Backflow FAQ

Anytime you use water for industrial purposes, you are in need of a backflow prevention valve. Imagine, for example, that you own a car wash. One day, the water pressure supplied to your property may drop unexpectedly. When this happens, the water flow to the soap water tank could reverse. When water pressure is restored, the local city water can be contaminated by the soapy water from the tank. Every building on your street could then have soapy water flowing out of their taps. Obviously, in industry, things could get even more extreme. Facilities that process acids, toxic chemicals, or sewage need to prevent a reversal of water flow at any cost.

This is where a backflow valve comes in. During a time of water pressure fluctuation, the valve will prevent your facility's materials from flowing into the water supply.

If you need a backflow device (valve), you will usually be notified by the city or county's water or health department. Most commercial businesses will need backflow devices installed, particularly when they are located in hilly areas or areas with volatile water pressure conditions.

The building owner can install the device himself or herself as long as all laws and regulations are followed. Or, the owner can hire a licensed backflow certifier.

The cost of a backflow device will vary according to size, which varies from 3/4 inch (homes) to 10 inches (for large facilities) and difficulty of installation. In most cases, backflow devices must be tested and certified annually or more often, as determined by your city, county, or state's regulation. Most valves can be tested in an hour or less.

After completion of test, the owner of the backflow device is given a certified test report. Most devices pass inspection. But if the device fails, there is a legally enforced time limit in which the valve must be repaired or replaced.

We are licensed and certified in all areas of backflow installation, certification, and maintenance. We hope that you will contact us. However, whether we get your business or not, we strongly recommend that whoever does handle your backflow installation is certified and licensed. This is essential for the continued protection of our most important resource - water!

From Title 17 of the California Code of Regulations ("CCR Title 17"):

13.14.130 Inspection and testing of backflow prevention assemblies.

A. The director shall have a certified inspection and operational test performed after installation of the approved backflow prevention assembly. Each backflow prevention assembly installed on the premises of a customer shall be inspected and tested at least once per year. In those instances where the director deems the hazard to be great enough, the director may require inspection and testing at a more frequent interval.

B. The inspection and testing shall be at the customer's expense and shall be in the amount established by city council resolution. Fees paid to the city for this service shall not exceed the reasonable cost for providing the inspection and testing service. Inspection and testing shall be performed by certified personnel of the city's public works department.

C. The purchase, installation, maintenance and/or replacement of an approved backflow prevention assembly shall be the sole responsibility of the customer.

D. The customer shall be notified in advance of the date when the test(s) are to be performed so that the customer or the customer's representative may be present during the inspection and testing. Any backflow prevention assembly found to be defective shall be repaired or replaced at the customer's expense.

E. Records of installation, tests, repairs and overhauls shall be kept by the public works department and be available for five years for review and audit by the health agency. [Ord. 08-1308 § 3, 2008; Ord. 1094 § 1, 1995.]

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There are six common types of piping or mechanical assemblies which are considered to be backflow prevention assemblies; but, it must be stressed that these are not all equally acceptable as protection against all types of hazards. The degree of hazard must be assessed along with the type of cross-connection present to determine which type of backflow prevention assembly is most suitable to the situation.


An Air Gap is a physical separation of the supply pipe by at least two pipe diameters (never less than one inch) vertically above the overflow rim of the receiving vessel. In this case line pressure is lost. Therefore, a booster pump is usually needed downstream, unless the flow of the water by gravity is sufficient for the water use. With an air gap there is no direct connection between the supply main and the equipment. An air gap may be used to protect against a contaminant or a pollutant, and will protect against both backsiphonage and backpressure. An air gap is the only acceptable means of protecting against lethal hazards.


The AVB is always placed downstream from all shut-off valves. The air inlet valve closes when the water flows in the normal direction. But, as water ceases to flow the air inlet valve opens, thus interrupting the possible backsiphonage effect. If piping or a hose is attached to this assembly and run to a point of higher elevation, the backpressure will keep the air inlet valve closed because of the pressure created by the elevation of water. Hence, it would not provide the intended protection. Therefore, this type of assembly must always be installed at least six (6) inches above all down stream piping and outlets. Additionally, this assembly may not have shut-off valves or obstructions downstream. A shut-off valve would keep the assembly under pressure and allow the air inlet valve (or float check) to seal against the air inlet port, thus causing the assembly to act as an elbow, not a backflow preventer. The AVB may not be under continuous pressure for this same reason. An AVB must not be used for more than twelve (12) out of any twenty-four (24) hour period. It may be used to protect against either a pollutant or a contaminant, but may only be used to protect against a backsiphonage condition.


The PVB includes a check valve which is designed to close with the aid of a spring when flow stops. It also has an air inlet valve which is designed to open when the internal pressure is one psi above atmospheric pressure so that no non-potable liquid may be siphoned back into the potable water system. Being spring loaded it does not rely upon gravity as does the atmospheric vacuum breaker. This assembly includes resilient seated shut-off valves and test cocks. The PVB must be installed at least twelve (12) inches above all downstream piping and outlets. The PVB may be used to protect against a pollutant or contaminant, however, it may only be used to protect against backsiphonage. It is not acceptable protection against backpressure.


The Double Check Valve Assembly consists of two internally loaded, independently operating check valves together with tightly closing resilient seated shut-off valves upstream and downstream of the check valves. Additionally, there are resilient seated test cocks for testing of the assembly. The DC may be used to protect against a pollutant only. However, this assembly is suitable for protection against either backsiphonage or backpressure. This type of device is typically in use at residential properties in the city of Napa.


This assembly consists of two internally loaded independently operating check valves and a mechanically independent, hydraulically dependent relief valve located between the check valves. This relief valve is designed to maintain a zone of reduced pressure between the two check valves at all times. The RP also contains tightly closing, resilient seated shut-off valves upstream and downstream of the check valves along with resilient seated test cocks. This assembly is used for the protection of the potable water supply from either pollutants or contaminants and may be used to protect against either backsiphonage or backpressure. This type of device is typically in use at residential properties in the city of Saint Helena. It also used for irrigation lines and commercial properties in Napa, Saint Helena and American Canyon.


This assembly type consists of either two internally loaded independently operating check valves and a mechanically independent, hydraulically dependent relief valve located between the check valves (RPDA), or just two internally loaded check valves (DCDA). These devices are installed as bypass devices with a meter on fire service connections. They detect leaks and unauthorized use. If you have a dedicated fire service line and backflow, you will, virtually in all cases, have a detector assembly installed on your fire device.