We all likely have things we believe in, even though we have probably never seen them for ourselves. Depending on where you live, the Northwest United States have Sasquatch, the Alps have the Yeti, Scotland has Nessie — and backflow professionals have the Barometric Loop.
If you are not familiar with this last elusive creature, the 2021 International Plumbing Code (IPC) refers to the barometric loop as a method of preventing backflow caused from backsiphonage. The National Standard Plumbing Code (NSPC) also addresses barometric loops; the Uniform Plumbing Code (UPC®) does not. In my personal plumbing journey — now 50-plus years — I have never seen one, but I honestly do believe they exist.
Section 608.14.4 Barometric loop. Barometric loops shall precede the point of connection and shall extend vertically to a height of 35 feet (10668 mm). A barometric loop shall only be used as an atmospheric-type or pressure-type vacuum breaker.
The theory behind the loop is based on the laws of physics. Atmospheric pressure will not support a column of water greater than a 33.9-foot (10.3 m) water column at sea level. It should be noted that this height decreases with elevation, as atmospheric pressure drops the higher you go above sea level.
This is where we should start to rethink the application of this method. The code above states, “A barometric loop shall only be used as an atmospheric type or pressure-type vacuum breaker.” Backflow education makes clear that there are two degrees of hazard — health and non-health — along with two types of backflow. There are limitations for each method, device or assembly that is utilized. Any vacuum breaker has the minimal limitations of protecting against backsiphonage only. They allow air into the piping system to break a siphon when a loss of pressure occurs. Continuity of water is broken, thus preventing any pollutant (non-health hazard) or contaminant (health hazard) from entering the potable water system.
The barometric loop does not function like a mechanical vacuum breaker because it does not admit air into the piping system. However, it will prevent non-potable items from entering the upstream piping due to a backsiphonage event.
Hypothetically, if the downstream side of the barometric loop is contaminated with a bacterial agent, the bacteria can multiply and migrate though the water. Since a barometric loop does not break continuity of supply between the potable and non-potable source, some substances in the non-potable system could potentially end up in the potable water.
The 2018 IPC Table 608.1, Application of Backflow Preventers, list the barometric loop as suitable for both high- and low-hazard applications for backsiphonage.
Should we, as backflow and code professionals, start reimagining the practical uses or areas we allow these loops to be installed? Have barometric loops reached the limit of usefulness in the backflow industry? If they are only useful on backsiphonage installations, they cannot be used for containment situations. When heat is applied to water, the physical properties of water change. With a temperature increase, water immediately starts to expand in terms of volume and pressure even when heated from 40 degrees Fahrenheit to room temperature. This is thermal expansion, a form of backpressure.
If barometric loops are determined not to be suitable for high-hazard applications, do they really serve any practical purpose? What type of low-hazard isolation situation could benefit from this method?
There are many more effective ways of preventing low-hazard backsiphonage cross-connections. Maybe barometric loops are following the path of the dodo bird — heading for extinction — maybe they will continue to exist in the folklore of backflow stories. Either way, this is a topic that should be revisited.
Hi Matt, I am curious about your “bacterial migration” example of contamination and the argument that it renders barometric loops useless. If this is the case (and I have no evidence that it isn’t) I do not understand how it doesn’t apply as well to any mechanical vacuum breaker installation, unless you’re saying that the check in a PRV would otherwise prevent bacteria from forming and crossing upstream. I do not believe a mechanical check is any more effective other than perhaps delaying migration of bacteria at best in a stagnation or low flow situation. Is there evidence to the contrary? Ie: Does a check effectively act as a barrier for in pipe bacteria growth? Any insight appreciated….
Hello Dave,
Thank you for your interest and comments. This article was written as an opinion and includes my own personal feelings about the short falls of a barometric loop. ASSE and IAPMO remain neutral on the efficacy of a barometric loop.
I have no actual evidence that bacteria can or cannot migrate within a plumbing system that has a barometric loop installed. What I am considering is there is no break in the continuity of water in the system. This may allow bacteria to bloom, grow and migrate through the system.
I agree with you that a check valve in a double check valve assembly or a dual check device can allow bacteria to migrate. In my opinion, if we are looking at a health hazard situation, an air gap or an approved assembly or device, e.g. a reduced pressure principle assembly or vacuum breaker, could offer a more practical and less expensive means of providing high hazard protection.
I also concur that in the event backpressure is somehow applied to a PVB, the check valve does not offer the level of protection needed. This would definitely be a job for the RP.
Thank you,
Matt King