What on earth is a breeching valve?
A breeching valve, also known as a safety shutoff valve or excess flow valve, monitors pressure and flow in a system. Upon seeing excessive flow, the valve will automatically close, essentially shutting off or “breeching” any flow to the system.
This safety feature works very well when a piping system is used for transporting hazardous materials such as petroleum, gas, or chemicals. It is also effective in pollution control applications. Breeching valves, however, are also finding their way into other systems including fire protection systems in high-rise buildings. At first glance, this may cause some concern since the fire protection community has spent a great deal of time and effort to ensure that control valves are OPEN at all times. NFPA statistics, however, show us that although sprinklers are exceptionally effective, the number one cause of system failure is, and has been for quite some time, due to a shut valve.
taken from NFPA U.S. Experience with Sprinklers report
So what are the benefits of installing a valve that will intentionally close upon excessive flow? Before we answer that question, we need to define excessive flow.
What is considered excessive flow? A sheared riser, leaving an open-ended pipe, is certain to cause excessive flow. A failed fitting on the upper stories of a building might also result in excessive flow. If we wanted to, we could come up with a list of other potentially catastrophic failures, but the real questions we should be asking are, “How often do such failures occur and should we design for them?”
Keep in mind, NFPA standards are minimum standards and such design concepts are usually left up to a risk management approach.
But, let’s just assume that an excess flow valve is going to be installed in a sprinkler system. How would excessive flow be defined? We calculate flow for sprinklers on every project so determining flow is already part of the design process. For example, a light hazard occupancy can be calculated at a density of .1 gpm/ft2 applied over an area of 1500 ft2. If we do the math quickly, we see that.1gpm/ft2 x 1500 ft2 = 150 gpm. If we add 20% for balancing, a conservative figure will result in a total flow of about 180 gpm. So, would we say that anything above this number is considered excessive flow? Of course, this number is based on the traditional concept of “remote area” or can be better identified as the area furthest away or space creating the highest-pressure demand on the water supply. The idea is that if we can supply that area of the system, we can supply any area of the system.
Now, did you notice that I used the words, pressure demand? How would things change if it was flow demand?
Let’s delve into some “what if” cases here. What if the operating area took place immediately adjacent to the riser? What if we calculated the system using an actual “C” value and not the 20 or so year old “C” value required by NFPA 13? For example, new steel pipe has a “C” value of closer to 140, whereas NFPA 13 requires a “C” value of 120 for wet systems. What if we calculated based on a zero cushion or calculated based on what the actual water supply will deliver? NFPA 13 does not require such a calculation but NFPA 16 does for the purpose of determining the reduced duration of foam concentrate. The difference in flows between those two calculations can be significant. What if there are hose racks or a standpipe system involved? No doubt, that could create a significant, variable water demand.
At this point in time, NFPA 13 does not address the issue of excess flow valves. It neither permits nor prohibits the installation of such valves; there is essentially no guidance given on the subject. As revisions are being made to NFPA 13 for the 2022 edition, perhaps it is time to look at the installation and application of these valves? For example, the standard could provide guidance on how much water is too much? Is 50% over the calculated flow the right setting? What should be done about inspection, testing and maintenance? Should breeching valves be prohibited altogether? The correlating committee for NFPA 13 will be looking at these issues in depth during their upcoming meeting in December. In the meantime, if an excess flow valve is specified for a project, the best course of action is to discuss the situation with the project engineer and fire marshal to determine what the proper settings should be and whether the valve is essential in the first place.
As noted previously in this piece, the number one cause of sprinkler system failure is a shut valve. Do we really want to install a valve that will intentionally shut off the water supply to a sprinkler system?”