How to Test, Verify Dry System Meets Demand?

10/29/2025

Forward flow testing for dry systems As an AHJ, this seems like a simple question, but I cannot find an answer.

We are diligent in enforcing the annual forward flow for wet systems. So, how do we verify the available water supply meets the hydraulic GPM requirements for dry systems?

The annual dry trip test tells us only that water is available and the backflow device opens. We do have one occupancy that placed a shutoff valve ("slam valve") near the top of the riser. They close that valve for the annual test and trip the system, only allowing water in that small section of pipe where they also installed hose valves for the flow test with pitot readings. The valve is chained open normally.

How do others measure GPM annually on dry systems to ensure it meets the designed system demand?

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6 Comments

Dan Wilder link

10/29/2025 08:05:51 am

NFPA 25 Section 13.7 (26 ed.) states that the system flow rate needs to be achieved. You're not testing the water supply, per se, you're verifying that the valve will open at the system demand. If the water supply needs to be verified, that should be with a flow test per NFPA 291 or other modeling efforts.

Ideally, there is some valve setup that allows the testing (bypass at the FDC, hose valves, tee-valve into a Storz connection) to allow the test orifices to be attached to a hose monster or smooth bore orifice to get readings from. We have had to retrofit hose valves onto many risers to perform forward flow testing.

You should not have to test through the dry valve, just a point downstream of the backflow and prior to the dry system valve.

We do have a couple properties that allowed a tee above the dry valve and below an upper control valve that has a normally closed butterfly valve leading to a test header to accommodate both a forward flow test of the back flow but to also satisfy that the valve will also operate correctly at the system flow rate and required pressures. This is well above most of our other properties and definitely not the norm.

Randy Kimbro

10/29/2025 08:55:06 am

Dan, you hit on our issue directly with NFPA 25 Section 13.7.

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.

When verifying that the valve will open at the system demand, the only way to do so is measuring flow with a pitot to ensure we are reaching system demand. We are stuck on how to do that annually for dry systems.

We have a couple systems with a monitored tee above the backflow which enables that testing. Are there other options for dry systems?

I respectfully disagree with using NFPA 291. That is for fire flow testing for hydrants, not risers.

Dan Wilder link

10/29/2025 09:28:28 am

The reference to 291 was for verification of water supply which is different than a forward flow test to verify the backflow works as intended. If I read the original post incorrectly, it was not my intent to mix the two.

There are no requirements to flow the system demand through any other valve other than the backflow, and nothing that prevents it either. The original installation "should" have provided means to test without major modifications to the system, if not, that needs to be changed. Beyond that, there is no other normal procedure we perform to comply with the forward flow test requirements regardless of systems downstream of the backflow.

Our primary is hose valves/Storz to smooth orifices & Pitot or Hose Monsters
Rarely a flow meter if installed.

Anthony

10/29/2025 08:20:41 am

Forward flow testing is to ensure the backflow preventer is working properly supplying the riser not making sure the riser is fictional. The trip test on the riser ensures then dry valve is fictional. When you add those two together as Dan says you should have a working system.

Jesse

10/29/2025 09:16:29 am

I think there are several issues here. First, the forward flow test is to ensure the BFP is functional, so not every system downstream of the BFP will have hose connections.

The trip test is to ensure the dry valve is operational.

I think if the concern is whether the water supply is able to support the dry system still, Dan's recommendation of conducting a hydrant flow test and then comparing the results to the original install flow test is the best bet.

Jonathan Joseph

10/29/2025 09:19:32 am

If they installed hose valves on the riser as mentioned, you should be able to achieve testing your backflow and system demand. For example if your system demand is 400gpm at the base of the riser and there are (2) 2 1/2 hose valves you should be able to meet the requirements. Very common nowadays to install mechanical tees with hose valves on risers. Or use a bypass around the FDC check valve and test header valve normally closed.
And also, where the water is going flow into is important in certain jurisdictions.

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How to Test, Verify Dry System Meets Demand?

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