As an engineering student at North Carolina State University, I recall the first time I was ever introduced to the concept of backflow. I believe it was in a fluid dynamics class where I discovered a one-sentence definition in a textbook that said something to the effect of “Backflow occurs when water flows in the reverse direction from its intended path.” That’s it. Years later, while working at Apollo Valves, I took a deeper dive into the backflow world as I began to design backflow prevention products. I sat in utter amazement as I dissected the inner workings of a reduced pressure principle backflow prevention assembly (RP), marveling at its seemingly magical use of hydraulics to prevent backflow. We can all tip our hats to the brilliant engineers at the E.C. Service Company who patented the first RP some 75 years ago. I quickly learned that it is what causes water to flow in the wrong direction that informs how backflow prevention assemblies and devices must be designed, manufactured, installed and maintained.
It is amazing how little the general public knows about backflow, a fact reflected recently when legislators in several states passed misguided laws like ones that limit how often local governments can require testing of backflow preventers, remove the requirement of having only certified cross-connection control technicians test backflow assemblies, and reduce the oversight and enforcement of backflow regulations. The sad fact is that many voting on these changes have no idea what backflow is, or why protecting the public from ingesting contaminated water is an important health consideration.
In the broadest sense, backflow products prevent water from flowing in an unintended direction by employing one or more of the following:
- air gap — a physical separation between the non-potable water plumbing system and the potable water supply
- check valve — a valve that allows flow in only one direction and opens and closes based on pressure differences
- relief valve — a fail-safe, pressure-regulating valve that automatically opens to discharge water when the pressure inside a backflow prevention device becomes unbalanced
The stable of ASSE backflow standards is comprehensive. The first ASSE product standard ever published was in 1964, and it was for a backflow prevention device (ASSE 1001, Atmospheric Type Vacuum Breakers). Since that time, ASSE has published 23 additional backflow standards (see chart above).
As a reminder, here is a little Backflow 101 to help understand the chart:
Hazards are generally considered “high” or “low.” A high hazard is defined as when a contaminant is present in water, meaning something that poses a health risk if introduced into the potable supply. A low hazard is defined as when a pollutant is present in water, meaning something that does not pose a health hazard but might affect the water’s aesthetic quality such as taste, color, or odor. Backflow legend Pete Chapman, who at one time or another worked for just about every major backflow manufacturer in the United States, taught me a simple way to remember the difference between contaminants and pollutants. Contaminant begins with C-O-N, like convict. A convict is a person who did a bad thing, someone who is serving time in prison, so contaminants are associated with high hazards. Pollutant, on the other hand, begins with P-O-L, like politician. Pete said politicians were annoying, but not as bad as a convicts, so pollutants are associated with low hazards. I did not point out to Pete that sometimes politicians and convicts are occasionally one and the same!
Assemblies (like RPs, DCVAs, and PVBs) include test cocks and shutoff valves and are field testable utilizing a backflow prevention assembly test kit. Devices do not include test cocks and are technically not field testable once installed; however some can have their functionality confirmed by exposure to prescribed conditions.
Backflow is caused by two phenomena: backpressure and backsiphonage. Backpressure backflow occurs when an increase in pressure exists on the downstream side of a connection, causing a reversal of flow from its intended direction. Backsiphonage backflow occurs when the supply pressure falls below atmospheric, which can be caused by water main breaks or excessive water demand. When atmospheric pressure becomes greater than the supply pressure, a reversal of flow can take place.
So, there you have it. For over 60 years, ASSE has continued to publish product standards for nearly every conceivable type of backflow preventer. As our population continues to grow, plumbing systems become more complex and water conservation and reuse more common, ASSE will remain at the forefront of promulgating backflow prevention product standards for new applications.
