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!

 

[Gary Fowler]

You have been given the options and now you must decide if your families health is worth the expense of a $300 back flow preventer that is Code Compliant for municipal water districts or if you want to go cheap with a check valve system. In either case, install them above grade by at least 12". At minimum I would go with the air gap type that drains the piping so as to prevent a siphon rather than just check valves.
My back flow preventer on my sprinkler system has to be tested by a certified agent yearly to assure it is working correctly. This year I had to replace a $175 part (basically all the guts of the thing) to keep it from leaking. Mine has a brass frame that allows quick replacement of the working parts of the preventer using just a screwdriver so I saved about $100 by not having to put in a whole new part.

 

[Industrial Toys]

Might be cheaper just to buy your family bottled water! I mean, how much cold water do people actually drink?

 

[ChiefBodie]

you must decide if your families health is worth the expense of a $300 back flow preventer

Learning how to do this the right way the first time is why I posted the topic. Some here seek the least expensive way; that is not my mode.

I appreciate the very good replies and my knowledge of how to get it done right has increased a lot. I noticed the Zurn/Wilkins 375XL has a "blow out port" that says it is useful if used for irrigation systems, or for winterization. I'm looking very hard at putting that model in, along with a screen and drain. Since there is expenditure in money and labor for installation, I only want to do this once so I want it right.

 

[STx]

I was a licensed irrigator for many years, the simple answer is a check valve can't be tested and a backflow prevention valve can. Get the BPV, either an RPZ or a PVB, depending on your elevation changes. PVB needs to be installed 12" above the highest part of your system.

 

[Tractor Seabee]

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.

Been working on my system or I would have responded sooner. There is a type of anti-siphon/vacuum breaker valve used for irrigation. As they are open to atmosphere they must be 12" above grade also. The only approved ones have test connections same as other devices. Testing requirements are the same. The cheap ones are only used as vacuum breakers to allow drainage. A reduced pressure type is the best and most reliable. It is required for facilities where chemicals can be introduced, in medical facilities, and connections to equipment containing water treatment chemicals. Some jurisdictions require them at facility entrance mains to protect their water system and the neighbors. Double check is generally used for irrigation and places like piers. Check valves are not approved. Pecking order of reliability is same as how the prices range.

I always put my circuits in a loop so there is equal pressure at all points all the time. I use the pressure reducer to maintain a constant pressure through fluctuations in delivery pressure and that most design criteria call for 40-50 PSI for irrigation. Main supply pressures can be as high as 100 PSI+ and irrigation parts are not designed for that. A lot of folks use thin wall PVC also to save a few $. My minimum for mains is 1" schedule 40 PVC with 1/2" branches. Never a flow problem. There is more information on the web than you can absorb in a short time. It is a complicated subject and plumbers have to have training and be certified to perform inspections and certifications.

Hope this clarifies. Ron

 

[ChiefBodie]

I have roughly 60psi from the well, using 1" schedule 40 pvc. Where I want to connect that to the irrigation system, I have only 32psi (max) in a 1 1/2 schedule 40 pvc pipe. The well pressure is constant, the irrigation pressure is variable since it is gravity fed.

I will install a reduced pressure backflow preventer to protect the well. I learned that all of these inherently reduce pressure from the supply side to the output side, which is no problem since I am starting with about 60psi. If it reduced that to 50psi I still have far more pressure from the well than from the irrigation lines, but that also introduces a problem.

I would like the irrigation water to be "priority," (when it is available) and use the well water only for backup. When irrigation water is present, it is "free" since it is gravity flow, whereas the well is not. But if I just use a Tee to connect them together, I will be connecting two pipes together where the well has much more psi (always) than the irrigation lines. I presume it would therefore always be running as the "primary" supply which is not what I want.

I'm looking at adding a Zurn 70xl pressure reducer after the backflow preventer. I would use that reducer to reduce the psi from the well supply down to 25 psi, or some other (any) setting below the normal operating pressure of the irrigation system. I'm hoping that when irrigation water is present, with 32psi, it will then automatically be the primary source since it has more pressure than the well psi which I have downgraded. But when the irrigation water degrades, losing psi, once it falls below 25psi the well would kick in. I've never done this before but am presuming that would work?

Final note: Where I want to Tee in and use the well as a backup only runs small demand things like lawn sprinklers or drip irrigation. That stuff runs fine at 32 psi, so I presume/hope it would also run at a little lower psi which I would set the well output to. I have other irrigation "things" that require more psi, but that's not in this location.

 

[Tractor Seabee]

Do you want change over to be automatic or manual? Valves will suffice for manual change. You need put a check valve in the irrigation line to prevent the well pump from back feeding into the irrigation source. You need a fine strainers ahead of all valves in both water source lines clean water to devices. Thy all have small passages that clog easily. To make it automatic; put a solenoid in the well line and a flow sensor in the irrigation source line that operates the solenoid. Tonight I will work on a flow diagram for this, maybe. I would use a double check back flow preventer if mine. Your choice. Keep all your piping clean as you go and flush well before installing heads. Shop your devices. Stay with known brand names and any will give good service. Prices are allover the map as these items have good markups and overheads vary much. I use Amazon a lot. My church gets a doby on all my purchases there. Usually cheaper than the big box stores.

Ron

 

[ChiefBodie]

Very good information, thank you. Yes I would like the switchover from irrigation water to well water (when needed) to be automatic, if possible. That's why I had considered reducing the well output psi to something below the irrigation system psi.

I agree that a check valve is needed to prevent the well from attempting to pressurize the entire irrigation system infrastructure, and only pressurize the single "circuit" that I need. I am looking at adding a flow meter on the 1" well supply so I can monitor just how often the well is supplying irrigation water, and in what volume.

I am homing in on Zurn/Wilkins products as they seem high quality. I have not shopped or researched strainers, and I should do that as the irrigation water sometimes has debris including small bits of frogs in it. :frog: Can you recommend any strainers that would fit on 1" and 1 1/2" pipe?

 

[Tractor Seabee]

Very good information, thank you. Yes I would like the switchover from irrigation water to well water (when needed) to be automatic, if possible. That's why I had considered reducing the well output psi to something below the irrigation system psi.

I agree that a check valve is needed to prevent the well from attempting to pressurize the entire irrigation system infrastructure, and only pressurize the single "circuit" that I need. I am looking at adding a flow meter on the 1" well supply so I can monitor just how often the well is supplying irrigation water, and in what volume.

I am homing in on Zurn/Wilkins products as they seem high quality. I have not shopped or researched strainers, and I should do that as the irrigation water sometimes has debris including small bits of frogs in it. :frog: Can you recommend any strainers that would fit on 1" and 1 1/2" pipe?

Amazon has Zurn products in 1" pipe size. They also have 20 Mesh strainers if you want to sty with Zurn. I used a plastic body made for irrigation strainer/filter. Not very expensive on Amazon, will look for it in the archives and get back. Unless you are using 1 1/2" pipe for the main laterals I think 1" is a large as you need to go, throughout. A 1/2" equalizer line back on for each loop will assure even pressure at all heads in that loop. In reviewing your scenario I do not see you having a big contamination potential. I would be more than comfortable with the double check valve and save the $100+.

In case others are following this thread; those vacuum breaker units have to be the "pressure" type. That's the ones with the test cocks. The others tend to leak under pressure. They also need to be inspected and certified where allowed by the AHJ.

Well, back to my system.

Ron