Many thanks. That answers my question, then ....
... which, as I said, makes me somewhat amazed that nearly all of mine have lasted 30+ years despite spending much of their time in a 'stalled' (but powered) condition.
On the 3-port valves I'm familiar with, on the Honeywell W-plan, DHW preference, no mid-position, the valve motors when CH is called (and DHW is satisfied) and stalls at end of travel as long as CH demand lasts. The motor must be built to stand it; it is highly geared to the valve shaft so I guess the power is very low, though the data sheets I have don't give a figure. I haven't studied the circuit for the mid-position valve in detail, but I think the motor stops in mid-position, but still stalls when CH only calling.
They might be built "to stand it" but that's obviously relative - and I remain surprised that nearly all my MVs have survived for so long (30+ years) despite being stalled (but powered) for so much of the time. As I said, as a matter of curiosity I think I'll do some measuring of current/power - watch this space!
Albeit my experience is limited, I don't think I've ever met a 2-port one which does not have a spring return (hence presumably 'stalls').
Just remembered I have a spare head for a mid-position valve (it's a long story!), and on that it says 230/240v AC 50hz motor 5 watt. I assume that is worst case, presumably when stalled, so that's not going to do much harm. It will pick up a lot more heat from the hot body below.
Indeed - that's the mechanism (cams and all!) we've been talking about for the past couple of days.
I wouldn't necessarily count on that. When only one current or power figure is given in the spec/labelling of a motor, it is usually the 'running' current/power - not 'start-up' or 'stalled'. However, given that this is, unusually, a motor which is intended to be stalled for much of the time, you could be right - but, as I said, I wouldn't count it it. I'll try to do some measurements as soon as I have a moment.
Every half-turn - but, yes, that's what we've been talking about - but I personally haven't ever 'met' one of them!
The one of which I posted a diagram seems to fall into that category - it looks as if (although not a 'ball' mechanism), both ports would be (partially) open during the transition.
To which diagram are you referring?
Those (that one) doesn't turn; it plunges.
OK - done, with a Honeywell V4043H spring-return 2-port valve, and I'm rather surprised by the answers ...
Indeed it does.
I think that depends upon the exact arrangement, and exactly what it is that is 'turning', doesn't it? As you go on to say/illustrate ...
With those such as in your photo, as you say, there will be relatively little 'rotation' of the control spindle. The exact angular movement will depend on the length of the control arm, the diameter of the ball and the distance between ports, but it will certainly be less than half a turn, and quite possibly less than quarter of a turn.
It does, but you were contradicting fixitflav in post 67.
I was talking about (as I also thought fixitflav was) a 'rotating' set-up like we discussed yesterday (per my scribbled drawing of the cam etc.) - and that does require half (not quarter) of a turn (at least of the cam - we didn't discuss how that related to angular movement of the valve mechanism) from open to closed.
Just noticed this post. That's right for the mid-position valve, but the additional switch is to stop the motor at mid-position. I meant a switch to start the pump and boiler, for safety reasons. The either/or valve, with body style as your #70, doesn't have either switch.
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