> >>
>> >> >> >>
>> >> >> Take a look at the Grundfos PumpPlan.
>> >
>> >---8<---
>> >
>
>> >> There are also some design notes. One thing they do show is that
>> >> the pump goes on the flow side of the boiler. Since there are
>> >> non-return valves, this is probably not optional.
>> >
>> >Surely the pump has to be on the flow side since it has common input,
>> >separate outputs, nothing to do with the valves - or am I missing >> >something?
>> >
>> It could have been installed on the return backwards with a combined
>> output, but the valves would prevent that.
>
>I don't see what you mean: if you combine the output you've
>effectively got one pump, haven't you? (Can you ascii art it?)
It was the way you had it drawn with the pumps on the return side, IIRC. The flow came from the boiler and split to the CH and DHW. The returns from these came to the twin pump and then the combined output went to the boiler.
In reality, the pump needs to go on the flow side, so the boiler flow goes to the common point of the pump. Then one pump output goes to the CH and the other to the DHW. The NR valves prevent flow from each circuit back towards the boiler. The returns from the circuits combine and go the the boiler.
>
>> >> If the boiler is of a type where heat is produced continuously, having
>> >> a pump with a sprung loaded valve could be a problem if the pump >> >> fails.
>> >
>> >Only as much of a problem as if a motorised valve fails - ?
>>
>> Motorised valve can fail open and does hav a spring to ensure that. >
>I thought the spring normally kept the valve shut (on a 2-port valve).
>On a 3 port with the valve off and the pump on I have seen let-by. >
>
>Anyway, it'd be the same problem as if the pump fails in a
>conventional setup.
I'm not so sure. The pump will let by and I was thinking of gravity circulation. With a sprung NR valve that won't happen.
However, it's academic since the boiler doesn't need it and likely shuts down in absence of electricity anyway.
>Your move ;-)
>
>
>cheers
>
>Stan the Span
.andy
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