Speaker 1: Welcome to brain Stuff from house Stuff works dot com
Speaker 1: where smart happens. Hi Am Marshall Brain with today's question,
Speaker 1: what is an anti siphon valve? If you live in
Speaker 1: a house with a built in lone sprinkler system, there's
Speaker 1: a device called an anti siphon valve or a backflow
Speaker 1: prevent in your yard. What is this thing for and
Speaker 1: how does it work? Andi siphon valves are a great
Speaker 1: example of how building codes evolved. They also show how
Speaker 1: the code can contain rules that seem to make no
Speaker 1: sense but actually solve significant problems. Most building codes now
Speaker 1: require ati siphon valves in several different places in a house,
Speaker 1: including all external hose connections, outdoor sprinkler systems, and sometimes
Speaker 1: even in toilet fill valves. First, let's define a siphon.
Speaker 1: A siphon is any pipe, pose or tube that's used
Speaker 1: to move a liquid from higher locations to lower locations.
Speaker 1: To use a siphon, you fill the piper hose with
Speaker 1: the liquid and you stick one end of the pipe
Speaker 1: into a liquid at a higher location. Then you let
Speaker 1: the liquid start draining at a lower location. As the
Speaker 1: liquid drains out of the pipe at the lower location
Speaker 1: of vacuum develops that sucks the water from the higher location.
Speaker 1: Gravity and suction do all the work, so no pump
Speaker 1: is required. You can use siphons to drain ponds, empty barrels,
Speaker 1: remove gasoline from gas tanks, et cetera. Now think about
Speaker 1: your yard. Let's say you take a garden hose and
Speaker 1: you stick it into a three gallon barrel that you
Speaker 1: have in your yard. When you turn on the water,
Speaker 1: you fill the hose with water. As the barrel fills,
Speaker 1: the end of the hose inside the barrel gets covered
Speaker 1: with water. Now imagine that the water pressure fails, for example,
Speaker 1: because someone opens a fire hydrant and significantly lowers the
Speaker 1: water pressure on your block. What will happen is that
Speaker 1: the water in the barrel will siphe been back through
Speaker 1: the hose into your water system. So the next time
Speaker 1: you turn on your kitchen sink, you're drinking water out
Speaker 1: of that barrel. Yuck. And the problem is even worse
Speaker 1: if you're using the hose to fill a pesticide tank.
Speaker 1: In the case of a lawn irrigation system, if there's
Speaker 1: standing water in the yard when the siphon effects starts,
Speaker 1: it can suck fertilizer, weed killers, dog poop, and all
Speaker 1: sorts of other things into your home's plumbing. That's a
Speaker 1: double yuck. The anti pipheon valve prevents all of this.
Speaker 1: The anti piphon valve is nothing more than a one
Speaker 1: directional valve. It can be as simple as a spring
Speaker 1: loaded flap that lets water flow in only one direction.
Speaker 1: A key thing to note is that many people skip
Speaker 1: the anti pipe valve. Either they don't know about it,
Speaker 1: or they don't understand it, or they think it costs
Speaker 1: too much, or they simply don't like the idea of
Speaker 1: being told what to do by the building code. In
Speaker 1: the process, they endanger their own health and the health
Speaker 1: of their name. Merse because there's an actual problem that
Speaker 1: the anti sifon valves solves. That's why there are building
Speaker 1: codes and building inspections. Do you have any ideas or
Speaker 1: suggestions for this podcast? If so, please send me an
Speaker 1: email at podcast at how stuff works dot com. For
Speaker 1: more on this and thousands of other topics, go to
Speaker 1: how stuff works dot com.