3 port valves

26 May 2015
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United Kingdom
Does anyone know of a 3 port diverter valve which will take two INPUTS and divert either one of them to the (single) output?

All CH valves I can find take ONE input and divert it to one of two outputs.

I could probably do it with two x 2 port valves wired so that only one or the other is open, but its not as neat as a two into one diverter.

Any ideas welcome.
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don't think that will work. or at least, not reliably. the valve seats in these things are arranged to seal with pressure only on the input side. reversing it would cause leakage round the seats.
I'm sceptical on that, if you look at how a honeywell 2port valve works, when it closes the ball goes against the flow to close.

The 3 port valve works the other way round, so would be equivalent if reversed.

But they're only designed to hold against your average ch circulator (eg ups 15 60) so depends on the pressure in your application.
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Tx Dan but I think they are a tad heavy duty.

A bit more info - I am trying to set up a selector valve arrangement to allow DHW heating from EITHER the engine OR a diesel-fired boiler. Both systems work, but at the moment one is disconnected. Each system has a vane circulation pump and poly header tank (as usual on vehicles). All plumbing is 22mm. Pressure probably 2 bar max.

The problem arises because I want to switch the engine OR boiler to feed the DHW coil. On the return side its easy, as the one return pipe gets diverted to whichever one of the two heaters is providing the heat.
Tx again Dan - but Honeywell installation instructions specifically say:

"The valve MUST NOT be fitted on the return pipework under
any circumstances. Flow from the boiler must be connected to
port AB, the radiator circuit to port A and the hot water cylinder
circuit port B"

They don't, of course, say why. Any ideas?

But the only issue I can foresee is the ball snapping back into position under pump pressure.

Which on a system in a boat will be miniscule so the pump should be on its minimum output.

Remember you're operating out of the original design spec; they're not going to cover all possible uses.
Also says

" It may be plumbed in at any angle but the flow must go into Port AB"

Which kind of precludes its use as a 2-entry valve.
You could always put it on your 'return' which would be topologically equivalent :idea:
Think i'll take one of them apart and see if i can see why they spec as they do.

TVM for help so far. Bedtime now!
As DCaukwell says, you need two two-port valves for this to work properly

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