Napa / St. Helena / American Canyon   |  
1370 Trancas St #331  •   Napa, CA 94558   •   (707)-224-7497     |  
Tester License  #14456     |  

Backflow Explained            

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!

Types of Backflow Preventers            

There are five distinct types of piping or mechanical assemblies which are considered to be backflow prevention assemblies; but, it must be stressed that these are not allequally acceptable as protection against all types of hazards. The degree of hazard must be assessed along with they 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. Its 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 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.


The DCDA is composed of a line-sized double check valve assembly with a specific bypass meter and meter-sized double check valve assembly. The meter registers accurately for very low flow rates to detect any unauthorized use of water. This assembly is used when the protection of a double check valve assembly is required, yet where the added requirement of detecting any leakage or unauthorized use of water exists. Normally these assemblies are reserved for use on fire sprinkler lines.

Copyright © 2013 Napa Valley Backflow, LLC.     •     All Rights Reserved.
1370 Trancas St   #331     •     Napa, CA 94558     •     (707)-224-7497