David Nebenzahl wrote:
On 10/3/2008 10:24 AM dpb spake thus:

David Nebenzahl wrote:

By the way, after testing it I could see why these are good things
to install: after turning on the hose bib and letting the hose reel
fill up, I closed the bib, whereupon a large gush of water sprayed
out of the anti-siphon valve. Had it not been there, all that water
would have gone back inside the house plumbing, along with whatever
crap was in the hose (or in a pool the hose was thrown into, in
some cases).

How would that be if the the bib is close?

Right; duh. I should have written that *some* of that water *might* have
gone back inside the house. (A closed hose is basically a small
reservoir of water under pressure.)
....
But there's no pump there to build more pressure than the supply
pressure that filled it, hence no reverse flow.

If it is left out in the sun expansion will, of course build pressure,
but that is a very small volume even if the bib is subsequently opened
and the feed pipe is already full anyway. In very small volume any that
does manage to flow inward will be flushed immediately the hose is
opened and an open valve in the house would have to be in pretty special
location to cause the water in a stub supply line to be pulled inwards.

It's just not a common event imo...again, possible, granted but hardly a
major concern.

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