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redpoint5 02-26-2020 11:42 AM

Backflow Preventer
This seems like a scam. Explain to me why a backflow preventer is so critical that it needs professional annual inspection ($35, which in 2min of work ends up being $1000/hr). How is my sprinkler system that is downhill of the water main supposed to backflow against 40 PSI of pressure? The water in the sprinkler system came from the water main, so at worst it just returns the same water that was already there.

There's about 5 assumptions here that aren't adding up to anything resembling a remotely possible threat.
  • water can flow uphill
  • non-pressurized water can force past a 40 PSI mains pressure
  • A valve isn't enough to stop water flow
  • safe water magically turns dangerous when it enters a sprinkler pipe
  • the backflow preventer and water valve will fail, and annual inspection will remedy this

oil pan 4 02-26-2020 02:06 PM

IDK they're just required.
Remember people who inactive these regs typically have a political science degree, not a plumbing license or engineering degree.

They might be worried someone might try to tie in stored rain water to their sprinkler sys.

roosterk0031 02-26-2020 04:50 PM

I thought the purpose was incase a loss of pressure will create a vacuum in the water system and suck stuff back in, like if someone left a pesticide hose attachment on the hose.

Or a firetruck is attached to a hydrant and causes a drop in water pressure. My dad told me years ago stories of sucking water out of water heaters with the fire truck. Is the PRV on a water heater also a vacuum breaker? I don't know where the air get in to let that happen if it doesn't let it in so it doesn't implode.

We don't have them where I live, no codes pretty much.

oil pan 4 02-26-2020 05:00 PM

It takes about 350psi to explode a waterheater, I do think think a water vacuum will crush it.

redpoint5 02-26-2020 05:14 PM

So it's in case a fire truck is pumping faster than mains pressure can replenish, and if I happen to be spraying pesticides at the same time? There are hydrants in this neighborhood.

Is this a frequent enough problem that we need a solution?

2016 Versa 02-26-2020 07:30 PM

Here's one for you. In KY a home owner has to register water heater purchases made within the state to the state government, be installed by a licensed plumber and go through a state inspection. I live in a double wide mobile home and had a water heater leak in 2016 so I called to find out what all the exact requirements were. Because I live in a manufactured home I could buy a water heater in KY, install it myself and didn't have to have a state inspection. They said if I was ever questioned about the purchase to tell them it was installed in a manufactured home. A plumbing contractor here in town quoted me $1200. for a water heater and to do the install. I bought a water heater for about $350 if I remember correctly and installed it myself in an hour. I live about 25 miles from TN and if I was going to have to pay a plumber $1200. to install a water heater then get an inspection on it I was just going to go to TN buy the water heater, install it and keep my mouth shut. I suspect the reason they don't require a state inspection on a manufactured home is because most manufactured homes come with single element water heaters and wired with 14 ga. wire and most replacement water heaters are dual element units that should be wired with 12 ga. wire. I did mine right, I found a single element heater rather than running a new 12 ga. wire, but I'll bet there are many mobile homes out there that have had the water heater replaced and are not up to code. I guess this is a loophole for the mobile home manufacturers to keep them from having to use 12 ga. that would cost them an extra $ .25 instead of 14 ga. wire and keeps the state from getting their pants sued off when someones house catches fire and burns their family up because the water heater circuit wasn't wired with the correct 12 ga. wire and the state didn't require an inspection. The way my home is set up my breaker box is in the utility room, the water heater is on the other side of the utility room wall in the master bath closet. The difference would have amounted to about 15' of 12 ga. wire vs. 15' of 14 ga. wire. Truth be known mobile homes probably need the state inspection worse than stick built homes.

oil pan 4 02-26-2020 07:34 PM

Most mobile homes aren't up to code

2016 Versa 02-27-2020 01:09 AM


Originally Posted by oil pan 4 (Post 617939)
Most mobile homes aren't up to code

Why am I not surprised? When I lived in NC I lived in a single wide and did lots of work trying to spruce it up a little. Some of the walls were looking pretty bad so I decided to hang wall paper in most of the rooms. I found walls as much as 1 1/4" out of plumb in 7'. About the only way to make the paper look halfway right was to get something with lots of small detail and cut it to fit in the corner. By using a paper with lots of small detail and cutting it right at the corner it wasn't so noticeable that the pattern didn't match up. Anything that had large detail such as large flowers would have stuck out like a sore thumb.

oil pan 4 02-27-2020 11:59 AM

All of our water meters should have a check valve built into them.

redneck 02-27-2020 12:26 PM



What is “Backflow”?

Simply put, “backflow” means that water flows in the plumbing system have become reversed, causing potable water– clean water you can drink– to mix into the used water, which contains bacteria, chemicals, and other harmful contaminants.

Usually, water backflow results from one of two key processes: backpressure or backsiphonage.

Backpressure is a form of water backflow that results from an imbalance in water pressures. The downstream pressure is greater than upstream, or supply, pressure. Essentially, your home or building’s plumbing system contains water at greater pressures than the municipal water mains, which isn’t supposed to be the case. This pushes used wastewater from your plumbing system into the municipal water supply, potentially contaminating potable water. An example might be if you have a large water boiler that’s connected via plumbing with the potable water supply. Without a backflow prevention assembly, high pressure in the boiler could push dirty water into the clean water, contaminating it with sediment and other materials that could make it unsuitable for drinking.

Backsiphonage results from negative pressure, creating a partial vacuum effect. The systems distributing the water fall behind in the system using the water, in terms of water pressures. As a result, a siphoning effect moves contaminated water in the wrong direction. This can happen during a water main break, or in an emergency when a nearby fire hydrant is used (which involves high water pressures).

Backflow preventers are commonly installed in buildings where clean water cross-connects with any of the following installations:

Large boilers. A large boiler can present a backflow hazard when the pressure inside gets too high, pushing the dirty water inside back up into the clean water system.

Irrigation systems. This includes extensive lawn sprinkler systems. Backflow from irrigation systems is hazardous because of the presence of fertilizers and lawn chemicals such as pesticides.

Fire suppression systems. Fire suppression systems can also create pressure differences and siphoning effects that can lead to backflow.
It’s pretty much the same in every state.


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