Pressure regulator install for water hammer

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by boaterbill, May 1, 2013.

  1. boaterbill

    boaterbill New Member

    Messages:
    10
    Location:
    ne ohio
    Background info:
    Water dept says they deliver 80 psi. Turning off all cold water faucets quickly, fluidmaster 400 toilet valve and washing machine cause hammer. I
    have a Bosch on demand gas tank-less water heater. Water meter located in utility room, mount vertically 2' above concrete floor with 60 year
    old shutoff valve below it. Shutoff valve does not fully stop water flow, while closed fine stream of water coming out. Water department shutoff
    4 feet below ground somewhere in the yard.

    The Plan:
    Close in house shutoff valve ( fine stream of water still flows in closed position) best I can and install threaded 1" ball valve on out flow threaded
    nipple to become working shutoff valve. There is a floor drain 2 feet away. From this point continue on to install PRV. Since I have tank-less
    water heater would I still need an expansion tank? Would this stop the water hammer?

    Would lowering the water pressure affect the operation of the tank-less WH?

    Thanks in advance. All comments welcome.

    Boater Bill NE Ohio
    Last edited by a moderator: May 3, 2013
  2. DonL

    DonL Out of the Trades

    Messages:
    3,910
    Location:
    Houston, TX
    "would I still need an expansion tank?"

    I would say Yes, to do it properly.
    Last edited: May 1, 2013
  3. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,328
    Location:
    Yakima WA
    Yes for sure on the expansion tank. The PRV will create a "closed" system which means when the water heater does its thing, the water will expand and have no place to go. The result will mean the T/P on the water heater will open every time the water heater is on. 80 psi is on the high end of acceptable, and is quite a bit higher than necessary. I have no words of wisdom on the tankless water heater, but I would guess that 50 to 60 psi would be plenty.
  4. boaterbill

    boaterbill New Member

    Messages:
    10
    Location:
    ne ohio
    I should add that I will be using the Watts 25AUB-Z3 which has a bypass valve to allow for expansion back into the line. Would I still need the expansion tank with the PRV having this feature?
  5. Jerome2877

    Jerome2877 In the Trades

    Messages:
    397
    Location:
    BC
    No, you would NOT need an expansion tank!

    The on demand water heater only heats the water when it has water flowing through it and when the flow stops it shuts down. Then the heated water that is still in the pipes will cool so the pressure would never increase past whatever the PRV is set to.
  6. DonL

    DonL Out of the Trades

    Messages:
    3,910
    Location:
    Houston, TX

    Water Hammer can work on Hot and Cold water.

    What is your theory to back up your claim ?


    I guess I may not understand.
  7. Jerome2877

    Jerome2877 In the Trades

    Messages:
    397
    Location:
    BC
    I am talking about thermal expansion and the lack of it in an on demand water heater.

    Water hammer is caused by water stopping quickly in the pipe and is best controlled with a schock arrestor as close as possible to the end of the run. Sometimes a PRV will help stop or lesson this but an expansion tank is not designed for stopping water hammer.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,486
    Location:
    Cave Creek, Arizona
    quote; The PRV will create a "closed" system which means when the water heater does its thing, the water will expand and have no place to go.

    When water is flowing there is no "closed system", and since the water heater only operates when water is flowing, thermal expansion is not possible and thus an expansion tank is not needed. HOWEVER, an expansion tank, which is just a very large "shock arrestor", MAY absorb pressure spikes from turning off faucets too quickly, depending on where it is installed. A PRV may NOT stop the water hammer unless your pressure is set so low that it is unacceptable.
  9. boaterbill

    boaterbill New Member

    Messages:
    10
    Location:
    ne ohio
    Thanks for the response and thanks to all that have posted.

    I'm dealing with a 65 year old copper supply system which has been very trouble free. This is a post WW2 little spec.veterans home, may be 650 sq. ft. on a slab; 1 bath and kitchen. All exposed plumbing is in utility room 5' x 12'; furnace, washer, dryer, utility sink, tank-less WH are all in here. It's between kitchen and bathroom. I cannot afford any major plumbing failures or it would destroy everything on the ground floor.

    I agree that if PRV is installed it may not stop the water hammer. The water hammer now will trip the tank-less WH safety valve. The Fluidmaster tank valve seems to trigger this when the toilet tank valve stops filling. I have the tank valve barely open to stop this.

    I think the expansion tank will arrest the hammer as you suggest but would it just create a link in the system that will fail in time and flood the house? Would small arrestors at each delivery point be more fail safe in the long term? Just looking for some long term peace of mind.
  10. DonL

    DonL Out of the Trades

    Messages:
    3,910
    Location:
    Houston, TX
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,486
    Location:
    Cave Creek, Arizona
    Individual arrestors, when they work, will ALWAYS be better because you can install them at the "hammer causing" locations. One central "arrestor", or expansion tank, MIGHT do it, since most of your plumbing seems to be localized, but there is no guarantee.
  12. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    3,897
    Location:
    NW Ontario, Canada
    Yes, at the end of the line is where they do the most good. Water cannot be compressed so consider the line of water as being a mass with inertia. The gas inside the arrestor compresses and works like an airbag, absorbing the impact.
  13. DonL

    DonL Out of the Trades

    Messages:
    3,910
    Location:
    Houston, TX
    You can build a arrestor using a Piece of PVC pipe and a T and a end cap.

    But when it gets waterlogged you have to drain the water out of it.


    You may need a special permit to buy PVC pipe and end caps at the same time, now a days.
  14. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,486
    Location:
    Cave Creek, Arizona
    quote; But when it gets waterlogged you have to drain the water out of it.

    Good luck "draining the water out of it", unless the entire system was set up with that in mind.
  15. boaterbill

    boaterbill New Member

    Messages:
    10
    Location:
    ne ohio
    I picked up a water pressure gage and the water pressure is 80 psi. When cold water is turned off at all locations it jumps to 140 psi. The hammer noise is coming from inside the tank-less water heater. If I shut off cold water valve to the tank-less water heater all is quiet.

    I'm thinking my only solution would be as Gary Swart and hj suggested, PRV and the expansion tank. What about PRV first and see what happens, then add expansion tank? Placing expansion tank may be a problem. Could I place it 10' away and still be beneficial for water hammer?

    Will the banging inside the tank-less destroy it?
  16. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,486
    Location:
    Cave Creek, Arizona
    If the water pressure is 80 psi, the pressure regulator would be useless. The 140 psi is being generated inside your system which would be after any PRV you install. The expansion tank, in this case really an "accumulator" would act as a buffer, but since any hammer arrestor works best when it is RIGHT at the source of the hammer, not where you hear it, you will not know if it works until after you install it.
  17. boaterbill

    boaterbill New Member

    Messages:
    10
    Location:
    ne ohio
    Thanks hj,

    Tomorrow I will install hammer arrestor at fill valve on the toilet and another at the front loading washing machine. These two items seem to generate the biggest shock through the system. I'll post the results.
  18. boaterbill

    boaterbill New Member

    Messages:
    10
    Location:
    ne ohio
    I installed Sioux chief arresters at front loader washer and fluidmaster fill valve. After install water hammer was muffled significantly in the body of the tank-less water heater. Replaced the 10 year old rubber washer hoses with stainless braided and water hammer was back as if nothing had changed. Switch back to the rubber hoses and the hammer was still there. Put the new hoses back on and called it a night.
    The hammer noise is inside the tank-less water heater. All the shock waves seem to resonate there.
    I took some pictures of the plumbing layout and will try to post.
    Getting back to the tank-less WH where the noise ( bam, bam, bam ) is coming from. It is at least 12 years old Bosch AQ-125-HX- NG and has never been serviced. Inlet screen has never been cleaned. It still supplies plenty of hot water without any problem. Water supply comes from Lake Erie.
  19. boaterbill

    boaterbill New Member

    Messages:
    10
    Location:
    ne ohio
    IMG_0234 (480x640).jpg IMG_0235 (480x640).jpg IMG_0236 (480x640).jpg IMG_0237 (480x640).jpg

    There is a 1/2" line about 12" above the water meter to a tee going left then down. This 1/2" cold line supplies all the fixtures in the house except the tank-less WH. The tank-less supply line is the vertical 3/4 line out of the meter going up and to the right and loops back out of the tank-less for hot water supply.
    If you close the shut off cold water valve under the tank-less WH there is no water hammer sound when you turn off any cold water fixture.
    In the photo there is a piece of blue tape on the 1/2" supply. Can I replace this elbow with a vertical tee and place a hammer arrester on top there? Would that do and good and what type of an arrester and how large?
    The 3/4" line going vertical out of the meter has a white marker at the elbow going right to the tank-less, can I install something there that would be of any help?

    thanks boater bill
  20. boaterbill

    boaterbill New Member

    Messages:
    10
    Location:
    ne ohio
    My recent update:

    By using the shut-off valve (globe valve) before the meter as a throttling valve I was able to reduce the hammer shock to a 20 psi jump to 100 psi from the city 80 psi. Before it was jumping to 140 psi. Now there is only a faint thump coming from the tank-less WH. Is this an acceptable partial remedy? Will the 20 psi spike still cause damage?

    What I plan to do is replace the shut-off valve (wont completely shut off water flow) I 'm using to throttle the water, with a ball valve. Place a 1/2 globe valve to be used as a throttling valve on the 1/2" line to all cold water fixtures to duplicate current partial remedy. Then add small expansion tank on 3/4" line heading to the tank-less WH in hope of eliminating all the water hammer.

    All comments appreciated,
    boaterbill
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