1 00:00:00,560 --> 00:00:03,600 Speaker 1: Welcome to brain Stuff from house Stuff works dot com 2 00:00:03,600 --> 00:00:08,080 Speaker 1: where smart happens. Hi Am Marshall Brain with today's question, 3 00:00:08,600 --> 00:00:12,520 Speaker 1: what is an anti siphon valve? If you live in 4 00:00:12,560 --> 00:00:15,800 Speaker 1: a house with a built in lone sprinkler system, there's 5 00:00:15,840 --> 00:00:19,960 Speaker 1: a device called an anti siphon valve or a backflow 6 00:00:20,079 --> 00:00:23,520 Speaker 1: prevent in your yard. What is this thing for and 7 00:00:23,600 --> 00:00:26,880 Speaker 1: how does it work? Andi siphon valves are a great 8 00:00:26,880 --> 00:00:30,360 Speaker 1: example of how building codes evolved. They also show how 9 00:00:30,360 --> 00:00:33,120 Speaker 1: the code can contain rules that seem to make no 10 00:00:33,240 --> 00:00:37,920 Speaker 1: sense but actually solve significant problems. Most building codes now 11 00:00:38,000 --> 00:00:41,880 Speaker 1: require ati siphon valves in several different places in a house, 12 00:00:42,280 --> 00:00:47,560 Speaker 1: including all external hose connections, outdoor sprinkler systems, and sometimes 13 00:00:47,640 --> 00:00:51,680 Speaker 1: even in toilet fill valves. First, let's define a siphon. 14 00:00:52,200 --> 00:00:55,920 Speaker 1: A siphon is any pipe, pose or tube that's used 15 00:00:55,920 --> 00:00:59,640 Speaker 1: to move a liquid from higher locations to lower locations. 16 00:01:00,200 --> 00:01:03,120 Speaker 1: To use a siphon, you fill the piper hose with 17 00:01:03,160 --> 00:01:05,800 Speaker 1: the liquid and you stick one end of the pipe 18 00:01:05,840 --> 00:01:09,160 Speaker 1: into a liquid at a higher location. Then you let 19 00:01:09,200 --> 00:01:12,440 Speaker 1: the liquid start draining at a lower location. As the 20 00:01:12,480 --> 00:01:15,319 Speaker 1: liquid drains out of the pipe at the lower location 21 00:01:15,440 --> 00:01:19,160 Speaker 1: of vacuum develops that sucks the water from the higher location. 22 00:01:19,720 --> 00:01:22,880 Speaker 1: Gravity and suction do all the work, so no pump 23 00:01:23,000 --> 00:01:27,600 Speaker 1: is required. You can use siphons to drain ponds, empty barrels, 24 00:01:27,600 --> 00:01:31,640 Speaker 1: remove gasoline from gas tanks, et cetera. Now think about 25 00:01:31,680 --> 00:01:34,399 Speaker 1: your yard. Let's say you take a garden hose and 26 00:01:34,480 --> 00:01:37,840 Speaker 1: you stick it into a three gallon barrel that you 27 00:01:37,920 --> 00:01:40,560 Speaker 1: have in your yard. When you turn on the water, 28 00:01:40,760 --> 00:01:44,400 Speaker 1: you fill the hose with water. As the barrel fills, 29 00:01:44,480 --> 00:01:47,160 Speaker 1: the end of the hose inside the barrel gets covered 30 00:01:47,200 --> 00:01:51,640 Speaker 1: with water. Now imagine that the water pressure fails, for example, 31 00:01:51,680 --> 00:01:55,040 Speaker 1: because someone opens a fire hydrant and significantly lowers the 32 00:01:55,040 --> 00:01:58,200 Speaker 1: water pressure on your block. What will happen is that 33 00:01:58,240 --> 00:02:00,840 Speaker 1: the water in the barrel will siphe been back through 34 00:02:00,880 --> 00:02:04,200 Speaker 1: the hose into your water system. So the next time 35 00:02:04,240 --> 00:02:07,880 Speaker 1: you turn on your kitchen sink, you're drinking water out 36 00:02:07,880 --> 00:02:10,959 Speaker 1: of that barrel. Yuck. And the problem is even worse 37 00:02:11,040 --> 00:02:14,000 Speaker 1: if you're using the hose to fill a pesticide tank. 38 00:02:14,400 --> 00:02:17,600 Speaker 1: In the case of a lawn irrigation system, if there's 39 00:02:17,720 --> 00:02:20,800 Speaker 1: standing water in the yard when the siphon effects starts, 40 00:02:21,000 --> 00:02:24,359 Speaker 1: it can suck fertilizer, weed killers, dog poop, and all 41 00:02:24,400 --> 00:02:27,400 Speaker 1: sorts of other things into your home's plumbing. That's a 42 00:02:27,480 --> 00:02:31,320 Speaker 1: double yuck. The anti pipheon valve prevents all of this. 43 00:02:32,120 --> 00:02:35,080 Speaker 1: The anti piphon valve is nothing more than a one 44 00:02:35,160 --> 00:02:38,320 Speaker 1: directional valve. It can be as simple as a spring 45 00:02:38,400 --> 00:02:41,720 Speaker 1: loaded flap that lets water flow in only one direction. 46 00:02:42,280 --> 00:02:45,200 Speaker 1: A key thing to note is that many people skip 47 00:02:45,280 --> 00:02:48,200 Speaker 1: the anti pipe valve. Either they don't know about it, 48 00:02:48,280 --> 00:02:50,640 Speaker 1: or they don't understand it, or they think it costs 49 00:02:50,680 --> 00:02:52,960 Speaker 1: too much, or they simply don't like the idea of 50 00:02:53,000 --> 00:02:55,920 Speaker 1: being told what to do by the building code. In 51 00:02:55,960 --> 00:02:59,440 Speaker 1: the process, they endanger their own health and the health 52 00:02:59,480 --> 00:03:02,640 Speaker 1: of their name. Merse because there's an actual problem that 53 00:03:02,720 --> 00:03:06,360 Speaker 1: the anti sifon valves solves. That's why there are building 54 00:03:06,440 --> 00:03:10,600 Speaker 1: codes and building inspections. Do you have any ideas or 55 00:03:10,639 --> 00:03:13,840 Speaker 1: suggestions for this podcast? If so, please send me an 56 00:03:13,840 --> 00:03:17,080 Speaker 1: email at podcast at how stuff works dot com. For 57 00:03:17,160 --> 00:03:19,440 Speaker 1: more on this and thousands of other topics, go to 58 00:03:19,480 --> 00:03:23,120 Speaker 1: how stuff works dot com.