Evil gate valve claims another victim...

[harry]

How can they as there is no zinc in them? Being bronze, the are an alloy of copper and tin.

[John Rumm]

The failure is not caused by lack of zinc. Its a result of them being designed by a moron.

Gate valves fail because the gate recess fills with crap: like hard water scale, magnetite, rust, particulates etc. This makes them harder to close, and also ensures that the gate will not seat correctly, thus letting by.

The extra friction / misalignment on the gate also causes it to jam and get stuck in the recess. The tap mechanism being made from cheese in the first place is then not man enough to withdraw the gate. The spindle snaps internally, and you now have red handled pipe ornament.

This really ought not be a difficult concept for even you to understand?

Now if you live in a soft water area which particularly active water, you may also get non DZR fittings fail due to that factor. However you would expect to see the failures in all kinds of fittings, not just gate valves. Bib taps / stopcocks / float valves etc would also suffer - even your humble compression straight and tee.

Since I have never had to deal with a gate valve in a soft water area, I will pass no further comment on if they are actually more crap than normal in these circumstances. However since under normal circumstances they are crap before you get to worrying about other failure modes, its a moot point.

[harry]

The solution shit-fer-brains is to install it with the handle down. Al valves can be affected by limescale.

[Bob Eager]

I'd love to see you do that on a vertical run.

[John Rumm]

Yeah right...

The one that failed the other day was on a vertical pipe run. How you going to do that Sherlock?

Also why don't you do a quick lap of the country and fix all those millions already installed the "wrong way up".

What kind of dimwit (no need to answer), would install a tap so you can't easily operate it, just in the hope that it makes a bad design less bad, when you could just install a better tap in the first place?

[harry]

If the pipe is vertical, crap can't fall into the recess.

Taper wedge gate valves rarely shut off tight as the angles of the obturating plate and the seat are very difficult to match exactly. So people often overtighten them so overloading the threads. This too can lead to failure.

If the metal looks copper coloured on the failure point, then the problem is de-zincification.

If not, then the problem is overtightening.

[Adam Funk]

Doh. Got it.

[The Natural Philosopher]

Well that (sealing your cold water circuit) is of course OK as far as it goes...until your fsking wife flushes a loo, and opens a tap, and suddenly there is an open valve allowing air into the whole hot AND cold water system and dumping the entire contents of the pressurized hot water tank on your feet.