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Sprinkler Gurus: Backflow Preventers and Water Pressure
Posted on 5/14/25 at 1:29 pm
Posted on 5/14/25 at 1:29 pm
One of my sprinkler lines sprung a leak. I closed the valves at both backflow preventers.
Got my guy out to repair the leak. But when he turned them back on, the pressure was extremely low.
Thoughts?
Got my guy out to repair the leak. But when he turned them back on, the pressure was extremely low.
Thoughts?
3
Posted on 5/14/25 at 4:29 pm to RanchoLaPuerto
quote:
Thoughts?
Remove backflow preventers? I don't understand their purpose in a pressurized water system.
Recently removed mine because they are annoying
Posted on 5/14/25 at 9:07 pm to RanchoLaPuerto
Is it a vacuum breaker you’re talking about? If so they get clogged all the time. Might need a new one. I just had this happen and decided to ditch it. I agree with the other guy, I don’t plan on leaving my hose laying in a ditch to siphon contaminated water.
Posted on 5/15/25 at 8:51 am to RanchoLaPuerto
If its one head, there's probably dirt in the head. If its one zone, there's probably dirt/crud in the zone valve. If its the whole system, there's dirt/crud in the spring or check valve of your backflow. You can google how to clean out a PVB which is what I'm assuming you have since its for a sprinkler system. There are very few parts inside and normally you just have to take it apart and let water run through.
Posted on 5/15/25 at 9:08 am to Motorboat
The purpose is for when your pressurized water system becomes depressurized. Whether its a break in the line or the city shut your supply off to do a repair etc. etc. I'm not harping on them, I think they serve a good purpose that benefits the water supply system as a whole, but I think its insane what they tried to pull last year making every business (in EBR) install one by a certain date.
At a minimum the city should've subsidized 1/2 the cost for everyone as the business owners receive no benefit from protecting the water supply and still had to foot the entire bill.
The reason they are important on sprinkler systems is because the heads are below grade when not running and dirt/debris from the yard or fertilizers or herbicides can easily travel backwards into the municipal water supply without one. If the sprinklers aren't isolated by a backflow, anytime water is used there is potential for the water to be drawn out of the sprinkler lines and into the lines that serve the city or your house.
Its a 1/100,000 chance that someone leaves their hose in a bucket of herbicide and walks away at the same time Bubba cuts into the water main but you spread that out over an entire city or state and you have instances of morgue "fluids" backflowing into water supply or 2-4-D contaminating an entire parishes water supply because the farmer left his sprayer filing while he went to get diesel. You will probably never be the one to commit the frickup, but having BFP's installed everywhere acts as a fail safe for the lowest common denominator.
At a minimum the city should've subsidized 1/2 the cost for everyone as the business owners receive no benefit from protecting the water supply and still had to foot the entire bill.
The reason they are important on sprinkler systems is because the heads are below grade when not running and dirt/debris from the yard or fertilizers or herbicides can easily travel backwards into the municipal water supply without one. If the sprinklers aren't isolated by a backflow, anytime water is used there is potential for the water to be drawn out of the sprinkler lines and into the lines that serve the city or your house.
Its a 1/100,000 chance that someone leaves their hose in a bucket of herbicide and walks away at the same time Bubba cuts into the water main but you spread that out over an entire city or state and you have instances of morgue "fluids" backflowing into water supply or 2-4-D contaminating an entire parishes water supply because the farmer left his sprayer filing while he went to get diesel. You will probably never be the one to commit the frickup, but having BFP's installed everywhere acts as a fail safe for the lowest common denominator.
Posted on 5/15/25 at 10:04 am to MrBobDobalina
quote:
The reason they are important on sprinkler systems is because the heads are below grade when not running and dirt/debris from the yard or fertilizers or herbicides can easily travel backwards into the municipal water supply without one.
What are the physics of this in a pressurized system???
Dirt would have to flow backwards against pressure, through the sprinkler line and valves and get into the system, again against pressure.
ETA: I have one on my system, but it is required due to local regulations. My thought is that some manufacturer of back flow valves went around convincing local water boards that they were absolutely necessary to pad their sales.
This post was edited on 5/15/25 at 10:07 am
Posted on 5/15/25 at 10:58 am to bbvdd
Full disclosure I am not an engineer/physicist just a plain jane degree and a good bit of experience with backflows. It can happen 2 different ways, back pressure and back siphonage.
When your sprinkler system is not in use, it is at static city pressure. A BFP isolates the drinking water from the sprinkler water like a check valve (that's all they really are is over built, enormous check valves), it will stay at the same PSI until you turn on your sprinklers. Without a BFP, the two systems are "cross-connected" and technically water can flow back and forth from the city piping, into your residential piping, back into city piping indefinitely.
In the situation above with no BFP installed, the water in the sprinkler system has no way to exit the system, sprinklers aren't running. The city sends you water at let us say 65 PSI, it only achieves this maximum pressure at 3 in the morning when very low demand is on the water supply system. When you, your neighbors, and the apartment complex down the street from you use water (peak demand hours), the city's water pressure drops to a lower PSI (say 55 psi) than the sprinkler system was at when it rested overnight at low demand hours. This water in the sprinkler system will flow backwards due to the pressure differential until it catches air and "burps" itself, or until the pressures equalize. Anything near those sprinkler heads (think fertilizers, pesticides, pet fecal matter) has the potential to be drawn into the piping and sent backwards into the city supply. This gets magnified enormously if the city water supply system goes offline (for repairs or a water main blows out) or experiences significant drops in pressure during peak demand.
You can get in the weeds with backflow and find examples that blame it on the venturi effect from pumps going off line or breakages allowing suction to draw water into the piping system. I like to paint a simpler picture. Water in pipes (especially under pressure) can behave very different from how you might expect under a particular set of circumstances, these are only installed to remove the risk from those special circumstances.
TLDR BFPs act as check valves that can introduce air into the piping system to relieve back pressure or back siphonage from the side that they were installed to protect.
When your sprinkler system is not in use, it is at static city pressure. A BFP isolates the drinking water from the sprinkler water like a check valve (that's all they really are is over built, enormous check valves), it will stay at the same PSI until you turn on your sprinklers. Without a BFP, the two systems are "cross-connected" and technically water can flow back and forth from the city piping, into your residential piping, back into city piping indefinitely.
In the situation above with no BFP installed, the water in the sprinkler system has no way to exit the system, sprinklers aren't running. The city sends you water at let us say 65 PSI, it only achieves this maximum pressure at 3 in the morning when very low demand is on the water supply system. When you, your neighbors, and the apartment complex down the street from you use water (peak demand hours), the city's water pressure drops to a lower PSI (say 55 psi) than the sprinkler system was at when it rested overnight at low demand hours. This water in the sprinkler system will flow backwards due to the pressure differential until it catches air and "burps" itself, or until the pressures equalize. Anything near those sprinkler heads (think fertilizers, pesticides, pet fecal matter) has the potential to be drawn into the piping and sent backwards into the city supply. This gets magnified enormously if the city water supply system goes offline (for repairs or a water main blows out) or experiences significant drops in pressure during peak demand.
You can get in the weeds with backflow and find examples that blame it on the venturi effect from pumps going off line or breakages allowing suction to draw water into the piping system. I like to paint a simpler picture. Water in pipes (especially under pressure) can behave very different from how you might expect under a particular set of circumstances, these are only installed to remove the risk from those special circumstances.
TLDR BFPs act as check valves that can introduce air into the piping system to relieve back pressure or back siphonage from the side that they were installed to protect.
Posted on 5/15/25 at 11:14 am to MrBobDobalina
The above would be an example of back pressure.
For the same situation as it would pertain to back-siphonage, imagine your sprinklers are now running on a timer when you aren't home. The city water main blows out 3 blocks away from you. The entire water supply system just experienced a huge surge of negative pressure as every house, business, or any building with water was at 65 psi, and now has 0 PSI. There is a humongous amount of suction on the water supply system as it tries to equalize pressure as quickly as it can. Since your sprinklers were running, they are now acting as siphons that will inhale anything near them until pressure is equalized.
The examples seem so far fetched that they would never happen, and for all intents and purposes they will probably never happen to you. But it happens all the time, all over the place. They exist because ice cubes with pet poo and grass showed up in someone's freezer 8 days after maintenance was performed on a water line. Or because blood from the morgue that was in a clogged sink got sucked through the spray hose meant to wash the area down. Or because Jimbo at the plant has been working 16s for longer than he can remember and he accidentally tied the cold water line for the new hose bibb into the return line for the chiller since he was on auto pilot.
They will trap the contaminants to one side of the BFP without allowing that contaminated fluid to return to the water distribuition system.
For the same situation as it would pertain to back-siphonage, imagine your sprinklers are now running on a timer when you aren't home. The city water main blows out 3 blocks away from you. The entire water supply system just experienced a huge surge of negative pressure as every house, business, or any building with water was at 65 psi, and now has 0 PSI. There is a humongous amount of suction on the water supply system as it tries to equalize pressure as quickly as it can. Since your sprinklers were running, they are now acting as siphons that will inhale anything near them until pressure is equalized.
The examples seem so far fetched that they would never happen, and for all intents and purposes they will probably never happen to you. But it happens all the time, all over the place. They exist because ice cubes with pet poo and grass showed up in someone's freezer 8 days after maintenance was performed on a water line. Or because blood from the morgue that was in a clogged sink got sucked through the spray hose meant to wash the area down. Or because Jimbo at the plant has been working 16s for longer than he can remember and he accidentally tied the cold water line for the new hose bibb into the return line for the chiller since he was on auto pilot.
They will trap the contaminants to one side of the BFP without allowing that contaminated fluid to return to the water distribuition system.
Posted on 5/15/25 at 12:01 pm to MrBobDobalina
The utility company’s meter likely has a double check valve or similar backflow preventer to keep you from contaminating the city’s water supply. If your irrigation is connected to the domestic supply line to your house, it should be isolated with a backflow preventer to keep you from contaminating your own domestic water. Water can most definitely siphon out of your irrigation main into your house. I’ve had hot water siphon through a janitors sink fixture to where multiple rooms in a building had 100 degree water coming out of the cold water supply piping.
Posted on 5/15/25 at 12:35 pm to T-Jon
While that is probably true for most places, Baton Rouge Water Company employees tasked with the install are usually about the cheapest and most under qualified members of society you could imagine to be trusted with the sanitation/ preservation of a healthy water supply. The dual checks they (sometimes) use are pocket sized and are quite prone to failure. They also are unable to be tested or repaired. That difference separates BFPs (which are referred to as assemblies) from Dual checks which are classified as devices and do not provide proper prevention for backflow. Dual checks are buried underground while BFP's live above ground with us. They can't do their job without exposure to atmospheric pressure.
It is important to note that there is a BFP assembly that is called a DCV or Double Check Valve that is most commonly used on fire suppression systems to prevent rusty sprinkler water from ending up in your coffee pot at work.
Dual check, roughly the same size as a tube of chapstick:
Double Check Valve, range from about 18" long up to 4 feet long in commercial buildings and can weigh upwards of 200 pounds.
I promise I'm not on the bad guys' side. I don't care if you install them or not. But they absolutely serve a purpose and do it very well (when reasonably maintained.) They're required on any new commercial building for that reason.
I 100% disagree with retroactively making people install them and foot the bill entirely like what has happened here over the past year. We pay taxes and pay the water company enough money that this could've been rolled out much more smoothly over a longer time frame and proper compensation should've been paid to anyone that was made to install them retroactively. The end user sees no benefit from installing one, only the water supply system as a whole.
It is important to note that there is a BFP assembly that is called a DCV or Double Check Valve that is most commonly used on fire suppression systems to prevent rusty sprinkler water from ending up in your coffee pot at work.
Dual check, roughly the same size as a tube of chapstick:
Double Check Valve, range from about 18" long up to 4 feet long in commercial buildings and can weigh upwards of 200 pounds.
I promise I'm not on the bad guys' side. I don't care if you install them or not. But they absolutely serve a purpose and do it very well (when reasonably maintained.) They're required on any new commercial building for that reason.
I 100% disagree with retroactively making people install them and foot the bill entirely like what has happened here over the past year. We pay taxes and pay the water company enough money that this could've been rolled out much more smoothly over a longer time frame and proper compensation should've been paid to anyone that was made to install them retroactively. The end user sees no benefit from installing one, only the water supply system as a whole.
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