Reversing the Concern
Testing backflow preventers
NFPA Journal®, January/February 2012
Backflow prevention devices are often used when sprinkler systems are connected to nonpotable public water supplies, especially when the systems are interconnected with alternative sources of water or when antifreeze or other chemicals, such as foam, are used as additives. These devices prevent the reverse flow of water that could contaminate the water supply.
When it comes to periodically testing backflow preventers, NFPA 25, Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, has reversed its concerns over the years. In the first edition in 1992, NFPA 25 called for an annual test to prove the backflow preventer could indeed prevent backflow. In the 2008 edition, a forward flow test was added to ensure that the spring-loaded, one-way check valves incorporated into the devices would fully open when flow is needed. And in the 2011 edition of NFPA 25, the reverse flow test was removed. The standard now requires an annual “forward flow test of the system at the designed flow rate, including hose stream demand, where hydrants or inside hose stations are located downstream of the backflow preventer."
While backflow remains a legitimate health concern, preventing it is now considered outside the scope of NFPA 25. The standard presumes that local or state requirements will continue to ensure that the devices are properly tested by qualified personnel.
Since its 1994 edition, NFPA 13, Installation of Sprinkler Systems, has required that “means be provided downstream of all backflow prevention valves for flow tests at system demand" to facilitate the forward flow test. While NFPA 13 presents this as a performance-type requirement and does not specify the means, the annex has, since the 1996 edition, suggested possible options, such as a test header or other connection downstream of the backflow device or a bypass around the check valve in the fire department connection with a control valve in the normally closed position. Basically, any option that can flow the amount of water needed by the sprinkler system is acceptable.
The NFPA 13 use of the term “system demand" instead of the NFPA 25 term “designed flow rate" has often raised the question of whether there is an intent to verify the design demand pressure as well as the design flow. In other words, whether the NFPA Sprinkler Committee intends the test to determine the adequacy of the system water supply. Some have even proposed that the downstream test valve be throttled until the flow rate equals the system demand, at which point the residual pressure might be compared to that for the original design demand.
As with the 2-inch or “main drain" test, however, checking the system design demand through the forward flow backflow preventer test was never the Sprinkler Committee’s intent. While the pressure drop during the forward flow test might provide information about the condition of the internal check valves, especially when compared with previous test results, the main drain test already serves this purpose. As it prepares the 2013 edition of NFPA 13, the committee has rejected a proposal to record the pressure drop during the forward flow test of the backflow preventer at the time of system acceptance testing, essentially taking the position that the forward flow test is concerned only with sufficient flow, not with pressure.
For the next edition, the committee has proposed an addition to the section dealing with antifreeze systems. The addition would be a reminder about the need for a means of providing a forward flow test for the backflow preventers that are used to isolate antifreeze subsystems. Even smaller backflow preventers must be tested annually to ensure they will flow the downstream water demand when needed.
Russell P. Fleming, P.E., is the executive vice-president of the National Fire Sprinkler Association.