Water hammer issue

Discussion in 'Irrigation' started by mitchgo, May 6, 2011.

  1. mitchgo

    mitchgo LawnSite Silver Member
    Messages: 2,956

    Honestly I'm looking for kirils thought on this, but decided to post so everyone can read and post if they like.

    Now I think we all know the cause of water hammer is a hard thing to diagnose because there are several different ( in no relation ) situations that can cause hammering. From high water pressure, loose strapped pipes, high fps, bad prvs to wrong pipe sizes and design, flow control, just a bad valve ect ect)

    I initially came to a house to do a sprinkler start up, the tech notes from last winterizing said she wanted us to look into some water hammering in the spring.

    Generally I'm only scheduled a hour for a tune-up , depend on the size of the system . So I was only scheduled for a hour, because our office lady sucks at giving us a good amount of time..

    I checked the system out and walked around with the homeowner and told her, at the end of the tune up I would investigate the water hammer issue.

    The lady said she has some water hammer inside the house from a particular zone ( Zone 6) which was the front yard lawn and shrubs.

    So after my tune up I walk inside the house and start turning on zones with my remote. Sure enough at zone 6 when it's turned ON you hear a huge amount of rushing water then a BANG BANG BANG BANG through out the entire house, the loudest water hammering I've ever freaking heard.

    So I go into her crawl space , crawled around and isolated the hammering within a 3' section of copper in the middle of the house. The piping is strapped and does not move with my hand nor when the hammering occurs from turning off/on the remote. The interesting thing after I turned off the zone I could hear water rushing for about 30 seconds as if it's filling up the house piping

    I didn't have as much time as I wanted to figure things out more but I'm looking for some possible answers

    The water meter is 5/8th's " at 72 static psi. The back flow assembly is tied off the service water line to the house 10' infront of the water meter, the plumbing at the back flow assembly is 1"- I don't know the size of the POC from the service line.

    The inside main copper pipe from where the water hammering is occurring is 1.5" and appears to be through the entire crawlspace as much as I crawled around.

    Zone 6- waters the entire front lawn and shrub, The back flow assembly is on the other side of the driveway. I didn't look for the zone 6 valve in the time I had allotted but it's safe to say that the piping does not go under the driveway for this zone and it goes around the house.

    Zone 6- Has about 13-16 spray heads ( 1800 series, about 1/2 non check, 1/4 sam's and also a few risers, some are VANS and most are fixed) My GPM check was just about at 16 GPM. I'm not sure of where the valve is, but fairly positive given the design of the system and that zone 6 takes about 45 seconds to fully pressurize that the valve is somewhere in the back yard. Total pipe to go around the house to the front yard from the back flow assembly is about 200'

    So this is my idea of what I think is happening and I want to be corrected if I'm wrong.

    The hammering only occurs when the valve is turned on and not when shut off. I first suggested because it's a particular zone, lets rule out the valve by replacing it.

    My idea is that when the valve is first turned on- a sudden rush of water flows through the open pipe. Probably easily pushing 25GPM +++, The 5/8th's water meter at 70 PSI ( factoring 200 ' psi loss, fitting loss and head loss) probably can't support this amount of flow. Well the piping inside is 1.5", that's a ton of volume of water for a house. So I think that water from inside is being sucked backwards to support the demand, thus causing back flow , creating a void of water inside the pipe and thus causing the back flow. My only belief on this is true is because you can hear water filling the pipes back up for at least 45 seconds after the zone shuts off.

    My solution to the woman was to replace the valve and that I wanted to split the zone ( It should have been 2 zones in the first place!) But given all the hardscaping this would be pretty dang costly .

    So I suggested a MPR conversion to overall reduce the Flow of the zone and reduce the FPS first, if this doesn't work then split the zone. I'm guessing after facting all losses my dynamic pressure of the zone is around 30-40 psi from a static 70.

    I was also thinking, which I didn't suggest to her yet though. Was to install a check valve on the service line just after the POC Tee. This would prevent any kind of water being sucked backwards.

    Watchya think guys?

    Some things I wanted to do if I had all the time i needed to fully investigate-

    * Find the valve, if it had a flow control and I turned it down and turned on the zone and watering hammer stopped. This would just about fully support my theory,
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,755

    First step - close down the zone valve flow control, and slow the inrush. Do nothing else until you try this. Step two would be a new diaphragm assembly, since the diaphragm is a part of the oscillation you are experiencing. (and it is an oscillation, as opposed to the classical sense of water hammer happening at a just-closed zone valve)
  3. DanaMac

    DanaMac LawnSite Fanatic
    Messages: 13,226

    Try turning off half the spray heads to reduce the flow. See if that takes care of it. Quick easy diagnosing method.

    I have one house from yesterday, same thing. Last year they had lots of hammering. I went to check it yesterday, nothing this year. But it is 3/4" supply, WaterMaster valves, 3/4" poly laterals, zones at 16-20 GPM. They work ok, but I am changing to two zones to the Toro Precision nozzles to reduce the flow.
  4. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,755

    ....and check the blinker fluid
  5. mitchgo

    mitchgo LawnSite Silver Member
    Messages: 2,956

    Sometimes when I come into these situations that I don't deal with too often, I don't always remember a good step by step process when i'm on the field, only afterwards when I have time to think about it is when I think ' I should have done that!'
  6. mitchgo

    mitchgo LawnSite Silver Member
    Messages: 2,956

    I actually wanted to do that, and told her' I bet if I turn off half the heads the hammering will stop"

    But at that point I was 15 min late to my next scheduled appointment..

    Hopefully the lady is willing to spend the money to get it fixed correctly ( didn't sound like it though even though she had a at least 600k house.... Biatch!!!
  7. AI Inc

    AI Inc LawnSite Fanatic
    Messages: 27,061

    Change those spreayers out to sams so your zones not draining empty.
  8. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,335

    I think you are on the right track with your thinking. Trapped air in the lines + high initial inflow + sudden directional changes in flow = massive water hammer, or in this case more appropriately called a hydraulic transient. 1.5 inch is a big line for a house, especially given the up/down stream piping and meter size. The bigger pipe should in theory dissipate the hammer more quickly, which suggests there may be trapped air in it which will make the hammer worse. A pressure relief valve or an air/vacuum relief valve (or a combo like the ComboAir ) on the 1.5 inch line may solve the problem.

    You might be able to fix it with MPRotators, however since the hammer is occurring at the initial opening of the valve and not when it closes this might not work. Keeping the line from draining is also a possible solution, although simply putting checks on all your sprinklers probably won't cut it unless you are certain there are no other "leaks".

    I do agree the zone should be split if at all possible, if for no other reason than more efficient water management. The added benefit to splitting the zone is you will probably eliminate the hammering as well. I would also try my best to find the loose pipe, closely inspect all the joints, and secure it better with more clamps/straps and perhaps even a thrust block.

    Problem with testing is you may only have one shot per trip, unless the line is draining out fairly quickly. Does the hammer occur every time the zone starts up, even if it is started right after it has been shut down? If it does, is it hammering at the same intensity as an initial firing of the zone after it has been sitting for a day or more?

    @ boots .... water hammer is oscillatory by nature.
  9. mitchgo

    mitchgo LawnSite Silver Member
    Messages: 2,956

    Thank you for your input kiril.

    If i turned on /off zone 6 fairly quickly with the remote, you would hear a little bit of hammering but not too bad. If the zone was off for say a minute the intensity would be as loud as I turned it on the first time.

    Actually , on all of the zones you hear a ' soaring' rushing sound of water for 1 or 2 seconds inside the house but zone 6 is the worst by far and the only one that does the hammering.

    Maybe there is a leak somewhere in the zone that's not surfacing , though just by looking at all the heads 16 GPM looks about right. The zone only has I would 3' vertical difference.

    I was thinking that too about the mpr conversion- It would reduce the flow of the zone but I think the sudden inrush would still be there.

    I think If I go back there ( She was concerned about cost, but jeez lady you have to get this fixed right??)

    I'm going to replace the valve- Nozzle everything down and check the meter for any major leaking of the zone, Convert to MPR rotator , Upgrade about 3/4 of the heads to SAM's where needed and see how it does.

    I probably won't suggest these but if it was my house I would probably put in the check after the POC and a water hammer arrestor inside the house.

    Kiril ,

    I heard that those vacumm breaker deals inside the house are supposed to have air pockets inside them and sometimes they fill up with water. At one point, I was suggested to turn off the water and drain the house line and turn it back on to get air back into those deals .
  10. mitchgo

    mitchgo LawnSite Silver Member
    Messages: 2,956

    Now that I'm thinking about it I want to check the houses shut off valve and make sure it's fully on, and check the pressure inside the house. I know those prv's don't act so well when water is flowing backwards through them

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