Reliable isolation valves?

[acone]

Hello,

I've three isolation valves in the airing cupboard. The two that are on piping attached to the hot water cylinder (flow and return to the boiler) seem to start leaking after a few years causing damage to floor/ceiling etc. They are full bore 22mm valves that look like https://flowflex.sharepoint.com/siteimages/P472NPFB.gif but mine have '22mm PN40 W0G' stamped on one side and a 'B' in/on a 'V' stamped on the other side.

Since the last time these valves where changed they haven't been touched but started dripping from around the screw head. I assume that these valves have some kind of rubber seal in them and they just deteriorate overtime from the high heat and expansion/contraction of metal(?)

So my main question, is there a better make/brand or type of isolation valve that I can replace these with that are more reliable and won't leak around screw head turn area? Is there some kind of rating etc that I can look out for?

Also could I have them removed entirely, do I really need them? However I have noticed that the plumber who fitted the last pair hasn't left the two valves on the pipes to the cylinder fully open (i.e. screw slot not parallel to piping). Is there a reason why he would restrict the flow to the hot water cylinder?

Thanks in advance.

 

[Madrab]

They have a nylon/PTFE seat that the ball sits in, that doesn't quite expand and contract at the same rate as the metal does, that can then create gaps and the valve can then leak. Only thing you can really check for is WRAS & BS (EN) compliance but TBH that doesn't really guarantee anything.

I use Pegler full bore lever valves and only used on the cold feed to the cylinder and so far no complaints.

Not sure why you have them at the cylinder on the flow and return from/to the boiler unless for servicing of the cylinder, it is a fully pumped system? Can you add a pic?