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Is this article a Red Haddock ???
- Thread starter ebee
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Thanks.
For a start, I have never had any dealings with a 3-port ('mid-position') valve, so have never really had any reason to discover how they work - so everything I've said has related to the simple 2-port ones with which I am very familiar. Having now looked, I have learned how the 3-port ones work, as outlined here (seemingly probably from the same source as your diagram):
That's pretty clever [and it subsequently goes on to explain in greater detail]! However, I'm still learning, and, in particular, haven't yet worked out exactly how/why the motor behaves in this way in response to AC/DC.
However, it seems fairly clear that the diode is only there to facilitate the 3-port functionality, so I presume that there is never such a diode in a 2-port one (which, as above, is what I'm familiar with and was talking about). Furthermore, contrary to what Harry suggested (and I couldn't understand), it does not seem that it is the diode which 'causes' the motor to stall - as usual, it seems that it probably stalls because it is (mechanically) stalled, the use of the diode being to determine what position it can stall in. Is that all correct?
It therefore seems as if, always in the case of an 'open' 2-port valve, and also in some situations with with a 3-port valve, the motor is, indeed, 'continuously powered but stalled (mechanically)' - which is the situation which several of us considered to be 'daft', and which presumably has some #negative' consequences.
John - might I suggest you try inserting a diode, in series with a clock motor, and see what happens to the motor?
I presume that it would stop working, as would happen with most things designed to run on AC when they were supplied with DC.
When supplied with DC, the motor would presumably continue to draw current (which would end up as heat) even though the motor was not 'working'. If that's what you meant when you said that the diode causes the motor to 'stall', then fair enough, the only issue then being of semantics/terminology.
However, none of that is relevant to the 2-port valves which I was thinking and talking about (which I presume never have diodes), and nor even to 3-port ones when in the 'heating only' state (when the diode is irrelevant) - so in all those situations we still have the situation of a 'powered but mechanically stalled' motor, which I think most of us are inclined to regard as rather daft?
I have long/lot of experience with our three port actuator problems, and I only ever had a problem with the microswitch failing the once. More often, the problem was the mechanism simply jamming, because the motor power was only just adequate to turn the valve, and at the same time, wind up the spring return. Plastic parts, running against plastic, and brass, in a hot environment, with congealed grease - all under heavy stress from a strong spring.
The MOMO, I now use, was a vastly better design, little stress involved, and no reliance on a spring, and so much less wear.
There is a very knowledgeable discussion of such valves to be found here - https://www.seered.co.uk/sunvic.htm (towards the bottom).
The one problem, the slightly more complex PCB of the MOMO seems to suffer from, is that of water, if the actuator is not mounted above the valve.
I now wish I'd left in my inital line in my previous comment. I it seems you have now changed the goal posts and added time control too.
All 3 of these options off a single point of temperature control:
Suggests a zone solution EXACTLY what you initially described with no mention of TRVs.
Is one TRV on each rad, but paired in some way and working together to create a zone.
Is just one TRV style valve feeding all 3 rads – a system we had in school some 60 years ago on 3" pipes.
Just in case you didn't read or understand it the first time, perhaps you will now.
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Assuming I'm understanding you correctly, I've often wondered why I don't think I've ever seen or heard of anyone doing that.
At least 'domestically', I've only ever seen TRVs attached directly to (single) radiators. However, as I think you're suggesting, I see no reason why the very same devices can't be used 'within pipework' in order to control the flow to two or more radiators. Indeed, implementing that is slightly easier today than it was 'way back' - since, as far as I can see, virtually all TRVs these days come with 15mm² compression fittings for both 'in' and 'out'.
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I have noted the manifolds used with under floor heating, and have wondered if the control heads are interchangeable with TRVs. The Kasa TRV head can connect to a remote temperature sensor / thermostat.
As to if needed is another unanswered question, I know the TRV head can be cooled by an outside wall, so if linked to boiler can turn on the boiler before it is really needed, but as soon as the radiator warms up, a thermal current is started, so the problem of the TRV head being on an outside wall is only there until the heating is running.
So only one of my TRV heads has a problem, as only one is linked to the boiler, the other will not turn on the radiator even if they do open, until the boiler is running anyway. And I have found a wall thermostat in the living room has removed most of my heating problems, my problem was the hall cooled too slowly, and once the thermostats were duplicated, and we had one in the living room as well, the problems seemed to vanish. My problem is my wife puts things in front of the radiators, making it hard to access to charge the batteries in the TRV heads.
I've seen that done in large open, commercial areas. I have also come across, and repaired in similar areas, where they have had a massive (1.5 x 4m) ceiling mounted unit, with a 3ph fan, controlled by a thermostat, and contactor. It was in the entrance to the very large banking hall, supplemented by a single, tiny, radiator on the far wall. Over the years, the temperature in the hall, gradually fell in winter, until it became a problem. As it was located in the busy door, during open hour, no investigation could be tackled during working hours, and the bank wouldn't pay for 'out of hours' except in an emergency - so nothing done, until they arrived at a choice of paying for out of hours, or shutting the bank due to the cold.
I got the go-ahead, to spend a weekend investigating, and trying to fix it. Suspecting the matrix was choked up, I organised a team, and an hydraulic lift to drop the matrix down, out, and round the rear, to give it a flush out. A couple of hours into the task, I discovered the unit was fed via a filter, hidden in the ceiling, which was completely choked. Cleaning that out, restored normal operation. The lift, and the team was completely unnecessary, but there were some very grateful bankers on the Monday morning, when they walked into a warm banking hall.
That doesn't surprise me but, as I said, I've never seen or heard of it being done in a domestic setting - despite the fact that it would seem to be a fairly obvious thing to do if, as per morqthana's situation, one has two or more radiators in one room.
As I said, although it was slightly more difficult io implement in the past (simply requiring and additional fitting or two, it has become child's play now that both ends of TRVs almost invariably have 15mm compression connections.
"should not use a three port valve with a type AC RCD I assume"
I`ve not heard that suggested Eric nor had/heard of any problems with it either.
I`ve not heard that suggested Eric nor had/heard of any problems with it either.
Yes, I also did wonder
As things are, everything in my house has to be satisfied with Type AC RCDs, and nothing seems to be complaining 
Kind Regards, John
Ditto here and also cannot think of any reason why a valve should have this issue.Yes, I also did wonder
Kind Regards, John
Well, I can think of 'the reason' (that when the diode was in circuit, there would be a very large DC component to the current - but I've never heard this being mentioned before (in relation to a 3-port MV) and nor would I lose any sleep over it were it in my house
Why should that trip a type ac RCD or any RCD?Well, I can think of 'the reason' (that when the diode was in circuit, there would be a very large DC component to the current - but I've never heard this being mentioned before (in relation to a 3-port MV) and nor would I lose any sleep over it were it in my house
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