Is 2-Inch Enough for Forward-Flow Testing?

5/26/2022

There has been a lot of discussion on this post regarding forward flow test connections.

NFPA doesn't address sizing of this connection. The project I'm currently working on is strictly sprinkler with Light and Ordinary Group 1 hazards, with no standpipe connections. The maximum expected flow is 250-300 gallons per minute.

The engineer is showing a 2" forward flow test connection piped to an open fitting on an outside wall. I know that fire pump tests are frequently conducted using 1 3/4" nozzles and easily achieve 250 gpm readings.

Does it make sense that a 2" connection would be adequate in this instance?

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15 Comments

Eric R

5/26/2022 07:21:02 am

It is good to note that the most recent edition of NFPA 13 does have a prescriptive requirement of one 2.5" hose valve per 250gpm of system demand. However it also states that alternative means may be provided as long as the assembly can provide the required flow and doesn't require any modifications to the system arrangement to run the test.

Now whether a 2" assembly will be sufficient is directly related to the available pressure of the water supply. Flowing 300gpm through a 2" drain assembly should be pretty easy to achieve if the residual pressure at that rate is 50psi or higher and the drain piping assembly is relatively short.

If alternatively there is only 30psi available at your system demand and your drain needs to run a decent distance to the discharge location then you might be cutting it close.

As a personal recommendation, I always like to provide a NST hose adapter and cap on the exterior wall like this:
https://argco.com/fire-equipment/6510204a.html
Which will allow the inspection company to attach a hose monster nozzle directly to the outlet without needing to setup any fire hose or diffusers (assuming the location is suitable for this arrangement).

Eric R

5/26/2022 07:34:20 am

Oh, and since this is the topic of the day. It drives me nuts that the NFPA 13 annex material for these test assemblies still mentions piping the discharge around the FDC check valve with a bypass as an optional arrangement. There really is no justification for this to still be acceptable.

If the distance from the riser to the exterior is short, which would likely mean there is a low chance of trapping water in the FDC piping, then the cost of a dedicated line would be minimal.

If the distance from the riser to the exterior is long, then running water into the FDC piping could create all sorts of problem with trapped water, corrosion, and discharge from the ball drip assembly.

If the amount of discharge is high (400gpm+) then the clapper assembly in a standard siamese FDC is going to block discharge from one of the outlets and not allow adequate water flow.

matthew mueller

5/26/2022 08:19:05 am

I've only seen a check valve bypass when the FDC is a Storz connection, so no worry of a siamese clapper. Otherwise, I suppose you could removed the siamese to achieve the same thing.

schulman

5/26/2022 08:21:02 am

my state construction office (SCO) requires (2) 2-1/2" hose connections for forward flow testing @ 500 gpm (3 for 750, and 4 for 1000)...etc ...

I stick to my SCO standards as a designer because it covers many if not all scenarios... sometimes more is more ...

Alex

5/26/2022 08:23:41 am

Hi,

To start, Eric, thank you for the in-depth response!

To echo Eric's point, NFPA 13 (2022) 16.14.5.1.1 states that "a 2 1/2 inch hose valve shall be provided downstream of the backflow prevention valve for every 250 gpm of flow rate required by the system demand including hose allowance where applicable"

Now, could you achieve 300 GPM through a 2" pipe... sure. As long as you have the pressure, you definitely can. I would write back and request a 2 1/2" pipe.

Thanks,
Alex

Mark Harris

5/26/2022 08:34:45 am

If any of you are on NFPA 13 committee maybe it makes sense to talk about changing main drain form 2" to 2-1/2" to be both drain and flow connection on a light or ordinary hazard occupancy. Flows greater than 250 would need additional connections as noted above.

Dan Wilder

5/26/2022 09:46:32 am

Anyone can submit a "Public Input" (PI) but plan on a 3-5 year process for it to make it in (I'm not on a 13 committee but on 3 other NFPA's and the E&S for NFSA and we are in discussion for the 2025 editions and beyond). You can also tap into your local/regional AFSA/NFSA reps to have them submit something, but be prepared to provide justification and any testing support you can provide.

https://www.nfpa.org/-/media/Files/Codes-and-standards/Regulations-directory-and-forms/Stds_Dev_Process_Booklet_2018.ashx

Peter

5/26/2022 10:09:53 am

The table for drain size in NFPA 13 states that you can use the size for the drain prescribed based upon riser size "or larger".

Jesse

5/26/2022 08:56:43 am

I'm late to the party again. Eric had an excellent response, and I would echo what Alex said. We typically use a 2.5" valve for every 250-gpm. Yeah, you could get 300-gpm using a 2". I would try to have them authorize the 2.5"

David Kendrick

5/26/2022 10:38:00 am

Has anyone found the original rational for this modification of the standards? That is to require a full forward flow.

I recognize the logic behind the directives but was there any documentable harms or failures that drove this issue?

For quite a while we used the main drain test documentation to validate the systems current performance against the original installation.

A deviation from the original numbers should cause investigation into why.

I cannot recall ever finding a riser check or alarm check "stuck" shut.

Have there been backflow preventer checks (not the relief valve) that "stuck" closed?

Eric R

5/26/2022 11:31:11 am

From a brief archive search on NFPA.org it looks like the requirement to forward flow testing backflows was brought into NFPA 25 in 1998 (I can confirm it is in my 2002 paper edition sitting on my shelf). Below is the link to the Request for Proposals for that edition with the new language starting on page 13.
https://www.nfpa.org/Assets/files/AboutTheCodes/25/ROPF-1997-25.pdf

It is interesting that the substation for the proposal speaks directly towards verifying the static and residual pressures of the flow test at system demand and comparing those results against the hydraulic placard, as opposed to simply exercising the backflow checks to keep them in good working order which is the common reasoning I hear for the requirement in training sessions today.

An interesting nuance can be found between NFPA 25-2020 and NFPA13-2022 where in NFPA13 it states the test assembly is being installed to allow for required testing per 25, but an annex note states that this "flow test" is only interested in measuring gpm flow and not residual pressure. However in NFPA25 the code language calls for performing a "flow test" but is silent on if residual pressure should be recorded during this test. Even checking the proposed changes for the upcoming 2023 edition, I do not see any modifications that speak to whether or not pressure readings should be recorded during this test. There is also not a specific definition of the term "flow test" in chapter 3.

The reasoning I often hear as to why this flow test should not record residual pressure is that sprinkler inspector technicians are not qualified to assess the "adequacy of a water supply to meet a system demand." The defining scope of NFPA 25 is to check for general conditions of system equipment functionality and not to be performing engineering or design tasks so this reasoning is probably valid.

BUT! Just because checking water supply data against the hydraulic demand isn't part of a periodic inspection does not mean it still isn't a good idea to arrange the permanently installed equipment on a brand new system to allow for such an analysis in the future. System modifications, tenant fit-outs, or pipe degradation may someday require a full engineering review of the system to be performed Having a ready made flow test point at the riser will certainly make that job easier!

Dan Wilder

5/26/2022 05:53:55 pm

Nice Eric!

In the conversation had concerning NFPA 13 System Acceptance and NFPA 25 ITM that I have been apart of, the intent (in my opinion) is to install and validate a NFPA 13 compliant system (from original water supply testing through to building turnover).

Afterwards, the owner, through a timely and consistent process of ITM and accompanying ITM activities and paperwork, should be able to identify water supply degradation that "may" indicate issues that need to be verified via an engineering analysis. They aren't saying there is a problem, they are saying it's different and you (Mr. Owner) need to investigate why.

25's Section 1.1 is pretty specific to state (edited for key words) ",,,and the actions to undertake when changes in occupancy,...or water supply that potentially impact the performance of the water-based system are planned or identified." That gets followed up with 4.1.7 and is the owner's responsibility.

Randy Kimbro

5/27/2022 08:06:25 am

As an AHJ, we use the annual forward flow with the pitot measurement to compare the available GPM to the engineered requirement on the hydraulic plate. We want to ensure there is adequate water supply. The static and residual pressures are measured separately using the main inspector test drain. For older systems, we require the installation of one 2.5" hose valve for each 250 GPM.

Although there is language in NFPA 13 and 25 regarding flow "at the base of the riser" we require the 2.5" hose valve to be installed above the riser backflow and above the alarm water flow switch to ensure we are measuring the true GPM that will reach the sprinklers.

Eric R

5/27/2022 09:23:53 am

This brings up another great topic of discussion.

"Base of the Riser" does not seem to have a specific NFPA definition. The closest I found was system riser in NFPA 13.

"3.3.225 System Riser.
The aboveground horizontal or vertical pipe between the water supply and the mains (cross or feed) that contains a control valve (either directly or within its supply pipe), a pressure gauge, a drain, and a waterflow alarm device."

A very common problem we have when preparing drawings for existing system modifications is hydraulic placards that have the wrong values document in the "system design" section for required water flow and residual pressure. NFPA 13 calls for those values be recorded for the "base of riser" per:

"29.4.3
The sign shall include the following information:
(4) Required flow and residual pressure demand at the base of the riser or fire pump where applicable"

but upon review of actual system drawings and calculation sheets we will find that the values documented are actually for the "source" node of the design. I have learned that if the hydraulic placard's water flow demand value seems to include the outside hose extra amount, then it's likely that the residual pressure number is based on the requirement way out in the street and not at the "base of the riser".

My opinion is that the base of riser point is below(before) the "system riser" equipment (control valve, check valve, flow switch, and main drain), but after the backflow preventer assembly. This works especially well if you have a manifold riser assembly with multiple system risers supplied from a single water supply. It would also insure that the residual pressure value on the placard doesn't include the loss for the BFP which if included could create unnecessary concern when a main drain test results in a residual pressure lower than the value on the placard.

With this in mind, installing the BFP flow test point directly after the backflow is best as it will be able to perform it's stated NFPA 25 purpose, but also allow for validation testing of the system's hydraulic placard as part of a design review.

Now I just need to figure out a way to make sure new systems not installed by my team get the proper data put on them! Just last month we went to do a tenant fit-out at a brand new mixed use building that had be CO'd only two months prior. Six shiny hydraulic placards had just been hung, and every last one was completely wrong!

Randy Kimbro

5/31/2022 10:42:33 am

ERIC R - I agree with the misinformation on some hydraulic placards. I have seen wrong street addresses, missing data, and inaccurate flow rates. As an AHJ we also really dislike the newer trend of using stickers instead of permanent metal plates for the hydraulic information. The stickers sometimes fall off the riser, are really not considered permanent, and can actually get painted over when they are placed on an adjacent wall instead of on the riser as required.

Is 2-Inch Enough for Forward-Flow Testing?

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