Severe water hammer with irrigation system on flow start not stop

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Jarniscipus, Jun 21, 2017.

  1. Jarniscipus

    Jarniscipus Member

    Joined:
    Oct 16, 2016
    Location:
    Prior Lake, Minnesota
    I have a new problem after re-routing some pipes that is making me crazy that I cannot figure out. I have a 25 foot run of 1" copper pipe inside my house that starts from my after my well inline filter. The copper runs through the ceiling and walls to an outside vaccum pressure breaker where it transitions to an irrigation system. Irrigation system is all poly with 13 zones and 78 rotor heads.

    The well has a 5 gallon pressure tank on it. PSI is 70 PSI at the well intake. I know that may sounds like a lot, but it has been at 70 PSI for 20 years with no problems with anything. My longest irrigation line is 1200 feet so I keep the pressure high to help.

    I have extremely severe water hammer in my interior 1" copper pipe inside the house only when the irrigation starts up. I run all 13 zones and there is no hammer when irrigation stops, opens or closes any valves after the first zone. The hammer only happens when the first zone is turned on. I can replicate the hammer by opening and closing a 1" ball valve inside the house between the well and copper internal irrigation run. The hammer only occurs when I open the ball valve, not closing it.

    The hammer is severe enough to feel and hear it anywhere in my house, it sounds like a gunshot and I am very concerned about my new copper pipes breaking over time. It is outrageously bad, like a thunder clap. It wake up everyone in the house!!! Very bad for my copper!!!

    I did something replumbling my house that created the problem or there is a coincidence here, but I just can't understand what I did or how to fix it. Of course I did the replumb in the winter and then drywalled and was not able to test the sprinkler system for 6 months, so now the walls and ceiling are sealed up. To bad for me and I hate drywall work, so I would like to avoid getting in there again. I did take a chance here replumbing in the winter because I could not test the pipes, but I am confident in my abilities so I was not worried about leaks or anything like that.

    Here is what I did that caused the problem. I had an 8 foot section of pipe in the ceiling that had 3 90 elbow in it (going around HVAC)- that was the old system, no problem. I changed that part of the pipes, keeping 3 90's, but extended a piece of copper pipe by 8" in between 2 of the 90's and maybe rotated one of the 90's 45 degrees. For the life of my, I cannot figure out how adding 8" of pipe could create the worse hammer I have seen in my life. Maybe it is a co-incidence.

    I tend to think this problem is arising from a slug of water hitting my pipes like a battering ram at one of the 90's, perhaps there is air in the ceiling pipes that is let in from the vaccum breaker? Is that possible?

    Does anyone have any thoughts? I am happy to do anything to fix it, my problem is that I don't know what to do make that happen. I am at a total loss how this happened from my replumb job.

    I have thought of putting in a 1" arrestor, but will this help on valve opening? Also the valve that opens for the first irrigation valve located 200 feet away from the water hammer.

    Thanks!
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    If I had to guess, and this is not all that educated! I'd guess that once the irrigation system is off, the vacuum breaker is allowing parts of it to drain. The rush of the water into the empty line then has to slow when it fills the line up. A 1" line holds a lot of water, and being pushed with 70psi, will develop a lot of inertia.

    I know you can't see it now with the drywall up, but how did you anchor the pipes, and, after the changes, is a section now much closer to some solid object? The way it was routed previously, it may have moved, but it didn't hit anything...it appears to be doing that now. You may be able to isolate closer to where it is, and only tear out some drywall. Clamps may help keep the line from moving and hitting something.
     
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  4. valveman

    valveman Cary Austin Staff Member

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    Does the pump start at the same time as you here the hammer? Or is the pressure tank still draining down to the pump start pressure?
     
  5. LLigetfa

    LLigetfa DIYer, not in the trades

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    Valveman may be on to something. Is there a checkvalve before the tank?

    Turn off the pump breaker when the tank is full and see if you still get water hammer. Also do a drawdown test on the tank to see how much it actually holds in reserve.
     
  6. Jarniscipus

    Jarniscipus Member

    Joined:
    Oct 16, 2016
    Location:
    Prior Lake, Minnesota
    These are good questions. As to the strapping of the pipes nothing has changed, they are strapped the same way. I can hold the pipes and hammer still occurs.

    As for the tank it is a 2 gallon capacity tank with a manufacturer spec drawdown of 0.6 gallon at 40/60 PSI. I am on a Gould's constant pressure system, so my pump runs whenever the water runs more than about 0.6 gallon which is basically all normal uses. It turns on in a few seconds when the irrigation valve opens. I did turn the pump off and there is hammer, but less than when it is on, which makes sense to me. There is no checkvalve before the tank. There is nothing new here, the pump still turns on at the same time as it did before the hammer problem, whenever, the valve opens the pump starts before and after hammer issue.

    Also, I did this replumb to code and had it inspected and the AHJ of 20 years in the area said it was one of the cleanest and well thought out plumbing jobs she had seen, so I don't think my work is a hack, but I screwed it up somewhere, so clearly I am a hack!

    I don't know what hte rpes
     
  7. Jarniscipus

    Jarniscipus Member

    Joined:
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    Location:
    Prior Lake, Minnesota
    These are good questions. As to the strapping of the pipes nothing has changed, they are strapped the same way. I can hold the pipes and hammer still occurs.


    As for the tank it is a 2 gallon capacity tank with a manufacturer spec drawdown of 0.5 gallon at 50/70 PSI. I am on a Gould's constant pressure system, so my pump runs all the time. Pump off pressure is 70 PSI and turns on and hold stable at 65 PSI


    I tested the drawdown in reality and it is not 0.5 gallons, it is 0.25 gallons. But I don’t know what it should be on a constant pressure system. The speced drawdown of 0.5 gallon at 50/70 does not seem meaningful because the system only draws down from 70 to 65 PSI. In fact I can’t find anything useful in Amtrol’s literature for a constant pressure system, it is all specs for conventional as far as I can tell.

    Air pressure in the tank is 40PSI. I have had some previous advise that on my constant pressure system well tank pressure should be about 20 PSI below cutoff pressure, which would be 45 PSI.

    Pump turns on in a few seconds when the irrigation valve opens. I did turn the pump off and there is hammer, but less than when it is on, which makes sense to me. There is no checkvalve before the tank. There is nothing new here, the well setup system is the same before the hammer. Nothing has changed. There are no checkvalves anywhere that I am aware of, there never has been any, other than the check valve/ball/flap or whatever it is on the well pump that is 375 feet undergound. The checkvalve on the well pump is good in my opinion, not that I am a well driller, because the well does not leak down quickly.

    Also, I did this replumb to code and had it inspected and the AHJ of 20 years in the area said it was one of the cleanest and well thought out plumbing jobs she had seen, so I don't think my work is a hack, but just because it was inspected does not mean it is correct as we all have experienced I am sure.
     
    Last edited: Jun 22, 2017
  8. valveman

    valveman Cary Austin Staff Member

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    Amtrols WellX1 and Goulds Aquaflow/boost are two completely different animals. I am guessing you have the Goulds as it works with 5 PSI differential where the Amtrol usually works with 10 PSI differential, and the Amtrol doesn't run the pump all the time like with the Goulds system. Neither one of these systems have been around for 20 years, so you must have had something different previously when you say it has always been at 70 PSI?

    I also do not understand how you could still have water hammer, or water at all when the pump is off? And with 5 PSI differential you are lucky to get .6 gallon draw from a 5 gallon tank. You need the full 50/70 bandwidth to get 2 gallons of draw down from that tank.

    Have you checked the tank to make sure the diaphragm is not bad? That is really the only thing still active when you turn the pump off, but it is only active for a second or two.
     
  9. Jarniscipus

    Jarniscipus Member

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    Location:
    Prior Lake, Minnesota
    Sorry for the confusion on my post, I tried to edit my post and ended up with two weird double posts. You are right valveman, I have the Goulds system, the Amtrol I refered to is the the 2 gallon pressure tank.

    I probably did have something different 20 years ago and did not pay attention to what changed or I forgot - the well driller has made some changes over the years as things break. I know I have had this system long before the hammer started, however many years that is.

    The tank appears good. It is not water logged and holds 40 PSI air pressure, from what I can tell. Draw down tested by me is 0.25 gallons on the 2 gallon pressure tank before the pressure drops to 65PSI and the well pump kicks on. It takes a few seconds.

    I still do get hammer when the pump is off when I tried turning the pump off becauase when I turned off the pump, the system still holds 70 PSI for a long time. So I still had a momentary pressure for the hammer to occur, but it was a lot less than with the pump on. Of course I only get water flow for a few seconds from the residual pressure in the tank and pipes.

    I did run my irrigation last night and was able to stop the hammer by first closing the main water valve at the well system and then turning on the irrigation (first zone valve open with no flow) and then if I slowly open the main water valve, the hammer does not happen, so obviously it has to do with a high degree of flow/pressure at once.

    I can replicate the hammer by opening and closing the main water valve with the irrigation valve also open. Hammer only occurs when I open the valve and not close it. With the irrigation valve closed, no hammer occurs. This makes sense to me because if the irrigation valve is open 200 feet away and the sprinkler heads are open, there is no pressure on the system and every time I open the main water supply valve, there is a huge pressure differential. If I open the valve slowly, then there is no hammer at all.
     
  10. valveman

    valveman Cary Austin Staff Member

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    Can you show us a short video of the pressure gauge when this happens? If it is happening around 40 PSI, I am guessing the small draw down from the tank, coupled with the slow start of the variable speed pump system is causing the bladder in the tank to bounce like a basketball on a hardwood floor.
     
  11. LLigetfa

    LLigetfa DIYer, not in the trades

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    Often there can be a discrepancy between the two gauges (water and air) when checking the air precharge. If you don't have the right precharge, then as valveman says, the bladder can slap the bottom of the tank.
     
  12. Reach4

    Reach4 Well-Known Member

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    45 PSI will be better than 40 for the life of the pressure tank. I don't think that would cure your symptom, however.
     
  13. Jarniscipus

    Jarniscipus Member

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    Location:
    Prior Lake, Minnesota
    You guys are awesome for the help and I think you are on to the problem. So I did take a video and posted the link below. The gauge filming when the valve opens is at 55 seconds and there is a massive drop in pressure from 75 to 30 PSI. Normal pressure drop with faucets, toilet, shower, etc. on the 1/2 and 3/4 branches is 5 PSI to 65PSI. I think the 1" irrigation pipe really drops the pressure big time.

    Here is the thing, there is severe hammer all the time, except for when I filmed it....it now is not happening!!!! I can't believe it, my water hammer is camera shy! I dont' even know what to say about that. I am going to try and film it again later today to see if it happens again. it is like people taking their car to the mechanic and the problem is gone!

    I did do one thing since the hammer occurred. I turned the pump off and drained the water from the tank to test the pressure on the tank, which was about 40PSI. I don't know how this could have changed anything, but perhaps I had air trapped in my pressure tank below the bladder that is now relieved??? Is that possible? However, you can hear it a little bit around the 30 PSI drop, but it is minor and not major.

    So what is the consensus on the tank pressure? Water pressure is 70 PSI, tank pressure is 40 PSI (actually I rounded, it is 38 PSI). Should I put more air in the tank and how much? Thanks reach for suggesting 45 PSI, I can do that, does anyone think I should go higher?

    Here is the video where my complete plumbing system can be seen with the water hammer that is camera shy at 55 seconds. I will note there is some hammer on valve closing, but it's minor and does not happen when the irrigation valve closes 200 feet away

     
  14. Reach4

    Reach4 Well-Known Member

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    Those jumps are odd.
    At about 0:57 there is a big drop below 50 before the spike down about 0:58. Then about 1:00 to about 1:15 the pressure is around 48. So even disregarding the spike down, this seems more like a 48/70 system than a 65/70 system.

    It is like the pump cannot keep up with that zone's water needs.
     
  15. Jarniscipus

    Jarniscipus Member

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    Prior Lake, Minnesota
    It is a 65/70 system 99% of the time on all normal water use, except when the irrigation starts on zone 1. If you watch it to 1:31 the pressure goes back up to about 66 and stays there with the sprinklers on, so it does run at 66 PSI on that zone.

    My irrigation line on #1 zone on pump startup is a 1000 feet long on a grade downhill, so when the sprinklers stop the 1000 feet of line drain out throug the lower sprinkler heads and the pump has to fill and repressurize 1000' of pipe. I suspect that is what the lag is and the pressure drop, is that 1000 feet. Once zone 1 is done, the 1000 feet of pipe are filled with water and the next zones do not have as much of a fill time.

    I don't think pump sizing or irrigation system is the issue because there was no water hammer for many years until recently and it's all the same system....I didn't change anything well or irrigation system. This is why this is so weird to me.

    And now even weirder that it did not do it while I was filming when the only thing I did was drain the tank to check the air pressure.
     
  16. Reach4

    Reach4 Well-Known Member

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    How many GPM does your pump make? I wonder how a Dole valve on the zone 1 line, that limited the flow to that many GPM, would do.

    I don't know irrigation or pump systems like yours.
     
  17. Jarniscipus

    Jarniscipus Member

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    If I am not mistaken, which I probably am from memory recall, I think it puts out approximately 25 GPM at the surface after consideration of a 350 foot head, it is for sure somewhere in the range of 24-27 GPM, at least that is what I was told. It really rips putting water out a 3/4" hose in the yard
     
  18. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    So, your cutoff pressure on the pump is 70#...what is the turn on pressure set to in the pressure switch?

    The bladder tank's precharge pressure should be 1-2# below the turn-on pressure If I remember correctly. NOte, that you can only check that when it's not full of water, a valve is open, and the pump is off. If the bladder tank's pressure is above the turn-on pressure, you can run out of water before the pump turns on. If it's below the turn-on pressure, there should always be at least a little water left in the tank before the pump turns on.
     
  19. Reach4

    Reach4 Well-Known Member

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    His cut-on is 65, and cut-on is 70.

    I am going to amend my precharge suggestion to 48 PSI to help the tank life. That is not going to help the bang problem.
     
  20. Jarniscipus

    Jarniscipus Member

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    Thanks Reach, I will set it at 48 and try a Dole valve once I get the specs. I will also post back this week sometime or next if the bang comes back, I am sure it will. Can I put a Dole valve outside after the vaccum breaker? That would be very easy to do, rather than fiddling around inside the house - do Dole valves do ok with freezing after water is blown out of the line and will they stand up to being blown out with compressed air (I do that in the fall).
     
  21. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    If your pump turn-on pressure is really 65psi...your precharge in the tank should be in the order of 63psi, not 48. Find the manufacturer's instructions and follow them. When it's that much less, it will stretch the bladder much further than it's supposed to, shortening it's life. Having that small of a differential will cause the pump to cycle lots more than optimal, shortening its life, too. A cycle stop valve might work out for you to maintain pressure.

    A more typical pump pressure switch has a 20psi differential, not 5, and thus, 70-20 = 50, so 48psi should work, too. IMHO, a 5psi differential is not a good thing with a conventional pump control.
     
    Last edited: Jun 25, 2017
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