Evil gate valve claims another victim...

Does that mean they should be replaced with something else if the opportunity arises? We have a few in the HW/CH system. They've not caused any problems yet, but I haven't needed to turn them yet.

I was wondering that. Surely, most systems are pressurised these days?

Same way really - poke one in the outlet of the CH header, and the other into the CH primary vent.

You then turn off the both rad valves, and crack the nut on the valve union to the rad to allow the rad to be drained. Then you undo the valve connection to the pipe. Since you have no route for air or water to get into the system you have a hydraulic "lock" which will prevent much if any water coming out of the now open rad tail.

They are typically fine until you go to use them. So I guess if they fail then, the opportunity has presented itself ;-)

Mr Pounder should already know this. He claims to have worked on big ships.

On a pressurised system, it can't be enough just to depressurise it, can it?

So long as the rads are all well bled, then yes - once de-pressurised its no different to a vented system with the vent and F&E pipe closed off.

The reason they typically fail is dezincification of brass components. In many situations bronze/gunmetal valves should be used which do not dezincify.

Cowboy plumbers fit the brass ones for cheapness or ignorance. Plenty of ignorance in this group including the OP.

Well, for some reason, I seem to have to drain the CH more than one might think is strictly necessary. Probably because I end up replacing old leaky radiator valves whenever I decorate - and I've decided to always chase the radiator pipes into the wall from now on, which usually means they need to be lengthened a bit. I'm just thinking - next time it's drained, maybe I should replace the valves?

Thanks. The valves in our HW/CH are probably something like 30 years old. Do you suppose they will have the marks on them that the article mentions?

What is the 'valve gate party trick' to which the OP refers? I might need to make use of it one day.

I did expand that in the op... its not a trick one plays on gate valves, but a trick they play on you!

i.e. When you attempt to turn them off, they will frequently fail to seal completely (due to the presence of debris / sludge / hard water) in the gate recess - so you often end up with a trickle of water still letting by the valve. Then when you attempt to open the valve again, the spindle may snap internally before it withdraws the gate from its recess, leaving the gate closed, and the hand wheel turning endlessly, but not actually doing anything.

You will have to excuse harry, he has delusions of competence (presumably influenced by using lots of nice large shiny commercial gate vales in industry, and naff all experience of the crappy things sold for domestic plumbing).

Using DZR fittings in situations where they are not required is unlikely to solve this particular problem which is a result of a basic design problem, and the valve type being unsuited to applications where they are infrequently used. (Also on older installations DZR fittings were unlikely to have even been available at the time of installation)

(The requirement for DZR is dictated by local water conditions and also in some cases installation conditions. The local water authority can normally advise if the water will tend to attack normal brass fittings. Its a problem that usually only arises in soft water areas. Local conditions may include fittings that will be in contact with soil (e.g. if a pipe were unprotected and buried).

Oh, right. I thought you were referring to a trick you could use to get one last operation out of them, after which you'd need to replace them ASAP.

We do have soft water. So less prone to some problems, but more prone to others.

Would be nice, but alas no. Once they have snapped, there is nothing sensible you can do to fix them in place.

Yup soft water tends can be more corrosive in general, but obviously free from scale - which can be a mixed blessing. On the negative side, hard water will deposit scale, and require more detergent etc, although on the plus side it tastes batter, and sometimes the scale is handy (e.g. sealing pinhole leaks, or coating the inside of lead pipes so they are less able to contaminate the water).

Drivel. Using incorrect valves in any situation is down to ignorance, idleness and/or greed. You seem to be one of them.

The crooks installing these cheap brass valves are ripping people off and get away with it because it takes a few years for the damage to be done/become apparent.

DZR valves have been available for fifty years to my knowledge. The problem is with the cowboy plumbers we have these days with an NVQ or some such drivel.

ok then, just delusions?

Well at least you seem to now accept that gate valves are "incorrect valves" - so that is progress.

That does not even make semantic sense.

Well the one I replaced the other day was not installed recently, and likely 40+ years old. Typical failure mode though. So I guess the "crook" that installed it is not too fussed (if even still alive).

DZR gate valves fail in exactly the same way, and for the same reasons as "normal" ones.

If zinc leaching is a problem, you would expect to see it in all the brass fittings, not just gate valves. Dezincification is a non issue with our water anyway.

Perhaps, however A crap DZR valve is no better than a crap normal brass valve in cases.

Mind your spurs on the carpet...

Organic carrots are fine. That's what I used.

Organic ones are much harder than ones dosed with nitrogen, so don't break off and leave an awkward bit stuck at the bottom of the cold tank,

Well that didn't happen on the Ice Patrol Ship Endurance. It very nearly sank south of the Falklands in 2008.

From Wiki :-

The Royal Navy inquiry found that the flood happened while a sea-water strainer was being cleaned, in an attempt to improve the production of fresh water. The air lines controlling a hull valve were incorrectly reconnected, resulting in the valve opening and an inability to close it. (i.e arse about face). /end

No-one on board had overall charge (or knowledge) of all the systems and documentation provided with the Norwegian built (and previously leased) ship was either inadequate, non-existant or just plain incorrect (or in Norwegian).

The Entire fleet of Class 45 warships have such inadequate duplication that they cannot operate in hot humid conditions. So not much use in the Gulf or Caribbean then.

Looks too simple to work! ;-)

How do those work for changing radiator valves? It seems to me you're still going to spray water between unscrewing the old valve & getting the bung in, & again between removing the bung & screwing the new valve together.

They are not primarily intended to be used on the rad tails themselves. They are used in vented CH systems to block of the Feed & Expansion connection to/from the CH header tank, and also the CH vent pipe over the tank. Once that is done, you have created an air lock that makes it harder for water to escape.

So say you wanted to change a rad valve, you would stick the plugs into the expansion tank/vent pipe, and then turn off both rad taps. Now drain just that rad. Uncouple the valve you want to change from the rad, and now you can remove it from the pipe. You will get a small amount of spillage - but the whole system will not be able to drain out of the open pipe, because its sealed and air can not enter elsewhere to let the water out.