Thread: Irrigation System

Can a double check valve be used instead of a vacuum breaker in a lawn sprinkler/irrigation system?

Thanks

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Yes, that is the standard here. I never see a vacuum breaker, only double check valves. Most municipalites require a double check valve on the main feed within a few feet of the meter. But then all of our meters are underground a the street since we don't have many basements.

No. A double check valve is not an approved backflow preventer under any code I have read. How do you tell it has failed or a backflow/back pressure situation exists?

2003 IRC P2902.4.3 Lawn Irrigation systems. The potable water supply to lawn irrigation systems shall be protected against backflow by an atmospheric-type vacuum breaker, a pressure-type vacuum breaker or a reduced pressure principle backflow preventer...
Section 2902.2 Backflow protection. specifies the types allowed and standards in table 2902.2

There is a provision with state guidelines that can require periodic testing, but as far as I have seen, the state leaves it up to the local water provider or municipality to enforce testing of the valve, and none have required it yet.
Jim

This is from one of the local municipalities, describing their requirement for double check valves.

http://www.cityofkeller.com/CD/PDF/S...ionHandout.pdf

This is a description from Watts
http://www.watts.com/pdf/1915345.pdf

This is from the Texas State administrative code
See method number 3
SUBCHAPTER DSTANDARDS FOR LANDSCAPE IRRIGATIONRULE §344.73Backflow Prevention Methods

All irrigation systems connected to a public or private potable water supply must be properly connected through one of the following backflow prevention methods:
(1) Atmospheric vacuum breakers. Atmospheric vacuum breakers are designed to prevent only back siphonage. Therefore, atmospheric vacuum breakers must not be used in any irrigation systems where back-pressure may occur. There cannot be any shutoff valves downstream from an atmospheric vacuum breaker. Where atmospheric vacuum breakers may be used, they must be installed at least six inches above any downstream piping and the highest downstream opening. Where local topography effectively prohibits such installation, the executive director shall be consulted for alternative acceptable installation criteria. Such alternative criteria must provide equivalent protection to the potable water supply. In addition, continuous pressure on the supply side of an atmospheric vacuum breaker is prohibited. Where atmospheric vacuum breakers are used in an irrigation system, a separate atmospheric vacuum breaker must be installed on the discharge side of each water control valve, between the valve and all of the sprinkler heads which the valve controls.

(2) Pressure-type vacuum breakers. Pressure-type vacuum breakers are designed to prevent back siphonage and can operate under continuous pressure. Pressure vacuum breakers must be installed at least 12 inches above any downstream piping and the highest downstream opening. Where local topography effectively prohibits such installation, the executive director shall be consulted for alternative acceptable installation criteria. Such alternative criteria must provide equivalent protection to the potable water supply.

(3) Double check valve assembly backflow preventors. Double check valve assembly backflow preventors are designed to prevent back pressure and back siphonage of water not containing any toxic substance. They may be used where water supply pressure and back pressure on the backflow prevention device may continuously exist. If a double check valve assembly is installed below grade, there must remain adequate space for testing and repair of the device. Test cock plugs must be of non-ferrous material. Test cocks shall not be used as supply connections and must be plugged except when being tested.

(4) Reduced pressure principle backflow prevention assemblies. Reduced pressure principle assemblies are designed for water containing toxic or non-toxic substances and for back pressure and back siphonage. They must be installed 12 inches above grade in a location so as to insure that the device will not be submerged. In addition, adequate provisions must be made for any water which may be discharged through the assembly relief valve.

(5) Air Gap. An air gap, when used must be installed and maintained in accordance with the standards established in the American Waterworks Association M14 Manual on Cross Connection Control.

Hands down, no contest -- you are correct. Keller and countless others allow a double check valve.

"(3) Double check valve assembly backflow preventors. Double check valve assembly backflow preventors are designed to prevent back pressure and back siphonage of water not containing any toxic substance. "

Does anyone in Keller or Texas use fertilizer, ant poison or any chemical on their lawn?

From City of Corpus Christi.

Yes, I will agree there is a risk with back siphonage and there may be better protection available, but then I don't make the rules, I just play by them.
Jim