Hey Allan,
Remember me? :-)
Roy's suggestion of using a float valve at the storage tank to actuate
a pressure switch near the pump can be feasible under the right
conditions.
As William says, you need a valve that will snap shut, not float up
slowly. Here is one that is cheaper than the one he suggests, and made
here in USA:
http://hudsonvalve.com/products.html
I don't see where they describe its snap action, but that's how it was
described to me. I tested one and it did a snappy job. Cheap too.
Next problem is pressure switch. A standard switch like a Square-D or
similar will work reliably down to a setting of roughly 20 PSI cut-
out, from my experience, and an on/off differential of maybe 5 PSI? (I
don't know, but it will work somewhat lower than its rated range).
Anything more sensitive than that may be exotic and expensive. The
pump must be capable of producing sufficient pressure (briefly) to
trigger the pressure switch, whatever switch you choose. If the pump
is a positive displacement type (like the lower volume, high-lift SQF
pumps), then there's no problem producing sufficient additional
pressure to work a standard pressure switch unless the pump is already
working to its limit of pressure.
I've always recommended using a small pressure tank at that pressure
switch (just like in a normal pressurizing system). It absorbs water
hammer and prevents rapid chatter of the switch.
I wish I had some documentation, but I can only say that I've
recommended this method to many customers who had no other good
choice. I know some of them did it, and I never heard of any problems
when done right.
Yours,
Windy
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