A friend wants to install a warm water tap for dog washing outside.
The problem is he has gravity hot water & mains pressure cold. Can thermostatic blending valves cope with the pressure difference?
Additionally, do they provide protection against back flow to the HW system?
Tim
Orifice plate in cold supply? (I.e. a corrosion resistant "washer" with a small hole in it). It will probably be a fairly small hole, maybe 2 mm? Would make sense to add non return valves into both supplies. Use either ball valves or proper stop valves on the supplies, not the cheap gate valves as sometimes found around hot water systems because these may not seal completely.
Do non-return valves have a low enough flow resistance to not seriously impede a gravity fed supply?
Tim
You could try a thermostatic shower specially for a combi or multipoint water heater. These include a pressure equialisation valve on the inputs, and are very fast acting (so that a change in load on the hot water won't momentarily scald or freeze you). Unfortunately, these are much more expensive than the standard wax pellet type thermostatic mixer.
The valves will not be designed to survive freezing outside though.
Some do, they are basically a non-return valve on each input, and a single on/off/flow rate valve on the output. Trouble is that with gavity feed, you will lose a lot of the pressure/flow inside a non-return valve.
Check the minimum acceptable pressure for any valve you buy, against the height of the water head from the storage tank.
No problem, I?d be fitting it indoors underneath a sink
It looks like this would do the job although the question about unbalanced pressures isn?t addressed on the website. I?ve posted a question.
In article <q2hrpk$f9h$ snipped-for-privacy@dont-email.me, Andrew Gabriel snipped-for-privacy@cucumber.demon.co.uk> writes
If you are taking the cold directly from mains is not a non return valve mandatory? If your friend is not in a bungalow I would have though his hot water pressure from the loft would easily overcome any resistance in the mixer. After all they do work upstairs in the bathroom.
I have a manual mixing arrangement in the garage for just the same purpose. I have a spare gravity shower unit but haven't got round to fitting it yet - well it's only 10 years since we switched to mains fed hot water. I have rigged up a test unit and it handled the mains pressure OK.
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