How Much to Flow in Forward-Flow Test?

3/20/2024

When doing a Forward Flow on a Sprinkler System what is the Minimum # that Fire Marshals are looking for?

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10 Comments

Pete H

3/20/2024 06:40:18 am

From NFPA 13 (2016 edition):
8.17.4.5.1 Backflow Prevention Valves. Means shall be provided downstream of all backflow prevention valves for forward flow tests at a minimum flow rate of the system demand including hose allowance where applicable.

A.8.17.4.5.1 System demand refers to flow rate and pressure. This test is only concerned with testing at the proper flow rate.

The full flow test of the backflow prevention valve can be performed with a test header or other connection downstream of the valve. A bypass around the check valve in the fire department connector line with a control valve in the normally closed position can be an acceptable arrangement. When flow to a visible drain cannot be accomplished, closed loop flow can be acceptable if a flowmeter or site glass is incorporated into the system to ensure flow. When a backflow prevention device is retroactively installed on a pipe schedule system, the revised hydraulic calculation still follows the pipe schedule method of 11.2.2 with the inclusion of friction loss for the device.

Bruce Seiler

3/20/2024 09:18:57 am

The minimum flow rate should be the highest demand for the sprinkler system including any inside hose allowance. Outside hose allowance does not need to be considered for the forward flow test since it wouldn't be required to flow through the backflow. So, if you had a light hazard occupancy with calculations with design criteria of 0.10/1500, your demand would be (minimum) 250 gpm including the 100 gpm outside hose. You would be required to flow a minimum 150 gpm for the forward flow test. One thing to note, NFPA does not require the residual pressure be documented, however we document this number to ensure the actual system demand is being met. We had two cases where the flow rate was met, but the residual pressure was a lot lower than anticipated due to a valve that was not fully open. This problem could also be shown during a 2-inch drain test, but not always due to a lower flow rate. Again, not a requirement, but another good way to ensure the water supply is as expected.

Jack G

3/20/2024 10:11:34 am

Off the top of my head :
A annual flow test of the backflow preventer is not an nfpa 25 requirement. 9.6.2.1 in 13 specifies the test.
However a forward flow test ( just system demand flow and hose streams) is a requirement. ( not necessary to record pressure to meet requirement ) . Recording the pressures - to check for problems , however , is a great idea.

Jeff

3/20/2024 10:31:52 am

2020 NFPA 25 - 13.7.2.1

All backflow preventers installed in fire protection system piping shall be exercised annually by conducting a forward flow test at a minimum flow rate of the system demand.

Brandon

3/20/2024 03:08:20 pm

NFPA 25 2017 edition.
13.7.2.3 Where connections do not permit verification of the
forward flow test at the minimum flow rate of system demand,
tests shall be conducted at the maximum flow rate possible.

Can someone explain this code?

Glenn Berger

3/20/2024 10:44:56 am

The purpose of the forward flow test is to measure the pressure loss in the system of the backflow prevention assembly. The minimum flow rate required is the calculated sprinkler flow for the system(s) being protected.

Randy Kimbro

3/20/2024 11:29:59 am

Hi Glenn, as an AHJ I respectfully disagree. The forward flow is not to measure pressure loss. It is designed for two criteria. First, to exercise the backflow preventor to ensure it opens fully. And second to measure the riser flow rate (pitot reading) to ensure it meets or exceeds the required GPM as documented on the riser hydraulic tag. Those annual tests are extremely valuable for the fire department to have confidence that the sprinkler system will discharge water as designed in case of a fire.

Dan Wilder

3/20/2024 11:50:55 am

It's to exercise the valve components to the working flow conditions expected. There is no requirement to record pressures for this specific activity within NFPA 25. Good practice to record a residual pressure, sure, as it provides good data year to year for possible water supply investigation substantiation.

Dan Wilder

3/20/2024 11:59:24 am

Specifically for 25, just meeting the flow rate as noted by others.

As an install per 13, that has changed within the 2019 and further within the 2022 version, now requiring a 2½" hose valve per 250 GPM of system demand, or other approved means, to perform that forward flow without system modification. Testing through the FDC is problematic as the clapper will close one side of the valve leaving only the single 2½" outlet.

That could mean just hose valves within the riser room, a test header or roof manifold setup, or use of downstream hose valves....and gets involved on larger, high volume systems.

https://www.meyerfire.com/blog/solutions-for-the-overlooked-forward-flow-test

Jesse

3/20/2024 01:27:35 pm

Lotta good answers here but I want to reiterate what Dan said. The difference between 2016 and earlier versions of NFPA 13 will look different than those governed by 2019 and 2022

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How Much to Flow in Forward-Flow Test?

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