WEBVTT - What is an anti-siphon valve?

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<v Speaker 1>Welcome to brain Stuff from house Stuff works dot com

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<v Speaker 1>where smart happens. Hi Am Marshall Brain with today's question,

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<v Speaker 1>what is an anti siphon valve? If you live in

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<v Speaker 1>a house with a built in lone sprinkler system, there's

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<v Speaker 1>a device called an anti siphon valve or a backflow

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<v Speaker 1>prevent in your yard. What is this thing for and

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<v Speaker 1>how does it work? Andi siphon valves are a great

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<v Speaker 1>example of how building codes evolved. They also show how

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<v Speaker 1>the code can contain rules that seem to make no

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<v Speaker 1>sense but actually solve significant problems. Most building codes now

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<v Speaker 1>require ati siphon valves in several different places in a house,

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<v Speaker 1>including all external hose connections, outdoor sprinkler systems, and sometimes

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<v Speaker 1>even in toilet fill valves. First, let's define a siphon.

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<v Speaker 1>A siphon is any pipe, pose or tube that's used

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<v Speaker 1>to move a liquid from higher locations to lower locations.

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<v Speaker 1>To use a siphon, you fill the piper hose with

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<v Speaker 1>the liquid and you stick one end of the pipe

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<v Speaker 1>into a liquid at a higher location. Then you let

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<v Speaker 1>the liquid start draining at a lower location. As the

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<v Speaker 1>liquid drains out of the pipe at the lower location

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<v Speaker 1>of vacuum develops that sucks the water from the higher location.

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<v Speaker 1>Gravity and suction do all the work, so no pump

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<v Speaker 1>is required. You can use siphons to drain ponds, empty barrels,

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<v Speaker 1>remove gasoline from gas tanks, et cetera. Now think about

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<v Speaker 1>your yard. Let's say you take a garden hose and

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<v Speaker 1>you stick it into a three gallon barrel that you

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<v Speaker 1>have in your yard. When you turn on the water,

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<v Speaker 1>you fill the hose with water. As the barrel fills,

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<v Speaker 1>the end of the hose inside the barrel gets covered

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<v Speaker 1>with water. Now imagine that the water pressure fails, for example,

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<v Speaker 1>because someone opens a fire hydrant and significantly lowers the

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<v Speaker 1>water pressure on your block. What will happen is that

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<v Speaker 1>the water in the barrel will siphe been back through

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<v Speaker 1>the hose into your water system. So the next time

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<v Speaker 1>you turn on your kitchen sink, you're drinking water out

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<v Speaker 1>of that barrel. Yuck. And the problem is even worse

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<v Speaker 1>if you're using the hose to fill a pesticide tank.

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<v Speaker 1>In the case of a lawn irrigation system, if there's

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<v Speaker 1>standing water in the yard when the siphon effects starts,

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<v Speaker 1>it can suck fertilizer, weed killers, dog poop, and all

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<v Speaker 1>sorts of other things into your home's plumbing. That's a

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<v Speaker 1>double yuck. The anti pipheon valve prevents all of this.

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<v Speaker 1>The anti piphon valve is nothing more than a one

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<v Speaker 1>directional valve. It can be as simple as a spring

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<v Speaker 1>loaded flap that lets water flow in only one direction.

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<v Speaker 1>A key thing to note is that many people skip

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<v Speaker 1>the anti pipe valve. Either they don't know about it,

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<v Speaker 1>or they don't understand it, or they think it costs

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<v Speaker 1>too much, or they simply don't like the idea of

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<v Speaker 1>being told what to do by the building code. In

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<v Speaker 1>the process, they endanger their own health and the health

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<v Speaker 1>of their name. Merse because there's an actual problem that

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<v Speaker 1>the anti sifon valves solves. That's why there are building

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<v Speaker 1>codes and building inspections. Do you have any ideas or

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<v Speaker 1>suggestions for this podcast? If so, please send me an

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<v Speaker 1>email at podcast at how stuff works dot com. For

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<v Speaker 1>more on this and thousands of other topics, go to

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<v Speaker 1>how stuff works dot com.