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Feed valve

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cadec
cadec Member Posts: 8
in Plumbing
Can someone please explain to me the correct location for the boiler fill valve, again is it to be in the location of the expansion tank (zero pressure change) before circ or can it be on the return side bottom of boiler. I have been having this argument with some and been told I'm wrong just really want to know if there are pros and cons to either side Also we , Mostly due pumping away, but always have the fill in the bottom of the boiler on the return side.


Thanks

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  • Jamie Hall
    Jamie Hall Member Posts: 23,327
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    I can't see much practical difference.

    Assuming that the valve is always open -- a somewhat dubious assumption

    If the valve is at the location of the expansion tank, the expansion tank -- location of almost zero pressure change -- the feed valve will see only very small variations in pressure, and the expansion tank lowest pressure (system cold) will be whatever the valve is set for.

    On the other hand, if the valve feeds at the return side of the boiler, and the pump is where it should be, pumping away, then there will be slightly more variation in pressure depending on just where the return is in relation to the pump and the tank. Particularly if the sequence is valve, boiler, tank, pump, then the valve will operate so that the pressure at the inlet to the boiler will be whatever the valve is set at, and the system off pressure may be somewhat higher by the pressure difference across the boiler.

    And if there are no leaks in the system... it will make some difference in the system operating pressures as related to the feed valve setting, and the difference, IMHO, is purely academic.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Zman
    Zman Member Posts: 7,569
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    To the best of my knowledge it is best installed near the expansion tank. The reasoning is that the circulator can influence the valves ability to accurately sense system pressure.

    This possible problem would be at it worse with a circ pumping into the expansion tank and away from the valve. In this case the valve would see artificially low pressure when the circ turns on and add water to system that does not need it.

    As far as putting it where you described, as long as the boiler has relatively low resistance to flow, I don't see why it would be a problem. I guess if some meat head added a bunch of cold water to a hot boiler, it could cause some thermal stress?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    SWEI

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