anti siphon hose bibs...when?

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Old 07-02-19, 03:30 PM
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anti siphon hose bibs...when?

Showing my ignorance...
I know why an anti siphon is used on an outside hose bib. But what are the conditions that make that a necessary item on some homes but not others? My homes never had the need. But my son-in-law's house , just down the street does have them. Various house on our street have them and many don't. So what conditions need to be met to make it necessary? All the hose bibs are about 6 feet above the inlet on the water supply as they enter the house in the basements.
 
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Old 07-02-19, 04:14 PM
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From, let's call it a strictly functional standpoint, they serve no purpose.The water will flow to the spigot as well as all of the faucets, washing machine, etc. within the home with or without them. And you said that you know why they are used, but for the benefit of anyone else reading along who doesn't know, the term anti-siphon pretty well pegs it because they prevent the water in an outdoor water hose that may be laying in a mud puddle, bucket or whatever from being siphoned back into the water lines within the home. As far as why they are enforced in some instances and not in others, it boils down like many other situations. Why do so many homes have copper pipe sweated with lead core solder. Why is two wire without ground allowed in some homes and other homes are required to have two wire with ground? Grandfathered. In other words, nobody is likely to randomly show up at you home and tell you that you need to install anti-siphon spigots, but pull a permit for renovations, particularly if plumbing is involved, and it's very possible that it will be noted.
 
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Old 07-02-19, 04:37 PM
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Well said pedro, but not quite what I was looking for. In this case the homes on my street were all built at about the same time and all with the current codes at the time (apparently anti siphon was not part of local code at the time). Today a customer came in looking for one because he was getting hose water coming back into the house and contaminating the drinking water. He had a plumber make the suggestion.

My question is what mechanical conditions must be present to cause the back-flow of water? If all the homes were built with basically the same conditions, why did some homes need to install anti siphon? If I leave my hose bibs open when not using the hose will I get a back-flow? My puzzlement is that by definition a siphon draws a liquid from a lower level to a higher level. Or some other type of pressure is pushing it back into the house piping. What I want to know is what piping shape or direction must exist to cause a siphon condition. And if I don't have the condition now, what might I do that I could have the condition?
 

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Old 07-02-19, 04:52 PM
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Say the hose is used and dropped immediately into the mud puddle or bucket of water that I mentioned. Under normal conditions, I agree, and would guess that nothing happens. But have a low water pressure condition related to a bad pump, pressure switch PRV, or whatever, you have a faucet open, then the pressure drops, and you have the potential that it is going to draw water from wherever it is available, in this case, the available water being in the water hose, which in turn, because the end is sealed, creating a vacuum, draws it from that mud puddle or bucket. All very much similar to how a water jet type sump system operates. How much of an issue, I don't know, but suspect that it's not a whole lot different than radon and other things that may be a bit beyond a tad overstated. As for how your customer would know this was the cause of his contamination, well, hopefully it was more than just his plumber's opinion because it seems to me that is would require a fair amount of testing.
 
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Old 07-02-19, 05:04 PM
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You've left the hose on partially open watering your plants. A block away a fire rages at a commercial complex. The fire department hooks up to the hydrants and uses so much water the is a slight negative pressure in your main line. Contaminated water gets sucked up from your yard. Same setting but a water main breaks down the street. negative pressure pulls water into the line.

It not necessarily what you do but what can happen around you. As to why some of your neighborhood has them and some don't maybe some of them have removed or installed them in the past. Some cities/inspectors might require them on a permit job.I know I removed mine the first year I was in my house. They were cheap ones that had a tendency to corrode.
 
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Old 07-02-19, 07:20 PM
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yes the stars and planets would need to align a certain way for that to happen. And its code as far as I know to have some form of backflow prevention.

Also lest not forget most states now put check valves at the meters. So the siphon effect would be isolated to your home when the water is turned off. The check valve at the meter would have to fail and loss of pressure at the main in the street and to have a hose in a puddle in such a way to draw water back up, into the home and to the street.

But I guess it could happen.

And the advent of check valves at the meter now make your home a closed system. Now expansion tanks are required at the water heater the common place. But how many install when they change out the heater? Well how many get permits? HHmmmm... We can go on and on...
 
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Old 07-02-19, 07:20 PM
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pedro's
similar to how a water jet type sump system operates.
and

Tumblers
is a slight negative pressure in your main line.
Gentlemen, that is what I was looking for. Thank you. So I guess it's not so much what your house hold plumbing might be, but instead outside factors or possible inside equipment malfunction.

 
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Old 07-02-19, 07:28 PM
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Our city water dept sent out volunteer questionairres a while back, asking about all sorts of things... do you have irrigation, is it equipped with vacuum breakers, do you have outdoor spigots, are they equipped with backflow preventers, do you have a pool, do you ever apply lawn chemicals by hose, do you ever leave a hose attached to the spigot or is it ever laying in a bucket etc etc etc...

Pretty sure they probably sent follow up letters to people who gave the wrong answers. lol
 
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Old 07-03-19, 12:05 PM
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Backflow has, on occasion, killed people:

The Consequences of Backflow

https://en.wikipedia.org/wiki/Backflow
 
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