Check valve vs backflow preventer

[ChiefBodie]

My irrigation water is unreliable right now, so I want to plumb and attach my schedule 40 PVC well/drinking water supply to some existing schedule 40 PVC that runs to the sprinklers. The well will serve as a backup to the irrigation water when needed. I will add a valve to isolate the well when I don't want to be using it for this.

I don't want to have contamination in the drinking water, so I need something like a check valve or backflow preventer. In general, what is the difference between a check valve and a backflow preventer? I have noticed a big difference in price. Do they do the same thing?

And, the frost depth is about 12 inches. Are these devices typically installed above or below grade, and how do you protect them from freezing?

 

[gimmodog]

you and your family are drinking this water. I would pay the difference for a preventer to assure myself I am doing my best to drink uncontaminated water. The preventer will be engineered to seal it to prevent a backflow where a check valve may have some leakage.

 

[Industrial Toys]

I'm guessing. A check valve is a very simple (crude) device and probably not as "safe" as the backflow preventer.

 

[gary49]

Use a backflow preventer, more fail safe in that it can drain away water trying to back into the potable system, whereas a check valve cannot. Buy a water meter box and put it underground in that as well as the shutoff and drain valves, if that works for you.

 

[Oldoak]

Use a backflow preventer, more fail safe in that it can drain away water trying to back into the potable system, whereas a check valve cannot. Buy a water meter box and put it underground in that as well as the shutoff and drain valves, if that works for you.

:thumbsup:

 

[RNeumann]

3 types of devices-

Simple check valves literally a little flapper in the line that tries to shut off flow going in the wrong direction. Good for a situation where you are trying to hold pressure (like the vertical pipe in a well) but it isn’t critical for a little leak back. Not a code device for potable water.

Vacuum breaker is a device that is designed and approved to prevent water from flowing in the wrong direction and is approved for potable water. Cheaper than the device below and should be at least 12” above the highest point in the irrigation system.

The final choice is the most expensive but allows for an install below the highest point and meets code. It is called a zone valve. I did a quick search on the Watts site and pulled this one up.

LF99 Lead Free* Reduced Pressure Zone Assemblies, Bronze, Reduced Pressure Zone Assemblies, Backflow Prevention - Watts

Watts and others have all the choices listed above in several models. “Back Flow Prevention” is the term Watts uses.

Some of the anti siphon devices have some frost protection but the bottom line is all of these will need to be protected from freezing.

For code compliance the latter two choices above are needed for most AHJs. But if it isn’t a code job the choice will be yours. The water quality, chemicals used etc should all come into play. Remember, if the failure sucks your irrigation water back into the municipal system and contaminates others your ars is grass. Hint: do the right thing.

 

[Tractor Seabee]

My irrigation water is unreliable right now, so I want to plumb and attach my schedule 40 PVC well/drinking water supply to some existing schedule 40 PVC that runs to the sprinklers. The well will serve as a backup to the irrigation water when needed. I will add a valve to isolate the well when I don't want to be using it for this.

I don't want to have contamination in the drinking water, so I need something like a check valve or backflow preventer. In general, what is the difference between a check valve and a backflow preventer? I have noticed a big difference in price. Do they do the same thing?

And, the frost depth is about 12 inches. Are these devices typically installed above or below grade, and how do you protect them from freezing?

National Model Codes and most local jurisdictions require them also, even on well system that also provide potable water. For irrigation it is a "double check valve" type. It is an engineered assembly. To maintain their integrity in preventing backwards flow of maybe contaminated water an annual test and certification is required. My water district monitors and maintains a log of thousands of BFPs. The county has an ordinance and levies fines for violations. Water systems require them to protect the community from some action you precipitate. In your case being on a well you are protecting your family. If your system has outlets below the expansion tank you are more at risk of an open line creating a vacuum on your system if the pump fails. Anti-siphon devices on every hose bib provides double protection. I have always installed them on mine. Think of you and yours health. Fertilizer in your tea has more than a bad taste. For the nay sayers that say they "have drank water from the same outlet for 70 years with no problem"; there are plenty that will testify to the opposite.

Ron

 

[Tractor Seabee]

3 types of devices-

Simple check valves literally a little flapper in the line that tries to shut off flow going in the wrong direction. Good for a situation where you are trying to hold pressure (like the vertical pipe in a well) but it isn’t critical for a little leak back. Not a code device for potable water.

Vacuum breaker is a device that is designed and approved to prevent water from flowing in the wrong direction and is approved for potable water. Cheaper than the device below and should be at least 12” above the highest point in the irrigation system.

The final choice is the most expensive but allows for an install below the highest point and meets code. It is called a zone valve. I did a quick search on the Watts site and pulled this one up.

LF99 Lead Free* Reduced Pressure Zone Assemblies, Bronze, Reduced Pressure Zone Assemblies, Backflow Prevention - Watts

Watts and others have all the choices listed above in several models. “Back Flow Prevention” is the term Watts uses.

Some of the anti siphon devices have some frost protection but the bottom line is all of these will need to be protected from freezing.

For code compliance the latter two choices above are needed for most AHJs. But if it isn’t a code job the choice will be yours. The water quality, chemicals used etc should all come into play. Remember, if the failure sucks your irrigation water back into the municipal system and contaminates others your ars is grass. Hint: do the right thing.

Someone in a previous post stated to put the BFP in a valve box. Your RPBFP must be place at least 12" above grade. They have a vent that can let contaminants into the system if submerged. Only a Double Check Valve type can be placed below grade. Vacuum Breakers are used two places in irrigation systems: at high points of the system to facilitate draining the system and at hose bibs as a secondary protection for that hose and to allow its drainage w/o disconnecting. Most big box and local hardware stores only carry hose bib anti siphon units and double check valves. I have been rebuilding and expanding an inadequate and non-compliant irrigation system. I put in a strainer, DCVBFP, pressure reducing valve, and drain valve for that manifold, and a vent/gauge connection valve. Have a manual drain at each low point with a vent on the solenoid manifolds. My ground slopes down from the valve assemblies. I have made a deep study of this stuff before starting this my first irrigation system. I have worked with all the mentioned devices in this thread in my steamfitter career so am not a novice in piping systems. BFP are used in a lot of industrial systems. OR, WA, and I believe ID all cite the "Northwest Section AWWA Cross Connection and Backflow Prevention Manual" as their code. No longer have my copy that was thumb-worn.

Ron

 

[ChiefBodie]

Your RPBFP must be place at least 12" above grade. Only a Double Check Valve type can be placed below grade.

I am a bit confused at what can be above vs. below grade, compared to being in the "high spot" of the irrigation system. Here is more about my system:

1. The irrigation piping is both above and below the elevation of my well. The area where I want to make the connection of the well drinking water PVC pipe to the irrigation pipe is slightly below the elevation of the well. So, my connection can never be above the highest spot in the irrigation piping system
2. I get contaminants (bugs, etc.) in the irrigation water supply from time to time. Never any visible contamination in the well water supply.
3. My well consistently applies 50-60lbs of psi in the piping. The irrigation system psi varies whether I am at a high or low spot in the piping. At the area I want to make the connection the irrigation psi is 32psi maximum. (About 10 psi more at the lowest part of the irrigation piping.)
4. I will shut everything down and drain all lines at the end of the season. So minimal frost protection for any above grade components should be OK since I would only be protecting against a surprise frost. Lines will be drained before the coldest temperatures arrive.

The "reduced pressure zone backflow preventer" suggested above is about $800 at Grainger. Or a 1" backflow preventer is about $125 at Lowe's. They look visibly similar but I am guessing the more expensive one must be more capable?

I also found these items for sale online:
1" Watts LF009M2-QT Reduced Pressure Zone Assembly. ($284.14)
Air Gap Drain Fitting #909-AGC (+ $61.80)
1" Brass Wye-Strainer (+ $57.00)

btw, thank you for suggesting the addition of drains and pressure gauges to the manifold.

 

[Industrial Toys]

Weird how there were never such things growing up and people weren't exactly dropping like flies. Helll, people drank out of cisterns!