3 port motorised valve question

[Tim+]

Is the a power off ?bias? with 3 port valves?

I?ve been idly looking around for ?normally open? two port valves for bypass purposes but they?re relatively silly money due to low demand.

It occurred to me that a three port valve if it has a power off bias could be used as a normally open or normally closed two port valve by blanking off the unneeded port.

Some info I?ve seen on the net suggests that they are spring loaded like a two port valve so that one port will be closed when powered off *but*, I also see that many are advertised as ?mid position? valves which has got me wondering.

What it their normal mode of operation?

Tim

[nothanks]

Does this help?

[Tim+]

Hmm, tells me which of their valves I could use but being a cheapskate I?m really interested to know if this valve would work.

Tim

[Peter Able]

Wow! They ARE expensive. IME three-way valves can be used as a substitute - with a blanking of the third port. They are spring-biassed, so can be used as normally open or normally closed. The mid-position works by limiting the current to the motor and letting it stall (yuk!) half-way through its travel - so neither port blocked off.

Least, that's for the 3-ways I've met.

Bear in mind that the two ports you use are at 90 degrees - so not a simple replace for a two-port.

PA

[Steve Walker]

While not cheap, the Honeywell V4043B N.O. valve is available at around £65 - ignoring all the Ebay ads trying to charge twice that or more. Indeed Honeywell price it at £68 + VAT.

[John Rumm]

Yes they are a spring return valve.

I thought bypass valves were fairly common/ e.g:

See this:

[Kevin H]

3 port valve is biased for hot water only when unpowered.

All you want to know about a 3 port valve (and more) from the excellent John Ward

[Roger Mills]

There are two sorts of 3-port valves - diverter valves as used in W-Plan systems and mid-position valves as used in Y-Plan systems. They both go to the HW position when there's no demand. A diverter valve has only 2 positions - HW or CH. A mid position valve has those same 2 positions plus a mid position where both HW and CH circuits are fed at the same time.

For your purposes you need a diverter valve *not* a mid-position valve. There was a thread recently in which this use was discussed. The valve needs to be inserted between the pump and the other zone valves, with the pump output connected to the valve's input. The valve's normally open (HW) output is connected to the by-pass circuit and the normally closed (CH) output is connected to the inputs to all the zone valves. The valve's motor is connected to the boiler demand so that the heating and/or hot water are fed when there is a demand. When the demand is removed but the pump continues to run during its over-run phase, the pump output will be directed to the by-pass.

[On re-reading this, I realise that I've used the term "is connected to" to describe water connections in some cases and electrical connections in others - but it should hopefully be obvious which is which].

[Tim+]

Indeed. It was just a thought that using a normally open motorised valve would provide better bypass flow without flow noises.

Being normally open the motor would just need to be connected to the ?heat demand? circuit so that it closes whenever the other motorised valves open and automatically opens when they close.

Thanks. If I?ve understood it correctly I should be able to use a mid-position valve (because it looks to be the cheapest option on eBay) as diverter valve with perhaps a bit of minor internal rewiring.

Tim

[Tim+]

Cheers. Not seen that one. I used his wiring guide to rewrite my S plan system yesterday. There was a real rats? nest of redundant wires from a previous boiler which I think which is now tidied up. A very satisfying job!

Tim

[Tim+]

Well ideally yes, but I?m after the cheapest option using a motorised valve. Dunno why a 3 position valve is currently the cheapest I can find but it seems to be. As far as I can tell it will only need minor rewiring to convert it to a diverter valve.

Tim

[Harry Bloomfield, Esq.]

Tim+ presented the following explanation :

Three port spring returns, go to a power off position of open for hot water. The mid-position is where they are part open to both HW and CH ports.

[Roger Mills]

Possibly. In order to drive a mid-position valve to the CH-only position, its CH-on and HW-off inputs both need to be live, so you could probably connect both of these to the boiler demand.

But, because of the complex electronics and internal micro-switches needed to stall the motor in the mid-position (which you don't need) they are notoriously unreliable compared with simple diverter valves. For the sake of a few quid, I would avoid the hassle!

[Harry Bloomfield, Esq.]

Roger Mills laid this down on his screen :

MOMO mid position 2-ports tend to be much more reliable - they don't operate by stalling and there is no spring involved.

[Tim+]

I?m not sure a diode and two resistors qualify as ?complex?.

Well that certainly seems to be true.

Tim