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Water hammer damage (photos, please)

Discussion in 'Irrigation' started by Wet_Boots, Oct 24, 2010.

  1. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,334

    Is this the same problem as before with the 80 PSI supply?

    My best guess is pressure pulsation caused by the system startup & poorly secured piping. You might be able to fix it by regulating the pressure to the house.

    Messages: 18,668

    Well boy genius the zone split has nothing to do with water hammers. If you have 10 heads is it better to split to 5 on each side or just run 10 heads from the valve in one long run? I know how i'd do it and i would incorporate good strategies to avoid water hammers as well. Take your complete and udder bs straight to the source and be sure and cc jess.
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  3. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,334

    Then why did you mention it in a thread about water hammer, and a post about water hammer? Is this another one of those communication mishaps?

    Already said how I do it .... lateral main done the center (turf zones), sprinkler laterals off of that. This gives you the best distribution of pressure and flow for the zone ... you know ... before the days of pressure regulating stems.
  4. 1idejim

    1idejim LawnSite Fanatic
    Messages: 11,160

    taken from jess strykers irrigation tutorial

    Solutions for Water Hammer Caused by Irrigation Systems:

    The easiest solution is to lower the water pressure for your entire irrigation system. This doesn't really get rid of all of the water hammer, but it will sometimes reduce it to a level you can live with. Of course often when you lower the pressure enough to stop the water hammer the sprinkler system stops working too. Lowering the pressure has two effects. It lowers the water demand of the sprinklers, which in turn reduces the velocity in the pipes. That actually reduces the water hammer. Lowering the pressure also reduces the overall surge pressure when the water hammer occurs. That simply reduces the severity of the water hammer, but doesn't get rid of it. To test if this will eliminate the noise, simply go to the main shutoff valve for the sprinkler system. (If your sprinkler system doesn't have a shut-off you will need to install one.) Close it down until it is about 50% closed. Now run the sprinkler system. If the water hammer is still there, close the valve a little more and repeat. Continue this until the water hammer goes away. When the water hammer is gone, check your sprinklers. Are they still operating correctly? If they are operating correctly the water from any single sprinkler should be spraying almost all the way to the adjacent sprinkler head (you need about 80% overlap of the water between sprinklers to keep from getting dry spots.) So if the sprinklers are 18 feet apart the water from each one should be covering an area at least 14.4 feet out from the sprinkler (18 x 0.80 = 14.4). If the water is not going far enough you will get dry spots, so this solution will not work. If the sprinklers seem to be still working good leave the valve partially closed for a few days. Do any other problems shown up? Like the showers don't work in the house or dry spots show up in the lawn? If not you should go to the plumbing store and buy a good quality, brass bodied, adjustable pressure reducing valve. Install it right after the shut-off valve that you partially closed. Then open the shut-off valve fully and adjust the pressure reducing valve until the pressure is at a level where the sprinklers work right but the water hammer isn't a problem. You should not leave the shut-off valve partially closed for more than a couple of weeks. Most of those valves are not designed to be left permanently in a partially closed position. Also the pressure reducing valve is designed to compensate for changes in the incoming water pressure to your house. The shut-off valve can't do that. If only one valve zone of the sprinkler system creates water hammer you can try partially closing the flow control stem on the irrigation control valve. If that works, the flow control may be left in a partially closed position permanently, it will not harm the valve.

    If you have an automatic sprinkler system you may be able to get rid of the water hammer by simply changing the order in which the valves operate. Simply find out which valve uses the least water. This will probably be the one with the least sprinklers, but not always. Some sprinklers use more water than others. Once you know which valve uses the least water, rewire the controller so that the valve that uses the least water is the last valve to run. If you don't know which one uses the least water just try all of them in the last position. Since water hammer is directly related to flow, the valve that uses the least water is much less likely to cause water hammer when it closes. The reason putting this low flow valve last works is because most irrigation valves close slowly. So typically valve #4 will not have completely closed when the next valve, #5, opens. So when valve 4 snaps closed it creates a shock wave (water hammer), but the wave passes harmlessly out of the system through valve circuit #5. Don't worry if you didn't understand how that works, just try switching the valve order on the controller and see if it gets rid of the water hammer problem! (My thanks to Larry Welch for pointing this trick out to me!)

    The next step is to try a water hammer arrestor. As noted before, this often doesn't work with sprinkler related water hammer, but it's worth a try. At your local hardware or home store look for a pre-packaged water hammer arrestor that attaches to a standard washing machine cold water outlet. The ones I have seen come in one of those clear plastic display packages, and look like a copper tube with hose connections. Check the return policy of the store before you buy it, will they take it back if it doesn't work? Make sure you keep all the packaging. Install it per the directions on the package, try putting it on a hose bib close to the point where the irrigation system connects to the house water. If you have a hose bib on the irrigation system mainline, that is an even better place. Or you can tap into the irrigation mainline to install it. If it doesn't work, remove it and return it.

    If the noises were caused by an irrigation valve, then it is likely that someplace between the water source and that valve the water velocity is too high. Too much water is trying to squeeze itself through the pipe. To get through the pipe the water moves faster (higher velocity) and the faster it goes, the worse the water hammer gets. You have to reduce the speed of that water to get rid of the water hammer. Here are some ways to do that.

    The irrigation valve may be too small. This is seldom the problem, but I mention it because it is possible. If the valve is the same size as the pipe it is installed on (say, 1" pipe with a 1" valve) then it is extremely unlikely that the valve size is the problem. If the valve is one size smaller than the pipe (say, 1" pipe with a 3/4" valve) then there is a very small chance that the valve is the problem. It is normal to use a valve one size smaller than the pipe, so this is still is not very likely a problem. If the valve is a couple of sizes smaller than the pipe then there is a reasonable possibility that a larger valve will fix the problem. Also, cheaper valves often snap closed faster than more expensive ones. So a cheap undersized valve might be a good possibility as the water hammer source. It might be worth the effort of replacing the valve.

    This next option was once a good one, but now it seldom works because very few of these old sprinklers are still around. Really old sprinkler systems (15 years or more) used sprinklers heads that had a much higher water demand than today's sprinklers. Typically these sprinklers were made of solid brass. Thanks to engineering advances newer sprinklers have similar performance but use much less water. You could try replacing the old sprinklers with the new, low-flow sprinklers. Start by doing some research. Note the sprinkler manufacturer's name and the sprinkler model number of the existing sprinklers and do a search for that name and number on the Internet. If the sprinkler is no longer made that's a good sign. If you can find it check with the manufacturer to find out what the GPM of the sprinkler is. GPM is the gallons per minute of water the sprinkler uses. Next check how far apart the sprinklers are installed from each other. Take that number and multiply it by 0.80. So if the sprinklers are 18 feet apart you will get 18 x 0.80 =14.4 Round up, so use 15. The replacement sprinkler will need to have a radius equal to that number, so in this case it will need a 15 foot radius (not diameter). Go to the store and look for sprinklers that cover that radius. Then check the GPM demand of the new sprinklers. If they use less water than your current sprinklers you can replace the old sprinklers with new ones. It may get rid of the water hammer. It may not. But even if it doesn't work you get a better irrigation system. Note that if you are using pop-up sprinklers always use the ones with retraction springs. I recommend at least a 3" pop-up height to reduce maintenance problems.

    Splitting valve zones is another method of getting rid of water hammer. If only one of the irrigation valves is causing water hammer the easiest solution is to reduce the amount of water that valve is using. That will reduce the velocity and the water hammer will stop. To do that you need to reduce the number of sprinkler heads the valve operates. The easiest way to do that is usually to install a second valve and connect half the sprinklers to it. That's likely going to mean doing some trenching and installing some new pipe. So before you do that, you should run a simple test to make sure it will fix the problem. Remove half the sprinklers controlled by the valve and put a cap on the pipes where they were. Now turn on and off the valve several times to test for water hammer. If possible test the valve multiple times at different times of the day over a period of a week. If the water hammer only occurred at certain times of the day be sure to test at those times. For example, often water hammer problems are much worse at night, so it's a good idea to test a couple of times late at night. If the water hammer is gone, it worked! If the water hammer is still there you may need to remove even more sprinklers. If you remove all the sprinklers and the water hammer is still there, that valve is obviously not the problem! If the water hammer goes away when you reduce the number of sprinklers, then you will need to install a second valve and pipe to provide water to the sprinkler heads that were removed. Make sure the second valve has the same number or less sprinkler heads as the original one. You don't want to create another water hammer problem! You may even have to install 3 valve circuits where there was one originally.

    If the water hammer occurs when several valves close you can split each of them into two or more valves as described above. But you may find that it is easier to install a new, larger pipe to all of the valves. Remember, when water hammer occurs due to a closing valve it is because the water is going too fast in a pipe someplace on the upstream side of the valves. In order to understand this next procedure you need to be familiar with the relationship between your house plumbing and your sprinkler system and you need to know some terminology.

    Messages: 18,668

    This discussion is over for me.

    Nothing to do with your post jim. I read jess as well.
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  6. Mike Leary

    Mike Leary LawnSite Fanatic
    Messages: 23,103

    Good, we can get in our little chairs and get some serious design work done. crayola.com
    Last edited: Oct 24, 2010
  7. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,334

    Sorry Dad ..... I was busy making mommy a crayon dress.

  8. txirrigation

    txirrigation LawnSite Senior Member
    from Texas
    Messages: 977

    And I have thought this whole time irrigation was straight forward.

    Air hammers can be tricky, and each one is different. Altough the quotes provided from the books were good ones, the only real way to learn about air hammers is to have fittings blow apart on you 7-10 times in the real world.

    This is the learning process:

    1st blow out- PISSSED
    2nd - Refer to #1
    3rd- Frustrated
    4th-8th refer to #3
    9th- Fixed a lot of things that had NOTHING to do with the problem
    10th- Figured it out and moved on hoping no one ever finds out what happened on the job.
  9. Mike Leary

    Mike Leary LawnSite Fanatic
    Messages: 23,103

    Very nice sonny, keep your lava lamp away from mom's dress, now, or it's a night in the outhouse again.
  10. DanaMac

    DanaMac LawnSite Fanatic
    Messages: 13,187

    I do have one customer that called for a blow out, and said she "once again" needs us to look into the hammering and noise of the system when it runs. I told her, again that I cannot conclusively say what the issue is or how it can be fixed. I have told her multiple times it is due to how crappy the system is installed, both design wise and quality of components. It's not so much a hammering, but the rumbling due to high velocity from stretched zones. Nothing I can really do, short of redesigning the whole thing. They are Orbit valves so no flow control to throttle down which can sometimes reduce the noise, but it's just masking the problem.

    If I remember right, the zones are at about 18 gpm with a 3/4" copper supply line. Pressure has been increased to keep the zone working.

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