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.)

Only if there's some way to build higher pressure outside than in _and_
the valve is open is there any possibility of backflow. Those are
fairly rare circumstances in general--not impossible, but certainly not
all that common.

Yep, probably true.


--
Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral.

- Paulo Freire