water pressure question (backflow?)

[Spat]

replies to my mixer shower fitting questions has prompted more. Currently my bath has a mixer tap, hot from tank, cold from mains. If I turn the cold on full (with the hot still on) it runs cold (obviously) but the hot then takes a good while to come back, could this be due to high pressure cold forcing the hot back to the tank, and is this a problem? I was planning to pipe cold from the header tank, is there any alternative so i can use the mains feed, such as pressure equalising valves (such as the ones Screwfix sell), non-return valves etc? Thanks for all help

[AJ]

I think you're required to have double non-return valves in both the hot & cold supplies to the shower, to avoid exactly this potential issue.

[David Hansen]

On 9 Oct 2006 05:24:26 -0700 someone who may be "Spat" wrote this:-

Likely.

Is the shell of your hot water cylinder designed to take mains pressure? Probably not and if that is the case then you run the risk of a spectacular failure of the cylinder one day, with some or all of the contents of the cylinder escaping.

Why would you want to use a main feed?

Whoever installed the mixer did a shoddy job. At the very least they should have put a check valve in the appropriate place.

[Spat]

doesn't sound good, guess I'd better install some check valves. Is an expansion tank required?

It's not a huge issue, but it makes installation of the shower much more convenient as the header tank is a long way from the bathroom and requires some convoluted pipework. The mains feed is obviously right there!

hmm, I suspect the quality of the work is up there with most of the previous owner's diy efforts!

[Aidan]

quality of the work is up there with most of the

Kitchen mixers come in two types. The mains cold & tank hot variety have an internal pipe in the mixer spout, so that the water can't mix within the tap body, for this reason. Dunno offhand if bath mixers are available with this feature.

[David Hansen]

On 9 Oct 2006 07:36:50 -0700 someone who may be "Spat" wrote this:-

Fitted where?

Personally I don't see a great advantage to bath mixers. They generally just take up extra space at one end of the bath. Two taps fill baths just as well, cost less and there are no problems with different pressures.

If one wants a shower over a bath where there is mains cold water then there is a lot to be said for a venturi shower like