OT- Where to position water hammer arrestor?
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  1. #1
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    Default OT- Where to position water hammer arrestor?

    I have a well (1.5HP pump), and about 50 feet away sits the 85 gallon water tank. They're connected with 1-1/4" pipe.

    I've noticed that when the pump shuts off, the PVC pipes that are near the tank jiggle a fair amount. So, I'm thinking of installing a water hammer arrestor to help minimize this effect.

    I've read a number of internet articles and they give some good information, and lots of useless information. But none of them address the question of where to position the arrestor relative to the rest of the system. Do I place it near the tank, or near the well head? My gut feel is near the tank, because that's where the pipes are moving. But I also wonder if the arrestor would be that effective there, since the tank itself sort of acts as a big arrestor itself....a big cushion of air and water.

    One thing's for sure...I can't place it midway between the tank and pump as those pipes are all buried.

    Anyone have any insights? Thanks.

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    My BIL just had a new house built and while I didn’t do an inspection, I noticed arresters places at the spigots for the washing machine.
    So my guess would be at the water tank.

    Edit

    I bought a house that was built in the 50s. When I gutted it, it had old school arrester. Basically a drip leg on hot and cold pointed up right before the bathroom faucet.

    Seems to be at point of use.

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    You might have a water logged tank with not enough air in it. Drain down the tank and charge it with air to half of your operating pressure. Alternately you have a check valve that closes too slowly. The water actually starts flowing backwards causing the check valve to slam with a bang. I had to find a very short stroke check valve, not flapper type, to cure this problem on a large pump. It used to slam so hard we were afraid of breaking pipes. Alternately you can get check valves that are very slow closing and that works too on really big pump systems.

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    I don't think a water arrestor will help on a well. The air in your pressure tank is in fact a giant arrestor itself. Did you check to insure you have 12 psi in the air bladder? It could be that the air bladder is defective and the air has leaked out.

    Like the old style pressure tanks that came with no bladder, a tank with a leaking bladder will still work, you just have to drain the tank a little and put in some air every few months as in direct contact, the air will slowly dissolve into the water.

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    Sioux Chief manufacturing has a pretty good paper on designing systems with water hammer arresters.

    Supply | Arresters & Trap Primers | Arresters

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    For your well pump I would put it right at the pump, a good sized one. Others mentioned to check the bladder tank, that is good advice, it IS a giant hammer arrestor. Pressure in bladder tank should be something like 4 psi above cut in pressure of pump, not 12 psi someone above mentioned.
    In my house I have a small hammer arrestor under the sink for the dish washer and two on each hose to the washing machine, two on the back of the machine and two more on the wall faucets. I still have to add them to the top of the hot water heater. A common reason that water heaters fail is water hammer, that is partly why new code is to have hammer arrestor installed on new houses.

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    Add the unit at the well head. Flow velocity is too high, replace with a lower flow rate pump. The pump you have is pumping probably 18 or more gallons per minute. A lower flow rate pump will pump the flow slower, but run longer than your current set up. Be sure you need a pump with that that flow rate into the storage tank. If you can lower the cut off setting, you will get a reduction in the movement, but not eliminate the movement. Plastic pipe expands in length and diameter under pressure. If your storage tank is located lower in elevation than the well head, add a arrestor at the highest point that you can access.

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    Quote Originally Posted by Booze Daily View Post
    My BIL just had a new house built and while I didn’t do an inspection, I noticed arresters places at the spigots for the washing machine.
    So my guess would be at the water tank.

    Edit

    I bought a house that was built in the 50s. When I gutted it, it had old school arrester. Basically a drip leg on hot and cold pointed up right before the bathroom faucet.

    Seems to be at point of use.
    I had new plumbing put in a few years back and they are at the spigots/faucets as booze said. Never heard a peep out of the pipes yet.

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    Not quite sure what's happening here.

    Is there a "bladder tank" in the circuit? 84 gallons is a standard storage tank size, have never heard of one with a bladder, though there might be ...

    And water hammer arrestors are commonly used at washing machines. Their valves close quickly, so even if there were a bladder tank in the circuit, water hammer can happen at the washer without them.

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    I'd play safe and fit one on the pump end and another the PV end, I mean it's only a tee, a verticle / rising length of tube ** and a cap

    ** the longer and bigger bore the better.
    Last edited by Limy Sami; 06-09-2021 at 07:39 AM. Reason: tix fyop

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    Thanks all. The tank is a new X-Trol 255 (81 gallon) with a bladder and I set it per the paperwork they sent....it is within a few pounds of the low pressure, something like 35PSI. i just checked it a month ago so I know it's 'good'. Actually, the last time I watched it come up was the day I checked the air pressure so I know the hammer happens with proper air pressure.

    The check valve...there are two. One down in the hole on the pump and one at the top of the wellhead. The one on top is a brass poppet type. I don't know how fast it operates but I do know it seals tight as I also checked it about a month back. I have a new valve (a US-made, SS poppet type) I plan to install soon so maybe I'll do that first to see if it helps.




    WX-255 Well-X-Trol Well Tank (81 Gal)

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    I vaguely remember that you want the arrester near the end of the direction the water is going, to buffer the momentum of all that water mass moving. If you are getting hammering when the pump stops, I would think it's from backflow to the check, and you want it by the pump?

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    Quote Originally Posted by GregSY View Post

    The check valve...there are two. One down in the hole on the pump and one at the top of the wellhead. The one on top is a brass poppet type. I don't know how fast it operates but I do know it seals tight as I also checked it about a month back. I have a new valve (a US-made, SS poppet type) I plan to install soon so maybe I'll do that first to see if it helps.
    Water hammer is caused by a valve closing abruptly. The whole volume of water in the pipe is rushing toward the outlet and suddenly there is no place for it to go, which causes a shock wave that bounces off the valve and back down the pipe. The arrester introduces a small compressible chamber which absorbs the energy of the shock wave. That's why they are always at the valve end of the run. A bladder tank, or even the old time storage tank, so long as it's partially filled with air will certainly function as an arrester, but is in the wrong place, near the well rather than the far end where the shock wave originates.

    The well pump shutting off should not cause water hammer, but those check valves can. When the pump shuts off there is still flow, but the pressure quickly decreases, causing the check valve to snap shut in the face of the still moving volume of water, causing the shock wave that moves the pluming. With the check valve now closed the bladder tank is on the far side of the valve and out of the circuit.The solution is to add an arrester chamber on the well side of the check valve, and close to it.

    The down hole check valve is likely so close to the pump that it's not causing water hammer.

    Dennis

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    I should be more clear; the topside brass check valve is on top of the well head. The tank is about 50' away and has no check valve near it. So you are saying the arrestor should be on the well side of the check valve and not the tank side? It seem that if it were, it would be isolated from the tank side and have no effect on the water column where I am seeing the hammer.

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    Quote Originally Posted by GregSY View Post
    I should be more clear; the topside brass check valve is on top of the well head. The tank is about 50' away and has no check valve near it. So you are saying the arrestor should be on the well side of the check valve and not the tank side? It seem that if it were, it would be isolated from the tank side and have no effect on the water column where I am seeing the hammer.
    I think people are having problems to visualize your system. I would suggest posting a dimensioned sketch of your system, annotated with where the banging is heard.

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    I've always put them close to the tank. This should remedy the rattling at the tank and will kill any rattling inside the house.

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    Quote Originally Posted by Superbowl View Post
    I don't think a water arrestor will help on a well. The air in your pressure tank is in fact a giant arrestor itself. Did you check to insure you have 12 psi in the air bladder? It could be that the air bladder is defective and the air has leaked out.

    Like the old style pressure tanks that came with no bladder, a tank with a leaking bladder will still work, you just have to drain the tank a little and put in some air every few months as in direct contact, the air will slowly dissolve into the water.
    12 psi? I'm pretty sure that my tanks all came with 28 psi and that's what I've always used on them. Shallow well pumps and a deep well jet pump.

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    Try it with the top check valve removed. Two check valves may be your problem.

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    Is this a new house, or a new plumbing job?

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    Just before a valve, the hammer is generally the shock wave travelling along from the valve back so the chamber allows the sudden fressure fluctuation to get dumped in compressing the chambers air space.
    Mark


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