I'm not sure that motorised valves designed for heating systems will hold back mains pressure. They'll work in pressurised heating systems, of course - but they've then got almost equal pressures on both sides.
They are simply a ball valve turned by a motor. Why would they not hold back that pressure?
Since every single ball valve isolator does.
they may have problems in CLOSING when there is big pressure differential (more than 1.5bar) , but once the outside tap is off, that's not the situation
The ones that were in my old system were not ball valves and only sealed in one direction. They were some sort of swinging wedge that was held against the seat by the return spring.
No they're not, or at least, not the ones I've looked at
Tim
It's not suitable for mains pressure use, and needs the water to enter the common port.
See
Tim
I think that is the way I am going to go. Thanks to you and all others with their comments and suggestions.
I have looked at motorised valves - and it would seem that there is a danger of them "wearing" out. I think I would like to try a simple solenoid type valve
- which is only activated when needed. So - normally closed - apply the power and the solenoid opens. I am guessing that these are different from "motorised" valves which appear to have limited life and a finer adjustment (not just on or off) : or is it just a different name for the same thing?
Any further suggestions/comments on solenoid valves would be appreciated.
(PS I am not actually going to DIY it - I am looking for ideas/components which I can discuss with a professional when I am ready to go)
Again: thanks to all for comments - appreciated.
A motorised valve only takes current while it operates - moves from open to closed or the reverse.
A true solenoid valve would need power all the time it was in one state, or some form of latch mechanism to hold it after it's moved.
Think central locking in a car. At one time this did use solenoids. But these days invariably motors.
Motors are also more efficient than solenoids.
Not generally true for the sort used in heating systems. They have a spring return and close as soon as power is removed. To keep them open, the motor needs to be continuously powered - and simply stalls.
Since the OP wants to feed an outside tap, that will presumably only use water for short periods, so requiring continuous power during 'on' periods shouldn't be a problem.
CH-type motorised valves are not designed for mains pressure, whereas the solenoid valves used on washing machine inlets *are*. A couple of these from a scrap hot & cold fill washing machine would probably do the job as long as you can find a way of connecting them. The ones I've seen have a 3/4" male BSP thread on the inlet side - which is easy to connect to - but the outlet side feeds into a chamber, so it would be necessary to make a housing of some sort with a pipe connector on *its* outlet in order to use the valves in an in-line situation.
It's also not true, in the common case of spring-return motorised valves.
I agree, having checked, that CH valves are no good as one quotes a max differential pressure of 0.7bar
However:
Lists quite a few and one is fine up to 9.8bar.
The other question is: does the OP care if the valve is approved for potable water?
You don't need a pressure difference for a little bit of water to mix. Hot water circuits are not potable, thus permitting slight mixing would not be legal. The reason is that it could set up bacterial contamination of the drinking water feed.
NT
Mine is.
Can't really see why it wouldn't be with a combi.
Is there a clear definition of what is and is not potable?
For example, would you drink water heated by a combi boiler's HW circuit?
Would you drink water from an unvented HW cylinder? I don't think I would.
Single lever kitchen taps worry me a bit - where they mix potable cold water with non-potable hot water. When filling a kettle, you have to make very sure that the lever is in fully cold position. It's much easier when there are separate hot and cold levers.
Do you normally drink hot water?
A storage cylinder is a different thing. Stagnant water and usually from a header tank. Could have been there for ages.
A combi heats potable water straight from the mains. And since you have to run off some water before it becomes hot, likely as 'fresh' as cold.
Some combis do include a storage system to give faster hot water. But probably still safe enough to drink, unless left unused for a long time.
If you are filling a kettle, the water will be boiled. So safe to drink anyway. But plenty do fill a kettle using hot water from a combi.
temperature, materials & protection from contamination are key. HW circuits don't stay in a safe zone temp-wise, nor do they use food grade header tan ks, nor are the headers adequately protected. Hence one sometimes finds a d ecaying dead animal in a header tank.
not if I had another option. It's most likely ok, but unlikely to be food g rade.
no, there's always water between 20 & 60C, low down.
I've come across people that think their HW is potable, but isn't. There's nothing to stop one installing potable HW, but it would take a number of al terations to the usual DHW setups.
NT
Yes. It should be absolutely fine, unless the plate exchanger is leaking. That should be apparently by either pressure loss or pressure gain in the system (1 bar nominal vs several bar for mains and depending if the leak was directional).
Mine comes from an inline electric heater and I drink that from time to time as well as use it for cooking.
When made into tea or coffee, yes. But, to be fair, I would need to raise the temperature above that of the hot tap first.
Yes, maybe filling a kettle wasn't a good example. But what about making a cold drink - e.g. orange squash? If the mixer isn't fully in the cold position, the mixed water could still be cold if the 'hot' bit had been in the pipe for a while - but you could end up drinking non-potable water.
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