SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

Hi: Hope you are planning to install a reduced pressure backflow preventer to prevent your stock tank from contaminating your homes potable water supply. This needs to be instralled above ground. Check out the following sight for more information. http://www.irrigationtutorials.com/backflow-preventers.htm

Sorry to preach, but this is a safety issue for your family and community, and although you may have already planned to add this, others reading this post may not be aware of the potential dangers of cutting this essential piece of equipement trying to do a system the cheapest possible way.

Thay said, now an idea

One idea, is making the tank the only feed to the system. Use it with a fertilizer solution when your plants need nutrients. Fill it with water when you wish to water. Fill the tank from the top, assuring the water from the hose is well bove the tank, causing a large air gap. You can use continual feed irrigation bhy using a 1/4 strength solution in the tank at all times, so the plants get a continual dose of diluted fertilizer...fertigated. Easy to use thje chweapes clock and vaalve you can get. Check manufactures websites to make sure the valves will perform under low pressure/llow volume. Sprinklerwarehouse.com (swite sponswer) has som battery powered DIG brandas that should do nicely. Clock is included for about $35.

How is that for cheap. Just makke sure the water feeding the tank can not get into the water supply filling it (hose from spigot)

Glad you fopund the information helpful. I don't know all the possibilities that can cause backflow, but I sure wouldn't want to take a chance. Especially if it contaminated th well. Big and expensive whoops. Anyway, enough of a sermon.

I am not a pump guy. Others would be better at helping you. However, I think you could still use the tank idea with a float switch. Don't know, I' more of a low volume guy.

Good luck. Jeff

Quoted from "pazpazon"

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Yes I will surely get a backflow prevention device, if necessary, although, if the water spigot is closed when fertilizing from stock tank, how would the water flow back into the house system?

Luckily, I only use organic fertilizer, no chemicals, but I still don't want any of that running into my pipes.

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Backflow is one of those things lots of people have a hard time understanding how it can happen. I know of people who have (foolishly) installed an irrigation system with NO backflow, reasoning that water only flows out of the system, and the water can't flow backwards through a "CLOSED" valve. Unfortunately they are wrong. Things can happen, especially with city water, where something causes a sudden drop in system pressure (think line break) and suddenly the pressure of the water in your pipes is greater than the pressure from the system. That will cause water to flow back towards the city system. When this occurs, even water on the far side of an irrigation valve can get sucked back into the system. After all, these valves are designed to hold back water flowing towards the yard. When back pressure like this occurs, it's like the valves are installed backwards, and water can and will get siphoned back into the system.

At www.irrigationtutorials.com, there is a pretty lengthy discussion on various arguments for various forms of backflow. The simplest summary of those arguments I would like to highlite for the situation in hand is this... If your irrigation system is feeding water ONLY to your lawn, then any backflow preventer (your local building codes allow) are fine. If you are adding something to that water, then ONLY the RPZ (Reduced Pressure Zone) Backflow preventers are considered acceptable. The main reason is becaue the way they are designed, they will prevent backflow even if the internal check valves fail. (The only exception is if the entire RPZ becomes submergged, hence they must be installed above ground). A duel check valve backflow preventer (by contrast) offers no backflow protection if the internal check valves fail. All it takes is some trash in the line, and even city water will get trash in the line (I've got a 200# filter on my city water supplied irrigation system, and I've seen some of the stuff that has gotten filtered out of city water)

Bottom line, when you start getting into fetilizing with an irrigation system, "I will surely get a backflow prevention device, if necessary" doesn't cut it. An RPZ is required to insure drinking water doesn't become contaminated (and they are not cheap, especailly if local building codes require a certified plumber install it, as some do).

As to HOW it can happen, the bottom line is if all the parts are connected, backflow and contamination can happen. Even if you have manual valves to only allow fertilizer or city water to be the source, it only takes human error to have both open at the same time when something that causes backflow to occur. Plus, if fertilizer is flowwing through irrigation pipes, residue from the fertilizer will get left in the pipes. So even when the fertilization system is disconnected from the system, backflow can occur sucking in that residue.

Since you said you were looking for a "cheap" solution, these are the reasons why Jeff suggested a system where the fertilizer is the only source for the irrigation. Let me restate his suggestion to make sure I know what you are both saying...

You want an irrigation system sometimes feed from city water, sometimes feed via a pump from a fertilizer tank. Jeff's suggestion was to ALWAYS feed the system via a pump from a fertilizer tank. To avoid the cost of a backflow preventer, you in effect, fill the tank with water with a hose or pipe suspended above the tank. As long as there is a gap 3 times as high as the source pipe is wide, that air gap makes for a backflow preventer with the same level of protection as the RPZ. Basically, you could design a system where city water feeds the tank with an automatic valve that turns on when water levels in the tank are too low and turn off when the level is high enough (think of the water suppl for your toilet). So as long as the pipe feeding water to the tank is about 3"-6" above the tank, worst case senario, it is physically impossible for fertilizer to get back into the water supply regardless of human error of mechanical breakdown (and no RPZ).

Quoted from "pazpazon"

Thanks very much for the reply, Jeff..

Yes I will surely get a backflow prevention device, if necessary, although, if the water spigot is closed when fertilizing from stock tank, how would the water flow back into the house system?

You do not get to make any judgements when it comes to code compliance. Either comply, or face the consequences.
In the case of the blending of a town water supply and a fertilizer tank, you will install a Reduced Pressure Zone device in the town water line feeding your sprinkling setup. These cost money, but it beats having your home condemned. (and trust me, the authorities can do it in a heartbeat, with all the law on their side, and you and your evicted family finding themselves in a motel room, wondering what happened - Do not become an example of just how bad this sort of thing can get)
Now, strictly from the land of the cheap, there is the old "air gap" backflow prevention. Think of a bathtub spout filling the bathtub. The spout is higher than the rim of the tub, and that height difference is your air gap. That loses all your city water pressure, and obligates you to use a pump to supply pressure, but your pump and tanks and fertilizer will have no physical connection to the city supply, so what you do with it won't be an issue.