Cyclic Water Hammer in Copper Pipes: Solutions for Hot Water Tank & Expansion Vessel Capacity

Hello.
My problem is that when I turn the water around it takes about 2-3 seconds. You can hear the characteristic vibrations (knocking) of pipes heard throughout the house. It does not matter which tap I turn off, whether on the 1st or 2nd floor. The pipes always vibrate similarly to a water hammer. All batteries are sealed. It is an installation in a single-family house. The distance between the tank and the last tap - about 12m. Everything is made of copper fi 22, 18, 15, pressure behind the meter is about 4bar (reducer), hot water tank - 350l, heated by a central heating furnace.

Will the installation of an expansion vessel solve the problem? if so, what capacity. I am asking for your advice for which I thank you in advance.

Probably the classic operation of the proportional regulator. I am a bit unsure how you supply the house, but it comes out of the water supply. You have an airbag (definitely a tank) somewhere in the installation, which increases the so-called time constant of the regulator. The situation is probably aggravated by the high capacity of the connection and, of course, the reducer. I would try to remove this air, or at least minimize and choke the flow. I would expect to be at least one hit. Another thing, do you need such pressure in a single-family home?

Oki, thank you very much for the hint. I will try to do as you advise.
Thus, the house is powered by a water supply system with a pressure of 5 to 6 bar. I had to put on a regulator because the idle valve turned on very often.

PS It all started after the steel pipes were replaced with copper pipes in one of the two water risers. During the exchange, I added one additional pipe to the gravity circulation of hot water. Unfortunately, due to the lack of time, this pipe has been blocked in the basement and is waiting to be connected to the boiler. There is probably air in it. Could this be causing the pipes to "knock"?

In my opinion, this is too high water flow velocity in copper pipes. You have to reduce the flow.

And the safety valve was leaking, because you probably do not have a built-in expansion vessel for utility water (this is the installer's error).

a diaphragm vessel at least 18 l should compensate for any pressure fluctuations, and in this closed tube you have an air cushion that works like a compressor at 100%, the reducer acts as a check valve, after closing the tap, the pressure increases, the cushion compresses to expand after a while, water "going back"
shoots the mushroom of the check valve (pressure reducer) and you have a knock

For a 350 l tank, I suggest you use 30 l (e.g. Refix 33D)

Colleagues, thank you very much for your instructions, information. A lot of things were explained that puzzled me.
Yesterday I reduced the pressure on the reducer to 3.2 bar and it is quiet, i.e. the pipes do not vibrate. Another thing I have to do (over the weekend) is to connect the "circulation" to the boiler and get rid of the air from the system.

Thanks again to everyone.

Hello, I will warm up a little cutlet, because in all the threads I read, I have not found any help for me.

My problem: installation in a newly built 3-year-old house. So far everything has been working fine. Symptom: pneumatic hammer - water hammer through the tap in the upper bathroom and at the calf water tank in the boiler room when releasing hot and cold water. Initially, it only happened with a spit in the upper bathroom and the tap where you can hear the knocking sounds - now it is everywhere. Initially, this happened when the water intake was suddenly closed - a tap, a flush or a washing machine. Now it occurs even while the water is running - not always, especially after an hour of water abstraction downtime.

All reverse ports in the boiler room, safety valve have been replaced, the pressure regulator has been inserted (set to 3 bar), the vessel at the reservoir has been replaced, the circulation pump and softener have been checked. Generally, I don't know what else can be done, because after all these exchanges it is louder and some noise than at the beginning.

I would like to add that during this entire period of use, nothing was done during the installation, no changes to the DHW. The underfloor heating works as it should, and the stove is also easy to use.

One more thing that I noticed .. when closing the completely hot water and leaving the cold water no noise.

Some suggestions?

He let you go of the safety valve because you don't have an expansion vessel. Put on a 30 l dedicated to domestic hot water and after the problem.

I had a diaphragm vessel from the beginning, now I have it replaced

Now the question is whether the air is filled with the right pressure. Install a 20 bsr pressure gauge in the cold water area.

There were two plumbers and they said that the pressure in this vessel did not change. A new one was put on with a cold water pressure of 4.5. Later, as it did not do anything, I inserted
Reducer and pressure are set to 3. The vessel nominally has a pressure bearing of 4 bar

I read that with a pressure of 4.5, the vessel should have 4, so it was just that. Symptoms were also present.

I have a pressure gauge on the cold supply .. in total, also replaced with a new one because that something showed twice with the valve open

maniakowy1 wrote:

There were two plumbers and they said that the pressure in this vessel does not change. A new one was installed with a cold water pressure of 4.5. I'll post it later when that didn't work
The reducer and pressure is set to 3. The vessel is nominally pressure rated at 4 bar

I read that at a pressure of 4.5 the vessel should have 4 so that was exactly what it was. The symptoms also disappeared.

I have a pressure gauge on the cold supply.. in total, it was also replaced with a new one, because it showed something strange when the valve was open

I have an identical situation.
Please let me know if the issue has been resolved.

benek0814 wrote:

maniakowy1 wrote:

There were two plumbers and they said that the pressure in this vessel does not change. A new one was installed with a cold water pressure of 4.5. I'll post it later when that didn't work
The reducer and pressure is set to 3. The vessel is nominally pressure rated at 4 bar

I read that at a pressure of 4.5 the vessel should have 4 so that was exactly what it was. The symptoms also disappeared.

I have a pressure gauge on the cold supply.. in total, it was also replaced with a new one, because it showed something strange when the valve was open

I have an identical situation.
Please let me know if the issue has been resolved.

So resolved. It turned out that the expansion vessel was white - as I remember universal, and the pressure in it was set to gas by default. The blue vessels are nominally pumped higher into the water.

So in my case I re-inflated the water pressure to the right value and the problem disappeared.

Well, I had blue ones before, and after a few years it started knocking. I figured it needed to be replaced. I changed it to white on which the pressure is 3 atmospheres. Reducer set to 3.5. I'll get home and try pumping up the vessel to 4 atm and see if it helps.
Thanks for the answer.

Well, the water pressure must be 4 bars, now I don't remember how much I pumped, but I see that they have dishes for sale. Good luck ?

Unfortunately, in my case, raising the pressure on the diaphragm vessel to 4 atmospheres did not help.
When the water in the tank is heated and I run hot water from any tap in the house, I can hear a cyclical clatter.
I wonder if it's not the reducer's fault.
The clattering sound comes from the diaphragmatic vessel, but something must be affecting it.

Or maybe the diaphragm vessel should be of a larger capacity? Currently 8 years old.

Where you have orifices there is noise.