Period Plumbing - non-return valve

[Flyfisher]

Our outside tap has a non-return valve and, yet again, after a winter of not being used I turned on the isolating valve today only to find that there is no flow through the valve. I took it apart, poked around the innards and got it working for about 10 mins before it stuck (shut) again.

Perhaps I've just been unlucky but before I buy a replacement tomorrow, does anyone have any tips about the type of NRV I should be looking for to get better reliability - if indeed there is much of a choice.

I've seen 'single check' and 'double check' types but don't really know the difference. Mine looks rather like this:

 

[d49xc]

A double check non return valve compared to a single check valve is akin to Tesco's finest range of ready meals and their standard range ...well maybe not.

In reality....
They are two single check valves in sequence, one after the other.
The second check valve in double systems is there to catch the small amount of water that will reverse flow as the first valve is actually in the process of closing - which obviously takes a certain small instant of time - but nevertheless a small amount of water will escape back into whatever is being protected unless the second one is there. So they are the "Rolls Royce" version.

Sorry I don't know much about their innards but I'd expect they are all of the same type now in domestic plumbing sizes.
The older one were of a bulbous nature and contained a simply flap type plate inside them which flapped shut against the reverse flow.
Makesure you get the direction of flow right - it's marked on them.

The intention of these valves is usually to prevent any possibility of the mains being contaminated by 'house water' should the mains fail. If this happens the pressure in the mains pipe would go to near zero and without a non return valves in your system water stored in hoses or just simply in your pipework in the house could/would back flow into the mains as taps are opened beyond you in the system, the mains has now been contaminated.

I thought that all water meters now incorporate a check valve as standard - but I might be wrong on that one and the older ones might not.

 

[Flyfisher]

Well, my "Rolls Royce" version has only lasted two winters, so I'm not overly impressed!

The innards seems to consist of a simple plastic plunger-like valve that seats onto an o-ring, not much to go wrong really but it keeps sticking shut.

Oh well, I'll just fit a new one tomorrow. I hope they are all of the same length so that I don't need to mess about with the pipework!

 

[MdB]

The tap is outside but is the valve? I'm wondering if frost has got to it?

We have something like 6 of them in the house at the moment and I've not had problems with any of them. This is probably due to the 3 bar pressure we operate the system at and that your pressure is a lot less than this.

Just out of interest, is there a long length of pipe between the NRV and the outside tap? If there is, this might be storing high pressure which causes the valve to shut when you flush the loo or similar causing the pressure to drop on the inlet side.

 

[Feltwell]

Might be worth trying not having a seperate valve, but getting an outside tap with the valve built-in?

http://www.toolstation.com/shop/Plu...h+Double+Check+Valve+12+DZR/d20/sd2696/p54792

Mine's been OK, despite being frozen solid every winter for the last 4 years!

 

[Lime]

I suggest that the sticking one-way valve is being damaged by the outside pipe freezing gradually from the tap.
As the ice accumulates in the pipe the pressure within the freezing section will increase far in excess of the mains pressure.
This will force the valve seat tight shut.
The option to avoid this problem is to isolate the tap at it's own stop cock and open the tap to drain.

 

[robgil]

I've been fitting lots of new outside taps lately , those in-built none return valves are rubbish.

Also the amount of people fitting service valves to shut off outside taps is ridiculous, a stop cock is only a few quid more.

In the winter open your tap fully then shut it off via the stop cock. I've actually installed my outside tap inside in the utility room. :lol:

 

[Flyfisher]

I don't think there's a problem with the plumbing arrangement as such, just that the valve has failed. Inside the house there is a lever-operated ball-valve, then less than half-inch of pipe to the non-return valve, then about 10 inches of pipe before going through the wall to the outside tap.

I wrap the outside tap in old towels for the winter but it was so cold last year that it still probably froze. Lime's suggestion about a freezing tap causing reverse pressure to the valve makes some sense because I noticed that the o-ring within the valve was partially visible as if it was being forced past the plastic valve. The ball-valve is definitely turned off for the winter but, though I'd like to think I drained the tap, I can't actually remember.

I'll fit a new one today and be a bit more careful about draining things properly before next winter. Thanks for the comments.

 

[robgil]

You could try boxing it in , it wont stop severe frosts or long periods of freezing weather but you wont get caught out by those surprise frosts we got a few weeks ago.

 

[Onetap]

They don't like the frost, apparently. There was a post on a plumbing forum recently asking about the same problem. There used to be external bib taps with a built-in check valve available, but apparently these were withdrawn because they rarely survived the first winter.

Your picture is a verifiable double check valve, the nut thing can be removed to ensure the first check valve is not letting-by if there is a reverse pressure or for testing or some such thing.

 

[Flyfisher]

I wondered what that little nut thingy was for!

I've just fitted a replacement and all is well, though the real test will be over next winter. We'll see.

I was surprised about the price though. I first went to Wickes as a new store has just opened near us and it was good excuse to have a look around (though I don't know why I bothered when they all look the same!) and they wanted £16.35 for an identical item! I declined their offering and went a few hundred yeards up the road to Focus DIY and bought the same thing for £6.25.

A small difference I could understand but an extra £10 on a £6 item? :shock: And I'd bet it would have been substantially less that £6 if I'd gone to my 'proper' plumber's merchants.

 

[LadyArowana]

I wondered what that little nut thingy was for!

I've just fitted a replacement and all is well, though the real test will be over next winter. We'll see.

I was surprised about the price though. I first went to Wickes as a new store has just opened near us and it was good excuse to have a look around (though I don't know why I bothered when they all look the same!) and they wanted £16.35 for an identical item! I declined their offering and went a few hundred yeards up the road to Focus DIY and bought the same thing for £6.25.

A small difference I could understand but an extra £10 on a £6 item? :shock: And I'd bet it would have been substantially less that £6 if I'd gone to my 'proper' plumber's merchants.

Were they offering a special gift wrapping service as well to account for the price difference? Some beautiful hand printed paper and silk ribbons maybe ? Which reminds me, where is Joce, she hasn't been here for a while :lol:

 

[Flyfisher]

Now there's a thought. There were no silk ribbons that I could see, but perhaps they were offering a fitting service included in the price. :wink:

 

[skier-hughes]

Or Focus are back on their half price sales, having just gone bust again and being in receivership.

 

[Flyfisher]

I did wonder about that but a quick google for 'double check valve' suggests that it's Wickes' pricing that's seriously out of line.