Thermostat N/O and N/C is N/C ever used?

[JohnW2]

I assume that's a 2-port valve ...

That diagram relates to both 2-port and 3-port valves.

... so am I right thinking it has an additional limit switch, not shown, to start the pump and boiler only when the valve is fully open? To avoid risk of them starting when dead-headed if the valve should fail to open.

Yep, there is an additional 'auxiliary switch' (pair of contacts) for switching boiler+pump(s) etc. I presume that the contacts of that auxiliary switch only close when the valve is fully open (i.e. at the same time as the two 'shown' switches operate).

Kind Regards, John

 

[JohnW2]

John, your diagram. It can't be like that or switch 2 would open (as well) as soon as the cam moved.

The 'pull' (as I said, I presume actually 'push') surely doesn't happen (doesn't start) until the cam has moved all the way to the 'fully open' position, at which point both switches will change state.

I think something like this as clearly the diagram does not allow reversal of the motor:...

I'm not sure what you mean - the motor never 'reverses'. Nor do I understand why you have put the two sets of contacts on the opposite sides of the cam - for it to work as I described, they both need to be 'at the same place', so that the cam operates both simultaneously.

I'll try to produce a more realistic diagram, but I might have to hand-draw (scribble) it!

Kind Regards, John

 

[EFLImpudence]

The motor cannot reverse as per that diagram, therefore the valve has to operate by the motor rotating in the same direction.

they both need to be 'at the same place', so that the cam operates both simultaneously.

They could be at the same place, but that would need 180° offset notches, otherwise they would be both on or off at the same time.

There is another relay operated switch for the three port valve. I haven't studied that yet but I suspect that continuously switches off and on to keep the valve in the mid position as do synchronous motor valves.

 

[JohnW2]

They could be at the same place, but that would need 180° offset notches, otherwise they would be both on or off at the same time.

Not if one pair of contacts was 'push for on" and the other "push for off".

As I said, I'll try to draw what I mean. Watch this space.

Kind Regards, John

 

[JohnW2]

As I said, I'll try to draw what I mean. Watch this space.

I don't pretend that it would be engineered quite like this, but this should illustrate the concept (with apologies for drawing and photography!) ....

Kind Regards, John

 

[EFLImpudence]

I think you are right - but it doesn't seem to me the best way to do it.

What happens when the thermostat (controller) changes half way between an operation?

Also, I've just noticed that the valve works by pushing a plunger, not rotating the valve as is usual.
They also have a spring; does this affect anything?


Oh, does hydronic mean anything in relation to the valve?

 

[JohnW2]

I think you are right - but it doesn't seem to me the best way to do it.

I do see downsides, and I think it is only a minority of motorised valves which use this method.

What happens when the thermostat (controller) changes half way between an operation?

I wondered about that, although I imagine it is an extremely unlikely scenario - the 'operation' (i.e. whilst the MV motor runs) is initiated by the thermostat/controller changing state and lasts for a few seconds and I know of few, if any, thermostats which would change state for a second time within seconds. However, nothing is impossible, and should that happen (or should there be a power cut at a critical time), it looks as if the MV motor would stop, and might not start again if one did not manually contrive for the thermostat state to change. However, maybe ...

They also have a spring; does this affect anything?

... might be significant. Does this spring perhaps salvage the situation in the (very unlikely) scenario you mention?

Also, I've just noticed that the valve works by pushing a plunger, not rotating the valve as is usual.

I've never really thought about (or investigated) the type of valve they use, but I probably 'thought' that it was a rotating ball valve. However 'pushing a plunger' is a time-honoured methodology - as used in all traditional taps and stopcocks, and a gate valves are not much different.

Oh, does hydronic mean anything in relation to the valve?

Who knows. It might have the same amount of (non) meaning as many of the highly-scientific-sounding words one hears being thrown about in cosmetic adverts etc The OED say that the word means "Denoting a cooling or heating system in which heat is transported using circulating water." which hardly helps us!

Kind Regards, John

 

[fixitflav]

That diagram relates to both 2-port and 3-port valves.
Yep, there is an additional 'auxiliary switch' (pair of contacts) for switching boiler+pump(s) etc. I presume that the contacts of that auxiliary switch only close when the valve is fully open (i.e. at the same time as the two 'shown' switches operate).

Kind Regards, John

I presume that the contacts of that auxiliary switch only close when the valve is fully open (i.e. at the same time as the two 'shown' switches operate). That's right, for the reason I gave. The reason I asked about the 2-port or 3-port valve was that the only 3-port valves I'm familiar with have a rubber ball covering one port or the other (as I'm sure you know). It's impossible for the ball to cover both ports at the same time, so an auxiliary switch is not needed, the boiler and pump can be started directly, giving simpler wiring (in that respect, at least).

 

[EFLImpudence]

It's impossible for the ball to cover both ports at the same time, so an auxiliary switch is not needed, the boiler and pump can be started directly, giving simpler wiring (in that respect, at least).

...but, for the usual 3 port valves, the ball has to be held in the middle position for both ports to be open, so they do have an additional switch.

 

[fixitflav]

Oh, does hydronic mean anything in relation to the valve?

I don't know, but it's a lovely word!
BTW, I just found how to use Multi-quote.

 

[JohnW2]

That's right, for the reason I gave. The reason I asked about the 2-port or 3-port valve was that the only 3-port valves I'm familiar with have a rubber ball covering one port or the other (as I'm sure you know). It's impossible for the ball to cover both ports at the same time, so an auxiliary switch is not needed ....

Indeed. It's not a 'rubber ball', but iyt certainly looks as if the 3-port version of the Honeywell one we've been talking about canoot have both output ports closed at the same time ...

Having said that, it would seem that the 3-port version, as well as the 2-port one, does have an auxiliary switch/contacts, should one wish to use them for something.

Kind Regards, John

 

[JohnW2]

...but, for the usual 3 port valves, the ball has to be held in the middle position for both ports to be open, so they do have an additional switch.

As I've just written, the Honeywell ones certainly do have such an additional switch, but, as I also implied, I'm not sure what it would be used for.

With a 2-port valve, one usually uses that auxiliary switch to switch the boiler and pump on when heat is called for and the valve opens. However, with a 3-port valve, unless there is an 'off' position (both output ports closed), the position of the valve does not tell one whether anything (CH and/or DHW) is/are calling for heat, so I don't see that the auxiliary switch could be used to control the boiler/pump.

Kind Regards, John

 

[EFLImpudence]

This is getting too complicated because these valves are not 'normal' like the ones in central heating.

Whilst the valves in the picture (just diverter valves) are 3 port valves they apparrently cannot have all three passages open at the same time - as 'normal' ones when central heating and DHW heating is required at the same time.

 

[JohnW2]

This is getting too complicated because these valves are not 'normal' like the ones in central heating. Whilst the valves in the picture (just diverter valves) are 3 port valves they apparrently cannot have all three passages open at the same time - as 'normal' ones when central heating and DHW heating is required at the same time.

Indeed - they are diverter valves, not 'mid-position' ones. As I said, I don't really understand what use one would make of the 'auxillary switch.

As a slight tangent, whilst we are discussing this topic, can anyone explain to me how the traditional 2-port motorised valves (with a synchronous motor and a auxiliary contacts) actually work, since I've never really understood ...

... what happens when the motor has fully opened the valve, but still has power applied (until the requirement for heat ceases and the controlling voltage is removed)? Does the motor 'stall', but still continue drawing current? - or does it keep turning (against some sort of 'slipping clutch') - or what? I have several MVs in my system, all of which have been in service for just over 30 years and, if I recall correctly, I have only once had to replace the motor in one of them. However, if they were spending long periods 'stalled' or working against a 'slipping clutch' I would have expected much poorer survival than that.

Kind Regards, John

 

[EFLImpudence]

http://wiki.diyfaq.org.uk/index.php/Motorised_Valves