Water hammer problem

[DiyNutJob]

Hi all,

My heating system is suffering from a water hammering problem. Every time the pump near the storage tank stops, I get a bang. I understand there should be an air pocket in the pipe-work somewhere that prevents this. I presume I need more air for this pocket. Can someone please give me a clue on what I need to do ?

Here's a schematic of my storage tank and related parts. I am also curious what is the purpose of the shut-off valves at H and I ? I test shut off H and didn't notice anything happening. I am guessing they are for the radiators.

Untitled

• DiyNutJob
• 9 Sep 2013
• 1

Thanks.

 

[45yearsagasman]

I is a system bypass
H is a cylinder balancing valve.

The bypass is adjusted to maintain a minimum water flow through your boiler when TRV's are shutting down the rads when the heating is on

The cyl valve is adjusted so as to maintain a balanced flow through the cyl coil when both CH and HW are calling. A bang when the pump stops is not water hammer (different thing altogether) but may possibly be coming from a component in the cupboard and is not easy to diagnose from behind a keyboard. Hope that answers some of your questions.

 

[DiyNutJob]

Thanks for the details on the valves.

For the pump banging, I don't have anything else in the tank cupboard other than what I have shown in the diagram.

I vaguely remember reading somewhere that when the pump suddenly stops, an air gap somewhere in the pipes stops the rushing water like a cushion. It was said that if the air gap was lost over time, this cushioning effect wouldn't be there and hence resulting in noises.

Is it possible to tell from the diagram which direction does the pump move water, in the upward direction, or downward ?

 

[DiyNutJob]

Posing my above question managed to induce the answer .

The pump pumps water downwards, in M->L->K direction, and the air pocket I am looking for should be located at the top end of pipe f. Am I correct, or have I gone above and beyond as a nutjob ?

 

[45yearsagasman]

have I gone above and beyond as a nutjob

Don't drop your guard like that!
If you have what I'm sure is an open vented system, then pipe f is the flow from the boiler and it will continue up to the exp tank and terminate over the tank with an open end pointing down to the water. That pipe should be full to the same level as is in the tank. It is not a pocket as such. Pipe e is the cold feed and should be completely full of water.
You are imagining your system has an expansion vessel, which it does not appear to have, or need, if its open vented.

 

[DiyNutJob]

Yes, thanks, I do have a vented system. I haven't looked in the loft yet, but I am convinced you are right about pipe e and f because I came to similar conclusions through deduction, although I incorrectly believed pipe f contained an air pocket rather than an open end as you have pointed out.

I guess I will go up in the loft and see if anything is happening there.

The pump is controlled electronically and comes on at unpredictable moments. Is there anyway for me to turn it on and off at will ? Basically I want to reproduce the bang to allow me to better pin point the noise.

 

[45yearsagasman]

It may well be the ball assy inside the 3 port that is causing the single bang.

 

[Dan Robinson]

It may well be the ball assy inside the 3 port that is causing the single bang.

+1

 

[DiyNutJob]

Thanks for the suggestion.

Perhaps a bang is too strong a word. The noise is more of a clack that can be quite loud, and it's definitely a single noise. Anyway, I stuck my head in the cylinder cupboard and listened for it. I couldn't quite fix the location of the noise. But it sounded like from outside of the cupboard and possibly overhead in the loft. I will get some logistics together and lock in the loft.