water hammer on supply side of pressure tank

[law2lake]

The well is drilled, approximately 120 feet deep. It was drilled in 2006 when I constructed my home. In the basement of the house, the main water line comes in and connects to Gould V60 pressure tank. The pressure switch is 30/50 and the bladder is pressurized at about 27. There appears to be a check valve in the T package on the supply side of the T. I have not noticed any loss of pressure in the tank.

My well water system works perfectly, EXCEPT when it has been sitting for a period of time (hour or more). On the supply side of the pressure tank, when the well first turns on in the morning (after toilet is flushed, water running, etc.), there is a single pound hammer that can be very loud at times. Once this happens, as long as we use water on the regular basis, we will not hear the noise again. However, if it sits for a while (hour or more), the same bang.

My theory is that the foot/check valve located at the top of the submersible pump (or wherever it is located), has gone bad, allowing the water in the line from the pump to the pressure tank to leak out, replacing it with air, and causing a hammer-type bang when the pump turns back on.

Unless we use water in the house, the pump does not cycle on/off. I assume that is because the check valve on the t-package is preventing any water in the pressure tank from leaking out.

Any thoughts on other things I can check before calling my well guy to pull the pump and replace the foot/check valve?

Thanks for any guidance.

 

[LLigetfa]

Take out the checkvalve at the tank and the checkvalve at the pump will then hold with the aid of pressure against it.

 

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[Reach4]

It would be best to have the top checkvalve removed if your jurisdiction permits the well person or plumber to do that. If you DIY, the effect of a misguided code could be ignored.. If you do that, and if if your bottom check valve has a slight leak, then your pump may quietly turn on every few hours to compensate. I don't know what the period would be for that bottom checkvalve to leak 5 or 6 gallons. Maybe that bottom valve will behave better once it has more pressure against it.

You have a 20 gallon pressure tank with a claimed draw down of 6.1 gallons. That is probably smaller than optimum. Your pump should run at least a minute each time.

I am not a pro.

 

[hj]

quote; allowing the water in the line from the pump to the pressure tank to leak out, replacing it with air

Your theory is correct, EXCEPT, air does not suddenly appear from nowhere. The pipe has to have a small leak so it can "suck" air in as the water drains down. The smaller the leak the longer the process will take.

 

[LLigetfa]

I doubt that air is getting sucked in. If it was, you would get spitting at the taps and it would probably be heard entering the tank. Air in the line would act as a cushion, softening the impact.

Depending on how far down to the water level in the well, the water column may fall creating a partial vacuum. When the pump starts, the column of water rushes in and slams the check at the tank.

 

[law2lake]

It would be best to have the top checkvalve removed if your jurisdiction permits the well person or plumber to do that. If you DIY, the effect of a misguided code could be ignored.. If you do that, and if if your bottom check valve has a slight leak, then your pump may quietly turn on every few hours to compensate. I don't know what the period would be for that bottom checkvalve to leak 5 or 6 gallons. Maybe that bottom valve will behave better once it has more pressure against it.

You have a 20 gallon pressure tank with a claimed draw down of 6.1 gallons. That is probably smaller than optimum. Your pump should run at least a minute each time.

I am not a pro.

I like your idea. If I remove the top checkvalve, and there is still a problem, I think I have narrowed the problem to somewhere before the tank.

As for the size of the tank, any suggestions. My wife and I live in this one family home alone.

Thank you.

 

[law2lake]

I doubt that air is getting sucked in. If it was, you would get spitting at the taps and it would probably be heard entering the tank. Air in the line would act as a cushion, softening the impact.

Depending on how far down to the water level in the well, the water column may fall creating a partial vacuum. When the pump starts, the column of water rushes in and slams the check at the tank.

Good point. No spitting at any time. As for the water column, I do not think it is dropping, but is there a way to check? Thanks.

 

[Reach4]

As for the size of the tank, any suggestions. My wife and I live in this one family home alone.

What I would suggest is to have one person with a watch/timer to sit by the pressure switch and gauge. Another person runs water until the pump turns on, and then immediately closes the faucet. Time how long the pump runs. It should run 60 seconds or more if the tank is properly sized. If it ran 40 seconds, I would not feel good about it. However I would probably not replace or supplement it immediately, but I would plan to upsize the next time there was a tank failure.

While thinking about it, do you have a control box with a capacitor in it? If so, those have a limited life. Few people do it, but it seems to me that to test and/or replace that capacitor after several (8 ... 10?) years would make sense. They are non-polarized electrolytic capacitors. Preventive maintenance like this is not often discussed. Those capacitors are only used during starting. A "2-wire pump" (which may have a third green ground wire) does not have such a capacitor.

 

[LLigetfa]

The water column could drop like mercury does in a barometer.

To mitigate the small tank and short cycles, consider a CSV.
http://cyclestopvalves.com/index2.html

 

[law2lake]

Can someone confirm that the copper colored piece on the supply side of the T (closest to PVC) is a check valve. This is what I am assuming is the check valve that apparently should be removed.

Thank you.

 

[LLigetfa]

Yes, except it is brass, not copper.

 

[law2lake]

FYI, based upon your information and information that I received from other forums, I replaced the check valve just before the tank, and the hammer is gone! And it is holding pressure just fine. Apparently, there is no need to have more than one check/foot valve in my system. Sometime less is more. Quiet as a mouse. Thanks for your assistance.

PS. It is amazing how many people told me that multiple check valves are not the problem. However, my gut told me that you all were right.