Check Valve Query

Let you drain water from between the two check flaps?

I have wondered that... Something to do with the assembly?

Dont really know but would guess to turn on/off the flow.

Never heard of such a thing :)

That would be my guess. I was tempted to take one out and see if the innards fall out. But it could possibly take some effort to make it leak proof again.

That has always been what I thought it was for, although I've never opened one up to see.

I think I read somewhere it's to allow testing that both valves are working (given a "double check valve" will appear to work even if one of the two is buggered). But I'm buggered if I can remember or find where.

Unless you can access the mid-point, you can't prove both valves in a double-check valve are working, and they are normally only fitted where the regs require the use of a double check valve. Also for draining, but you mustn't fit them outdoors where they might freeze, as that instantly wrecks them.

What about the taps sold for outside hosepipe use with built-in double check valves? Are they not at least a bit frost resistant?

Oh...

Bugger!

What I didn't say in my first post is that this check valve, although inside the bungalow under the kitchen sink, is connected by a short stub of pipe through the wall to an outside tap. Since the cold snap, the tap only dribbles. At first I thought it was still frozen, but it must have thawed out by now and I would expect a decent flow. I suspect that short stub froze for part of its length, and as you say, wrecked the check valve. OOI when you say 'wrecks', does that mean it no longer stops back-flow, or that it just stops all flow, like mine? I suspect I know what you'll reply!

Funny you should mention this. Just went to hose the dog down and water only trickled out of the tap. I didn?t realise that it had an inbuilt check valve until I looked closely and spotted the tiny hex head screw underneath.

Haven?t had a chance to disassemble it yet but is seems like the check valve must be the problem.

Tim

Well here's the problem. The non-return valve has been forced back through an orifice that it's not meant to fit through resulting in it jamming.

Fortunately very easy to sort, just rip out all the non-return crap and it works better than ever.

Of course it's no longer compliant but I reckon it's hoses that need non-return valves rather that taps.

Tim

Sounds like what's happened to mine. The whole idea of non-return valves on outside taps strikes me as questionable. If there's going to be a significant negative pressure in the water main to suck back contaminated water from the hose or whatever, that negative pressure will also suck contaminated water in through all the myriad of leaks that the water companies have been urged to stop, over the decades, not just this last week.

Does it come out when you remove the hex head screw? That would answer the other question!

The hex screw is only for draining water out between the tap washer and the non-return valve. Presumably we?re all supposed to shut off the supply internally and the drain the tap down via the hex screw. Simpler if you have an internal shutoff valve to just leave the tap open

All in all, I think built in non-return valve in outside taps were an ill thought out idea.

Tim

Water regs required the non-return valve to be indoors back in

That?s as may be, but loads of outside bib taps come with double check valves built it, just waiting to cause problems after a heavy frost/freeze.

As I said before though, logically the double check valve should be *after* the tap, not where it can cause problems in the event of a freeze before the tap.

Tim

Was it just the flap or whatever is the moving part of the valve, or the entire innards? If the latter, presumably you now have a nice smooth wide bore bit of brassware obstructing not very much. :-)

I just drilled and ripped out all the plastic parts. As you say, it now has a smooth wide bore.

Tim