Which type of water hammer arrestor?

[Nozzle]

I see there're three types of water hammer arrestor on the market, but which is most effective - and does it need more regular maintenance?

There's the sealed off type with a small diameter piston and an air cushion:

There's the broader squat type with a piston and spring in it (to my mind, more likely to rock about laterally and pass water by the seal):

Or there's the type with a diaphragm and is re-pressurisable when/if so required:

But type is least hassle/works best?

Nozzle

 

[oilboffin]

I've used all these and all ok the White one good for potable water.Bob

 

[Madrab]

Most water hammer can be rectified by mains pressure control, correct pipework runs and support and design and/or valves serviced.

 

[Nozzle]

Thanks for the feedback folks.

The water hammer only started a few weeks back after the guy servicing (repressurising the white expansion vessel) the unvented system had gone. I do get water hammer whether it's hot or cold tap being run though, and only when turning on rather than off. I think it's because there are two pressure regulators the system - one right at the stop cock controlling pressure for the whole house, hard and soft systems, the other is integrated into the relief valve/tundish on the inlet to the cylinder. I think as the valve chatters on the seats of the PRV it is what is causing the hammer. Though as the weeks go on, the hammer is getting less severe and takes longer after the tap is opened to actually start vibrating.

They're all on the same threaded joint anyway, so if one type is duff it'll be easy enough to change out.

Nozzle (edited as I wrote PRV but meant regulator)

 

[Nozzle]

Well, I went for the micro-expansion vessel type - it leaked....

Only slight weeping at the seam between the two halves, but there was/is enough of a drip to damage the LED lighting panel in the ceiling below. Grrr.

It does say rated pressure 15 bar and my regulator is set to 3.5 bar. I recognise that pressures involved with water hammer are many times higher as the pressure wave bounces along the pipe. It does say 'check' pressure in diaphragm every 6 months (obviously I haven't) so there's a chance the bubble has gone.

So now have choice of the other two, piston-in-sealed-chamber types.

Nozzle

 

[Madrab]

.

 

[Madrab]

IMO, you need to find out why it's hammering and sort that, especially if it didn't do it prior to work being performed. If it's one of the pressure reducing valves(prv) then chances are it's the valve's spring that's getting tired and it needs to be replaced (sometimes just manipulating the valves pressure setting from min to max and then back to it's original setting a few times can be enough to reset the spring

The only way water hammer will usually manifest itself is if there is a valve shutting off too quick or it's bouncing due to a loose jumper or a tired spring and that sending shockwaves back down the pipe.

In all but 2 of the cases of water hammer I can remember it's been down to badly fitted/clipped pipework, mains water that needed regulated and/or a valve that needed replaced. I have only ever had to fit 2 arrestor in my time, and they were both down to washing machine valves where the supply pipework was hidden behind a wall and wasn't clipped properly. Obviously they didn't want to buy a new washing machine.

 

[denso13]

I agree with Rob above, in all my years I have never fitted one of those. Always been incorrect installation or pressure/tap/valve/stopcock issues.

 

[Nozzle]

It's the cistern flush, which evidently has a delayed action, but still lightly bangs the pipe once the cistern is full. I can't easily access the service valve (!!!!) to throttle the flow at all.

Nozzle

 

[NicKarla]

Did we actually get an answer as to which one is best/most reliable?
Too much talk on cause. My drier has a horribly aggressive on/off valve which I only found out about after I bought it. Not happy but I’m stuck with it. It’s the only thing that causes hammer so need an arrester. The problem is they don’t seem too reliable.

 

[jurassic sparkk]

Start a new thread please.

 

[RandomGrinch]

My drier has a horribly aggressive on/off valve which I only found out about after I bought it.

If you have an isolator valve on the drier supply, experiment with semi-closing it.
The drier will just draw water for a little longer, but the hammer should hopefully reduce.

 

[Mr.B]

Start a new thread please.

Why does he have to start a new thread when he's only reiterating the original question?

 

[Madrab]

Why does he have to start a new thread when he's only reiterating the original question?

Because things can get confusing when old threads are resurrected, some answer the original post rather than the new question posted and most of 'long in the tooth' pro's on this forum, who can actually answer the questions just skim past it as it's old and it never gets the focus.

Oh and more importantly, it's the forum's policy/rule. All they need to do is raise a new post and link to this one, easy peasy, squeezy lemons ....

Oh and just for completeness, all they need to do is click the 'view results' button to the right of the polling box, though as will be seen there wasn't a lot of feedback, as the proper answer really is to fix the problem and not hide it using something else, as that's just a bit of a fudge.

 

[Mr.B]

OK, I stand corrected.