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banging hw recirculation system

bob young
bob young Member Posts: 2,177
maybe you could install a heatsink piping arrangement [27 " loop ] in lie of the banging check


  • chris_95
    chris_95 Member Posts: 47
    banging hw recirculation

    i have a 2yr. old home with a hot water recirculation line
    that "bangs" every time a hw tap is opened.
    the line is 1/2"having a laing circulator and swing-check before it tees into the cw make-up above the hw tank.
    the tank is indirectly fired via a quietside lo-temp boiler.
    the boiler drain on the hw tank is used to direct cooler water back to the quietside via a taco circulator. this is the reason the hw return line is not attached at the boiler drain location as it could fool the boiler and cause overheating. the hw tank's lower stat is used to call for
    heat by the boiler acting as the aqastat.
    the banging will also occur anytime the hw tank is being
    heated. interestingly there is no banging from any use of
    cold water thus eliminating water hammer.
    any thoughts or suggestions?
  • EJ hoffman
    EJ hoffman Member Posts: 126
    replace the swing check with a spring check

  • chris_95
    chris_95 Member Posts: 47

    ok. installed new spring-type check valve in place of the
    swing-type. immediately after the check i placed a
    type aa sioux chief captive air arrestor in line as well.
    bummer... still getting an occasional bang which is now
    intermittant rather than constant with faucet openings.
    the problem is definitely in the hwr cicuit, because if i
    valve it off, there is no banging.

    what else could generate a "hw valve opening" banging?
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,226

    ... the water hammer arrestor is part of the problem. Normally those go at the end of a line at the point of use. I'm trying to get a picture in my mind of what happens in your new setup when water is shut off. Another thought is that Nibco used to make spring checks with a rubber face. They were quiet.

    If there is a way to disable the arrestor, I'd try that first.

    Yours, Larry
  • EJ hoffman
    EJ hoffman Member Posts: 126
    Only banging with certain fixtures all all fixtures?

    What is the water pressure at the house? and do you have an expasion tank on the hot water side of the water heater? Is it set for the right pressure
  • Rich Kontny_3
    Rich Kontny_3 Member Posts: 562
    My Guess

    Would be similar to Larry's as I think water hydraulics are the suspects. Piping arrangements with long runs and flow restrictions can cause water hammer. Combine this with improper hangers or supports and you can get water hammer issues. Sourcing out the problem can be a little like looking for a needle in a haystack.

    Temperature differentials can also cause banging if extreme. The first thing I would do is try to similate the problem. Suddenly shutting of valves can cause water hammer. I usually find something obvious after the process of elimination exercise!
  • Plumdog_2
    Plumdog_2 Member Posts: 873

    He says the banging happens when OPENING the valves.
  • EJ hoffman
    EJ hoffman Member Posts: 126
    Expansion yes,but not for the noise

    I should have explained better. I was shooting down the next five questions without explaining or asking more questions. So banging water when valve opens with a swing check in the recirc, means water is rushing back against the swing check and banging shut. Fix replace the swing check with a spring check, softer close, but if this system has one swing check I assume it has 2 one also on the main. So being an enterprising young man I replace the other swing check also. But if it was a swing check on the main, maybe the original installer drilled the flapper thus allowing the hot water to back up through the cold main eliminating the need for an expansion tank,but if it was replaced with a spring check now we have exess pressure build up, so the next thread is help my T & P keeps blowing even after I replaced it 3 times.
    Here is another situation the Hammer arrestor is acting like an expansion tank, tiny but as the spring goes up from pressure a valve opens and wham the spring inside the hammer arrestor unleashes and slams back to original position causing a bang. That is if the hammer arrestor is spring loaded arrestor and not just an air chamber stub out.
  • chris_95
    chris_95 Member Posts: 47
    banging hwr circuit

    ok, i'm going to try this again... maybe i wasn't clear.
    i have a "banging" conditon when any HW valve is opened.
    no problems with either hw or cw valves CLOSING. the banging
    also occurs when the hw tank is calling for heat initially but not during the entire heating process.
    the hwr tees into the cw make-up of the hw storeage tank.
    (domestic hw produced indirectly with condensing boiler).
    just before the tee is a 1/2" ball valve, then the captive-air
    arrestor chamber, then a circulator and finally a tee into
    the hwr circuit which branches to reach both ends of the
    the spring check is a nibco with what appears to be a black
    neoprene seat.
    yes, there are 2 swing checks remaning, 1 in each branch
    about 6'-8' from the hwr circulator.
    finally, there is a ametrol captive air tank on the cw main
    about 15' from the hwr set-up and directly above the entrance. water pressure is 60psi (static).
    i think thats all the queries on the system.

    this is getting good, but please read my parameters closely.
  • EJ hoffman
    EJ hoffman Member Posts: 126
    replace all of the swing checks with spring checks

    and remove the hammer arrestor. And I bet you have a swing check somewhere in your boiler loop replace that also
  • chris_95
    chris_95 Member Posts: 47

    i thought you all might object to the 2 extra swing checks.
    i'm not convinced they're necessary anyway.off with their heads!
    there is no check valve in the boiler(heating section). i am
    absolutely convinced the problem originates with the hwr loop. if i valve it off, the banging is nonexistant!
    now, let's talk about how to get a nice,quiet hwr.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,226
    Those extra swing...

    ... checks are there to prevent ghost flow? You could open them up and remove the discs. If ghost flow doesn't happen, leave the discs out. If it does happen, bigger guns (heat trap, spring check, flow check...) are needed.

    Another thought would be running the recirc line to a properly valved drain on the tank rather than to the cold supply. That would separate those things hydraulically-wise.

    As you probably can tell, I'm still confused about the system design. DHW normally doesn't need multiple check valves. It sounds more like a heating system. A picture or diagram would be nice :~)

    Yours, Larry
  • chris_95
    chris_95 Member Posts: 47

    this is an indirect-fired hw storage tank which is
    heated by the domestic heat exchanger in a quietside qvm-125
    lo-temp boiler. a taco 007 is used to draw cooler water off
    the bottom of the storage tank and return to the heat exchanger. when the storage tank calls for heat, the tank's acquastat turns on the taco which in turn closes a flow
    switch at the quietside heat exchanger, and begins the heating cycle. this circuit is completely seperate from the
    heating section of the boiler. once domestic hw is up to temp., the quietside shuts down.
    this long-winded explanation reveals why the hwr isn't
    connected to the boiler drain tapping. i feel it would "fool" the quietside into continually firing because
    of the flow induced by the circulator in the hwr circuit.

    here is description of the hwr circuit:
    -the circuit begins(or ends) at a tee on the cw make-up to the hw storeage tank.
    -next in line is a ball valve to isolate the hwr from the
    domestic system.
    -a captive air hammer arrestor was placed next
    -a spring-type check valve was installed and the swing-type
    -a laing 1/150hp circulator is used for recirculation
    -after the circulator piping a tee provides for 2 seperate
    hwr branches extending to both ends of the house and terminate at the hw supply at the furthest fixtures. this forms
    the 2 recirc lines for the circuit. swing type checks are
    on each branch just after the tee adjacent to the hwr circulator.
    the banging only occurs when a hw tap is opened. it also
    occurs occassionally when the hw storeage tanks call for
    heat, but not consistently.
    water hammer is not present on the cw side.system pressure
    is 60psi. expansion tank on cw supply to system.
    sorry, my scanner is busted and i've not found a similar
    layout on the net as of yet. if i do i'll post
    hopefully my explanation will clarify.
    today, i'm removing the hammer arrestor and observe the effects. not sure about opening the 2 swing checks.they
    may have mineral deposits not conducive to removal. i may
    have to take them out of the circuit entirely.
    the game is afoot!
  • chris_95
    chris_95 Member Posts: 47

    i found the problem. first i removed the hammer arrestor.
    no change.
    next i removed 1 of the swing checks on the branch hwr and
    valved off the other branch.turned the hwr back on and
    lo and behold, no banging!
    removed the swing check on the other branch and amazingly
    no banging.
    it was the damn swing checks all along. problem solved.
    i want to thank all of you who took time to answer my queries.
    much appreciated.
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