What is a Flow Test?

MeyerFire University | FX106.10

By Franck Orset

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• Notes Page

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TRANSCRIPT

WHAT IS A FLOW TEST?

OVERVIEW

A flow test, or more formally known as a fire hydrant flow test, is a test method that involves flowing water out of fire hydrants in order to understand how a water supply performs hydraulically. 

The test is intended to reveal two things about the strength of a water supply – its available pressure and its available flow.  

As the amount of water flowing out of a system increases, the available pressure typically decreases. By measuring a few points on the water supply, we can develop a relationship and begin to understand the strength of a water supply along various points of that water supply.  

A flow test consists of checking the static pressure of the system, pressure obtained with no flow condition, and the residual pressure for a given flow. 

This test is generally done by using at least 2 hydrants, one for the pressure and one for the flow, and the results can be used for different purposes. 

GOAL #1: MEET HYDRAULIC DEMANDS

The first purpose of a flow test is to determine whether the water supply is sufficient to meet all the hydraulic demand point of the sprinkler systems, plus the additional need for manual firefighting. 

That’s enough water for all of the appropriate sprinklers to flow and suppress a fire, at their required pressure, AND to also allow some water for facility personnel or the fire department to also flow water onto the fire.  

We call the needed amount of water the demand of a system, and the water supply the available supply for a system. The design of a system needs to make sure that the demand is less than the available supply. Otherwise, a fire could overcome the system and manual firefighting efforts and the structure and lives could be compromised.

GOAL #2: CHECK FOR DEVIATIONS OVER TIME

The second purpose of a flow test is to check possible deviations over time. The results may be better, if additional pumps or elevated tanks are provided, or if the underground mains have been improved with larger section of pipes or provision of additional loops. 

But they can also deteriorate, possibly because of other users on the same water supply that may take water for their own needs. 

VARIATION

It is not rare to have large variations of water availabilities on a system depending on the time of the day, or depending on the season. This kind of variation is expected.  

Flow tests are only a “point-in-time” sample of how a water supply behaves. It’s a snapshot in time. We’re not recording how the supply reacts hourly, daily, or seasonally.  We measure a single point in time, then adjust by a safety factor that we have to deem is appropriate to adjust for this uncertainty. 

We’ll explore this variation and safety factor in more detail in future videos.

FLOW TEST TIMING 

Flow tests can be performed prior to a system design, to help facilitate the design of a suppression system. 

Flow tests can be conducted periodically in order to determine any degradation in the overall water supply. This can be used by insurance carriers to reassess risk for a facility, or conducted every 5 years as recommended by NFPA 25 for private loop systems. 

SUMMARY

What is a flow test? It’s a test that measures pressure and flow at two different points which allows us to estimate the hydraulic curve of a water supply. 

Why conduct flow tests? To gather information about an existing water supply, to be sure that what is available is greater than what is required for a suppression system to operate sufficiently. 

For Frank Orset, I'm Jeff Kelm, this is MeyerFire University.