Backflow preventers are included in fire sprinkler systems to protect public health from contamination by preventing water flow back into the public water grid. In an opposite manner, the forward-flow test for backflow preventers was created to ensure the sprinkler system can be served by enough water in a fire condition.
Backflow preventers (double check or reduced pressure zone) type have potential to fail closed where not exercised over long periods of time. Reduced pressure zone backflow preventers are particularly susceptible with the potential for development of closed memory in their spring mechanisms.
Reduced Pressure Zone type backflow preventers are especially important to exercise spring mechanisms to ensure full forward flow will be available in a fire condition (Ames/Watts 4000SS Model Shown)
The Test Requirement
NFPA 25 (2002 Edition Section 18.104.22.168, 2008-2014 Section 22.214.171.124, 2017 Section 126.96.36.199) requires annual testing of the backflow preventer at the designated system flow rate, including hose demand, where hydrants or inside hose stations are located downstream of the backflow preventer. Where a means is not provided at maximum demand, test shall be conducted at the maximum flow rate possible (NFPA 25 20002 Edition Section 188.8.131.52.1, 2008-2011 Section 184.108.40.206, 2014 Section 13.6.3, 2017 Section 220.127.116.11).
Section of interior of Double Check Backflow Preventer (single tube style shown from Ames/Watts 757 Model)
The Design Requirement
While testing can be conducted at the maximum attainable flow the system will allow, the system must be designed with a means of conducting this test. In my experience this is one of the most often overlooked requirements within fire sprinkler system design.
NFPA 13 now requires a way to test the forward flow downstream of all backflow prevention valves at a minimum flow rate of the system demand including hose allowances (2013 Section 18.104.22.168.1, 2016 Section 22.214.171.124.1). Editions of NFPA 13 before 2013 simply stated that the backflow prevention assembly shall be forward flow tested (2002 Section 126.96.36.199, 2007-2011 Section 10.10.2.5.1).
Design Solutions to Accomplish the Forward Flow Test
Option 1: Use the Annual Pump Test and Header (When a Fire Pump is Present)
Perhaps the easiest option to conduct this test is to use a fire pump's test header to flow water out of the building. If the backflow preventer is installed on the service/suction side of the fire pump, then a separate forward flow test is not even required as the annual fire pump test already causes the backflow to be tested (NFPA 25 2002 Section 188.8.131.52.4, 2008-2011 Section 184.108.40.206.4, 2014 Section 220.127.116.11.2, 2017 Section 18.104.22.168.2). However, if the backflow is on the system/discharge side of the fire pump, then running a feed with a normally-closed valve to the fire pump test header allows the test header to serve both the annual fire pump test or the forward-flow backflow test.
Option 2: Bypass the Fire Department Check Valve
NFPA 13 (2016 A.22.214.171.124.1) poses one option to achieve a means for this test with the use of a bypass around the check valve serving the fire department connection. This bypass would need to include a supervised indicating valve that is normally in the closed position.
Option 2: Provide a bypass around the check valve serving the fire sprinkler system with a supervised, normally-closed valve to enable forward flow tests out the fire department connection.
Providing a bypass around the check valve enables flow to be run out the fire department connection. This works well to take water outside the building and can be directed with testing hoses, however, care should be taken to address clappers inside the fire department connection when they are provided. Some clappers may be removed and replaced in the field to allow a full flow, while others may be directed to allow flow through one side of the fire department connection. Depending upon the system design, this may be a fairly easy method to meet the requirement.
Option 3: Provide Hose Connections for Testing
If a riser has exterior access, another method of allowing testing of the backflow would be to provided hose valves on the riser itself. Hose connections could be made onto the valves and run to the exterior of the building for the test. Typically, each 2-1/2 outlet should be able to provide 250 gallons per minute of flow. Small low-hazard systems might only require two hose connections to enable this method.
Option 3: Provide hose connections on the system riser itself allows hoses to be attached and run out of the building.
Option 4: Size the Main Drain to Handle the Forward Backflow Test
NFPA 13 suggests that upsizing the main drain would provide a means to conduct the backflow test (2016 Section A.126.96.36.199.2). Depending upon the hazard of the system, this may result in a significantly larger opening in the exterior wall for drainage and for most systems would certainly be larger than a typically large 2-inch main drain. I can't imagine many architects like the look of a large downspout nozzle on the building, but it could be much more sightly than several of the other options listed.
Option 5: Install a Designated Backflow Test Header
One clear option that is always available is using a designated test header specifically for the forward flow test. Just like a fire pump test header, this would result in a through-penetration to the exterior where water can be clearly directed. Signage is important for any exterior testing equipment to clearly differentiate itself from fire department connections.
Option 5: Perhaps the cleanest option, run a dedicated test header to the exterior of the building for the backflow preventer achieves the intent of the forward backflow test
Option 6: Use Standpipe Hose Connections (where provided)
Lastly, where standpipe hose connections are already available in the building, these outlets could provide enough flow to test the backflow preventer. This test could be the most difficult to achieve, however, as doing so would require a coordinated effort with multiple hoses in different locations to flow outside the building.
Option 6: Using standpipe hose connections is a built-in way to run the forward flow test for backflow preventers, but requires multiple hoses and a coordinated effort for testing
The forward flow test for backflow preventers is one of the most commonly overlooked requirement for fire sprinkler systems which could impact the actual performance of fire sprinkler systems. Solutions, while cost impacting, exist and are readily achievable to meet the requirement.
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NFPA 13: Standard for the Installation of Sprinkler System, 2013. National Fire Protection Association, 2002-2016 Editions.
NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection, 2002-2017. National Fire Protection Association, 2002-2017 Editions.
Trieber, Bob. “Forward Flow Testing of Backflow Devices.” SQ, no. 4, ser. 2010, July 2010, pp. 11–12. 2010, doi:01/10/18.
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Joseph Meyer, PE, owns/operates his own Fire Protection Engineering practice in St. Louis, Missouri. See bio on About page.