pictures of the complete gas train and boilers?

  • metrosilo
    metrosilo Member Posts: 37

    gas pressure is consistent.
    you can hear the regulator pulsing.
    when you remove the cap, you can see the rod moving up and down and the regulator starts shaking. (This happens to all the regulators).
    One reg going to two Raypak 1,500,000 each

    One reg going to two Paterson Kelley. 2,000,000 each

    One reg going to one Paterson Kelley. 2,000,000

    Building started out with the single PK. The they added the two Raypak and now they added the other 2 PK. These are all on separate boilers systems (piping)


    gas trains are what is on each boiler. I don’t think that’s the problem.

  • Jamie Hall
    Jamie Hall Member Posts: 27,391

    Do they pulse in unison? Or are they out of phase with each other? And have yu — I assume you have — watched the gas feed pressure — not output, input — just upstream of each regulator? What I suspect is happening is that the gas pressure just upstream drops slightly, the regulator opens to maintain gas pressure downstream (and probably does), but this causes the gas pressure upstream to drop a little more, which in turn causes another regulator to pen slightly — by which time the regulator you were watching sees a slightly higher gas pressure and closes slightly…

    Rinse and repeat. I confess — freely! — that I have not seen this with gas — but I have seen it with pressure reducing valves on water supply systems, but it takes a close eye to see it in the pressure variations.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JUGHNE
    JUGHNE Member Posts: 11,552

    Do the 3 regs have a common vent pipe to the outside?

    Could that piping be plugged?

    Don't want to blow air thru any piping if any still connected to the regs.

    mattmia2
  • metrosilo
    metrosilo Member Posts: 37

    in my original message, when I take the cap off the back, the reg goes crazy. Pulses a lot and the rod bounces around. With the cap on but the vent piping open, nothing happens. Just the same minor pulsing I’m trying to figure out.

  • JUGHNE
    JUGHNE Member Posts: 11,552

    Your common vent pipe, if you have one, could be plugged outside.

    Thru the roof or wall.

  • ratio
    ratio Member Posts: 4,240

    "Cap off the back" means the li'l plastic cap that covers the pressure adjustment? Sounds like the vent(s) might be restricted.

    You may want to verify the orifice sizes too. There may be some overlap in the volume, maybe try the next size down if it is large enough.

    Did this start recently?

  • mattmia2
    mattmia2 Member Posts: 16,844

    If the appliance regulators have vent restrictors instead of outside vents make sure those didn't suck up some sort of dust and get plugged.

  • Bob Harper
    Bob Harper Member Posts: 1,166

    I've had this before. Where you have a common vent, it must be sized properly to handle all 3 simultaneously. Even where sizing charts indicate proper sizing, it may be insufficient due to fittings, pipe runs, termination, etc. This is very simple to diagnose: disconnect the vent piping at that ground union then fire them up. If it pulses you have a bad regulator- blown diaphragm, restricted orifice, etc. If the reg. is ok, reconnect the piping so just one boiler. If it starts pulsing, it's way undersized/ restricted. If not, add on the second and so on until it replicates the phenomenon.

    If they are not common vented, they each may be undersized/ restricted.

    The upstream regulator may be problematic and not this reg. Contact the utility if need be. Sometimes, putting in a buffer section downstream of a misbehaving regulator can allow it to settle down before hitting the reduced near piping at the appliance. Just increase the piping about a foot or two downstream of the regulator 50 to 100% for about 6 Lf then back down. This is actually required with some generators.

    FYI, the regulators shown are piped incorrectly. The code requires a shutoff immediately upstream, a sediment trap and ground union upstream to protect the reg. while providing a suitable attachment of a psi gauge and means to disconnect the reg. if replacement/ service required. Downstream a low-pressure tap is also required. HTH.

    Let us know what corrects it.

    bburd
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 20,206

    MA does not allow common venting of regulators for that reason. You also need to check with the reg manufacturer for sizing assistance. If the regs are "hunting" you have to size them based on gas pressure in gas pressure out and cu feet of gas (load). A mismatch will drive the regs crazy.

  • ratio
    ratio Member Posts: 4,240

    The more I look at that 1st picture, the more confused I get. A dirt leg with a ball valve on the inlet to the regulator? A dirt leg (with no ball valve this time) on the vent line??

  • Bob Harper
    Bob Harper Member Posts: 1,166

    Re-read my post- The gas code REQUIRES a shutoff immediately upstream of any Medium Pressure regulator plus a sediment trap to protect the reg. plus a ground union to disconnect the valve, trap, union, or regulator. Downstream you need a means of attaching a manometer for wci or psi gauge for psi.

    If the vent turns upwards, you need a trap so it does not become blocked from condensation, dirt, etc.

    MA's plumbing code is definitely unique and the plumbers who write it are very powerful.

    We've had to change brands/ types of regs. on higher volume systems. For instance, a Maxitrol 325-7 simply could not settle down even with just one appliance, located and vented directly outdoors with a 6 ft. buffer leg.

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