Could this cause water hammer in domestic cold water?

invermont

Plumbers came Friday and installed this new tank when I was at work. I’m going to call them Monday. Just want some advice before I talk to them. Never had hammer before, now I’m getting it in my cold water at all taps. Just one bang. If I remember right unsupported pipes can cause this? Or is it the way the new tank was installed? The hot and cold run behind a manifold wall before the individual valves. Looking behind the wall I see ten + or - feet of unsupported pipe from work done ten years ago. The valves branch

from an original pipe that feeds the older part of the house.

the_donut

Usually happens when water flow stops or change direction suddenly with pressure. I would check pressure on compression tank. Should be around 60 psi.

You may have had larger diameter pipes in a branch and tee setup before. The velocity was lower in these pipes. You can try reducing the tank pressure or installing water hammer arrestors.

hot_rod

What is your incoming water pressure/ 45- 60 psi iOS plenty. the higher the pressure the more prone to hammer when valves close quickly as donut mentioned.

Water hammer arrestors are best at the place the hammer is created, wash machines, dishwashers, etc. anywhere a fast close valve is. the thermal expansion tank should help control hammer potential also. check incoming pressure and pre-charge in the tank.

Larry Weingarten

Hello, Did they install a swing check valve anywhere? That can be a source of noise. By the way, that T&P in the end of the "T" is not sensing actual tank temp as well as it could, unless they used a special T&P that has an extended probe.

Yours, Larry

Pumpguy

I've had this problem before and here's what I did to cure this water hammer problem:

1) Turn off the main valve where water comes into the house.
2) Go around the house and open all the faucets until no water comes out. This should include clothes and dishwashers; anyplace where you had water hammer. They should all be left open until no more water comes out.
3) Close all the faucets.
4) Open the main water valve to the house.

What this does is drains all the water from the system including the shock arrestors. When you refill the system, air is now trapped in the shock arrestors, providing the needed air cushion to prevent the water hammer.

Hope this works for you.

invermont

Larry Weingarten said:

Hello, Did they install a swing check valve anywhere? That can be a source of noise. By the way, that T&P in the end of the "T" is not sensing actual tank temp as well as it could, unless they used a special T&P that has an extended probe.

Yours, Larry

Larry, if you look close there is a swing check valve right before the expansion tank. It hidden behind other pipe. I held my hand on the pipe about a foot in front of it this morning and I can feel the vibration really well there. Is that normal? Will it hurt anything?

Leonard

Unsupported pipes aren't going to cause a water hammer, but they may rattle around when one happens and make additional noise.

Water hammer suppressors are just effectively a capped off vertical section of pipe that holds air to act a spring to cushion fast flowing water to a stop.

My Guess is when they installed the new water heater they removed some piping that acted a water hammer suppressor.

Larry Weingarten

Hi, If you feel like testing my check valve theory, remove the disc from inside of the check, reassemble the valve and see if the hammer is gone. If you must have a check valve there, use a spring check with a soft seat, so it doesn't chatter. What you describe with one bang at all taps is something I've met before, and always caused by a swing check. Do you know what the static water pressure is?

Yours, Larry

MikeL_2

I've found that home made shock absorbers or air chambers become water logged rather quickly. I prefer to install manufactured water hammer arrestors; in some cases of water hammer, a strategically located thermal expansion tank will serve the same purpose.....

invermont

Larry Weingarten said:

Hi, If you feel like testing my check valve theory, remove the disc from inside of the check, reassemble the valve and see if the hammer is gone. If you must have a check valve there, use a spring check with a soft seat, so it doesn't chatter. What you describe with one bang at all taps is something I've met before, and always caused by a swing check. Do you know what the static water pressure is?



Yours, Larry

I’m not sure what the static pressure is. My old tank didn’t have an expansion tank or check valve. The hammer is right before the check valve. I never had the hammer before, only a quick release of pressure when I opened a hot water spigot. Can I play with the pressure in the expansion tank to control it?

invermont

Leonard said:

Unsupported pipes aren't going to cause a water hammer, but they may rattle around when one happens and make additional noise.

Water hammer suppressors are just effectively a capped off vertical section of pipe that holds air to act a spring to cushion fast flowing water to a stop.

My Guess is when they installed the new water heater they removed some piping that acted a water hammer suppressor.

There wasn’t much to the old tank. Just a diverter.
Here is a photo, if you zoom in on the tank you can see the setup

Larry Weingarten

Hi, Static pressure matters for at least two reasons. First, without knowing that number, you can't know what to charge the expansion tank to. There have been discussions here about charging the tank, with some saying charge it a bit higher than static, but within five psi of static should be OK. I aim for the charge matching line pressure. Second, if the pressure is high, it makes water hammer worse. I like to see pressure in the 40-60 psi range. You might have a pressure reducer on the incoming line, but they don't last all that long. In my area they last around five years. It could be that when pressure is under control, the water hammer problem will go away.

Yours, Larry

ps, The expansion tank needs to be charged when isolated or removed from the system.

invermont

Larry Weingarten said:

Hi, Static pressure matters for at least two reasons. First, without knowing that number, you can't know what to charge the expansion tank to. There have been discussions here about charging the tank, with some saying charge it a bit higher than static, but within five psi of static should be OK. I aim for the charge matching line pressure. Second, if the pressure is high, it makes water hammer worse. I like to see pressure in the 40-60 psi range. You might have a pressure reducer on the incoming line, but they don't last all that long. In my area they last around five years. It could be that when pressure is under control, the water hammer problem will go away.

Yours, Larry

ps, The expansion tank needs to be charged when isolated or removed from the system.

I will have to get a guage. I’m out of town at the moment, but I can stop somewhere tomorrow and get one

kcopp

Pretty sure its that silly swing check.
It does not need to be there.

invermont

kcopp said:

Pretty sure its that silly swing check.
It does not need to be there.

Was thinking the same

hot_rod

if it is a public water system there is possibly a back flow device somewhere?

A swing check is not really a good check to use, if a check is needed at all for some reason?

A swing check needs a pressure differential to seal well, and since they have a long stroke distance they will really bang. They also need high flow rates to swing open fully or they can chatter, they are very high Cv valves. They are best used for sump pumps

You'll notice BFDs have soft, cone shaped, spring checks for noise free operation.

HomerJSmith

A condensing of thought.

A spring check is best in this application.

The domestic cold water should be at 45 to 55 psi, use a hose bibb gauge to check. If too much higher, install a pressure regulator.

The X-tank air charge should be set at the same pressure as the domestic cold water.

The T & P valve must have a 8" probe and not the standard 4" probe. The probe must extend into the tank.

Your water hammer occurs when you shut the faucet off, not on, correct? I'm trusting you as to the sound being water hammer, is it? Put your hand on the cold angle stop under the sink and have someone turn the cold water on, run, and then off. You should feel a vibration and the sound should be localized.

If you shut the cold water off slowly, do you get the sound? What is the sound at the HTP tank when you shut the cold water off, normally, at the faucet?

Linear momentum of the flow of water being suddenly stopped creates the hammer. Usually fast acting solenoid valves on washing machines are the culprit.

You say that you feel the greatest vibration at the check valve. This leads me to suspect that it is the check valve slamming shut because of pressure differences between the cold water supply and the hot water circuit.

If the X-tank has too high an air charge over domestic cold water pressure, when the HTP heat up to 145 or higher degrees the expanded water will be forced into the X-tank at higher pressure.

To reiterate, if the X-tank is air charged to 80 psi, the HTP tank, as the water expands, meets that pressure in the x-tank as the water has to go somewhere. The x-tank, HTP tank, and piping has a system pressure of 80 psi or higher. The cold water circuit is at a lower pressure, 55 psi? When you open a faucet that is a blended mix, both hot and cold, the pressures would try to equalize, possibly opening the flapper on the check valve and slamming it shut again. Just a thought.

I would make sure that the X-tank air charge and the domestic cold water pressures are the same and replace the swing check valve with a spring check valve. Do that and report back.