A Marriage Made in a Stairwell
As seen in FPC Magazine, January 2012

Like many in our industry, when I walk into a building I tend to look for and notice things differently than the usual visitor. I look for a sprinkler system. While some may choose to take the stairs for exercise, I do it to check out the building's riser; it has just become a habit. What I am always most interested in is that collection of pipe, valves, fittings, and components that make up the Floor Control Assembly.

A quick review of the past and current editions of NFPA 13, the Standard for the Installation of Sprinkler Systems, provides an unchanging drawing of a typical Floor Control Assembly, but what I usually find on my "stairwell tours" rarely resembles that drawing. What I do find during my tours, on most systems less than a couple of decades old, are one piece test and drain valves being used instead of the "inspectors test loop" as shown in the standard's drawings. What these valves do is remove no less than 16 individual pieces and an equal number of connections from an already crowded area. Designed to meet the requirement of providing an inspector with an easily accessed test valve, along with a sectional drain valve, they also provide the installing contractor with a simple, reliable, time- and space-saving alternative to the as-drawn "inspectors test loop".

As municipalities start to adopt the 2010 Edition of NFPA 13, I am likely to start seeing some different scenery on my tours; more pressure relief valves. In the 2007 and earlier editions of NFPA 13, wet systems required Pressure Relief Valves to be installed for two specific applications: gridded systems and downstream of Pressure Reducing Valves. In the 2010 Edition of NFPA 13, there was a change made to 7.1.2, which now states that a wet pipe system shall be provided with a relief valve not less than ½" in size;, requiring relief valves downstream of Pressure Reducing Valves carried over unchanged. While NFPA 13 makes no specific requirements as to where Relief Valves be located, other than downstream of the Pressure Reducing Valves, a number of manufacturers, including Victaulic, Guardian, and AGF Manufacturing, have made provisions for their inclusion on Floor Control Assemblies and/or test and drain valves.

One of the cleanest examples of this marriage of test and drain valves and pressure relief valves can be found on the AGF Model 1011 TESTanDRAIN series. The valve is made in the U.S.A., is available in five sizes with seven different orifice options, and the angled patterned body and multiple port ball creates the unique situation that allows for the installation of the relief valve, after doing a system integrity test, without having to drain down the system, a big time- and water-saver. Additionally, there is a tapping on the underside of the valve body immediately downstream of the ball to accommodate the drain piping coming from the Pressure Relief Valves. This layout provides a quick, straightforward solution to NFPA 13, A., which states that consideration should be given to piping the discharge from the (relief) valve to a drain or other safe location.

All of the different manufacturers' valves can be purchased individually; additionally, some are used as the OEM test and drain valve on preassembled riser manifolds or floor control assemblies offered by multiple manufacturers.

Pressure Relief Valves are the other half of this convenience couple. While the test and drain valves sit in the stairwells, waiting to perform their intended purpose, it is the Pressure Relief Valves that monitors the day-to-day fluctuations of system pressure build up. The change in the 2010 NFPA 13 to require all wet systems to include Pressure Relief Valves was the result of the increased concerns of MIC that led to the desire to remove as much air from the system as possible, but, in so doing, left the system vulnerable to increased pressure created by thermal expansion.

As stated above, NFPA 13 directs us as to when and where Pressure Relief Valves are required; it is, however, FM 1359, Approval Standard for Trim Water Pressure Relief Valves and UL 1478A, Pressure Relief Valves for Sprinkler Systems, that determine the performance requirements and operational characteristics of those valves. Pressure Relief Valves (PRV's) are placed into systems to protect them from catastrophic damage caused by an internal pressure buildup above their "rated" capacity. Therefore, according to both Standards, factory-set PRV's are identified with a "rating" number that relates to the pressure limits of the system they are being installed to protect and is not the specific pressure at which the PRV will start to relieve.

Consider a hypothetical system built with components rated for 175 PSI service limit; since it is the job of the PRV to protect the system the valve should be designed to open and start to relieve pressure before the pressure in the system builds to 175 PSI and then bleed off enough pressure to keep the system safe. While the wording in the two standards is different, the basic requirements are that a PRV open at a point between 90% and 95% of its "rated" pressures and then reseat, or close, before reaching 80% to 85% of its "rated" pressure. So, if one considers again our hypothetical system built with 175 PSI "rated" components including a Pressure Relief Valve "rated" at 175 PSI, that PRV, if it is performing according to the applicable FM/UL standards, should start to relieve pressure in the system as soon as the pressure approaches 158 PSI to 166 PSI, and it should allow the pressure to bleed off the system until it drops into the 140 PSI to 148 PSI range.

Putting our hypothetical system aside, we all know that in the real world many systems are designed with static pressures above 175 PSI, so a PRV designed to open and close below that pressure point will cause problems in the system. NFPA 13 makes provisions for those systems in 7.2.1 by saying that the PRV shall operate at 175 PSI or 10 PSI in excess of the maximum system pressure, whichever is greater.

So, when it comes to choosing a test and drain valve and a pressure relief valve, like with any marriage, picking the right partner is important. Consider using the test and drain valve that best meets your needs from the standpoint of layout, features, and benefits and mate it with the pressure relief valve designed to accommodate that static pressures the system will be operating under.

By: George McHugh

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