One isolating valve on both loft tanks inputs?

[phloaw]

Hi, just after the mains stopcock under my kitchen sink I have a tee, one pipe to drinkable water+washing machine and the other to the loft cisterns (talking about an open vented pumped S-plan system, standard here in UK).

I was wondering whether it is safe to add an isolating valve on the latter pipe, placing it right after the aforementioned tee (i.e., under the kitchen sink).

I am asking because I've read somewhere that the feed and expansion tank shouldn't have a valve on its input, but I couldn't find a consensus on that, online.

I am also suspicious because currently I have an isolating valve just before the bigger loft tank in the loft, not serving the FE tank. Which could be a hint that FE shouldn't have an input valve?

[Chippo1]

I put full bore ball valves all over the place , can’t see any reason for not , but then I am not a plumber!

[chrrris]

There's no problem with having an isolation valve on the cold-water supply to the F&E tank for maintenance. The problem (and this is probably what you've read about) is with having a valve on the expansion pipe itself -- that's definitely not acceptable as shutting it off would effectively create an explosive situation.

As Chippo1 says, full bore lever valves are fine (as long as they're not on the expansion pipe) and definitely preferable to gate valves, which are the work of the devil!

[Chippo1]

Chrrris , I don’t think of the expansion tank on a pressurised system , mainly because my system is open vented due to a lack of incoming water pressure and volume.

I stick ball valves in all over makes any maintenance a doddle not having to drain tanks etc. So they are on the supply to and from tanks and many other places throughout the plumbing. Also having refurbished my bungalow myself bits of pipe work were preinstalled early on and often sat for months until I got to finished that job, so an accessible ball valve makes life easy. So for instance in the loft for the hw and cw supplies to the kitchen sink there are valves as well as the valves ultimately fitted under the sink next to the tap, same goes for the washing machine and dishwasher supplies

[chrrris]

Chrrris , I don’t think of the expansion tank on a pressurised system , mainly because my system is open vented due to a lack of incoming water pressure and volume.

It was open vented systems I was referring to. Specifically the bit marked red in this picture (sorry about the rubbish drawing!). There was a classic example of this in my sister-in-law's house when she moved in. Someone had chopped off the loop over the F&E tank and fitted an automatic air release valve (I'm guessing to try to "fix" a botched shower pump install that was pulling air in from the vent pipe). Air could escape, water couldn't. Basically, it was an explosion waiting to happen. It wasn't me who spotted it -- it was a guy she'd got in to quote to replace the system with a combi boiler. I heard him swearing from the loft when he saw it though!

You do also occasionally find isolation valves on the vent pipes between the cylinder and the H/W feed (the green bit in my drawing, where a valve would actually be okay), especially where the pipework has been modified to add feeds to extra bathrooms. They're equally dangerous. Everywhere else though (e.g. the cold water supply to the F&E tank, the hot feed (the green bit in my drawing, onwards) is no problem.

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[Chippo1]

Yep understand where your coming from , valves on mine would not shut off the vent.