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#51 - What is a Hydrant Pressure Test?

Posted by Jason Hugo & Cameron Sharp on 6/24/2016 to Fire Hose
In the event of a fire emergency, reliable sources of water are essential. Hydrant pressure tests ensure this reliability by determining the pressure and rate of flow at any point in a city’s water distribution system. This is accomplished through measuring static (non-flowing) and residual (flowing) pressure, as well rate of discharge (GPM) of each fire hydrant. Read on as we describe why hydrant pressures tests are important, who performs them, and how they’re carried out.

Why are hydrant pressure tests important?

As previously mentioned, these hydrant pressure tests ensure the performance of a city’s water distribution system. The data that is collected during these tests is used for several important things. First, it leads to discoveries of heavy pipe-wall deposits because reduced rates of flow often stem from issues with infrastructure. Second, this data is vital for properly constructing fire sprinkler systems for commercial and residential structures. Incorrect readings can lead to underdeveloped systems which then require additional fire pumps or expensive overhaul of pipe fitting.  

Who performs them?

Hydrant pressure tests are carried out by city officials and professional contractors; typically every five years a city tests their distribution system. They follow strict guidelines and regulations set by the National Fire Protection Association (NFPA) when gathering data. The same personnel, when finished, then mark the fire hydrants using a color coding system, as demonstrated in the table below. The color system is an efficient way to notify fire departments of the water supply’s strength. These hydrants are categorized according to their flow’s GPM (gallons per minute), as illustrated in the table below:
Conducting a hydrant pressure test

Before beginning the test, you’re going to need several pieces of equipment. The first is a hand-held Pitot gauge. This instrument is what you will use to take pressure and rate of flow readings. You will also want to have an outlet-nozzle cap that’s outfitted with a pressure gauge; it goes right onto the residual hydrant. It is important to measure the inside diameter of each flow hydrant’s outlet nozzle, and to do that you’ll want to have a ruler on-site as well. Finally, a hydrant wrench is required to operate residual hydrant and flow hydrants.  

Provided below are 8 highly useful steps for executing a single-hydrant pressure test:

1. Determine test area by picking a hydrant downstream and closest to the building’s supply line for pressure readings
2. Next, select a hydrant further downstream as your secondary flowing hydrant to provide pitot readings 
3. Remove the nozzle cap of the pressure hydrant and add pressure gauge to its outlet
4. Open its valve completely and gather static pressure reading (Water should not be flowing)
5. Then, open the flowing hydrant’s valve. Always being cautious of nearby obstacles and traffic. A diffuser may be useful. 
6. After 30 seconds of steady flow and the pressure needle stabilizes, record the residual pressure from the hydrant’s pressure gauge. 
7. Following that, use a Pitot gauge to measure rate of discharge 
8. Close the hydrant slowly, as well as all valves involved. Check for leaks and ensure hydrants are back to working condition.

A critical piece of equipment required for a hydrant flow test is the Pitot gauge. For a detailed introduction to the Pitot gauge, continue on. When purchasing a pitot gauge to meet your job it’s important to consider several things. The working conditions that come with using a Pitot gauge, make positive grip a must. It is important to make sure it is light, but firm in your grip. A rotating pitot gauge can also make it easier to read measurements, and quick disconnect fitting make draining the system much faster. 
QRFS offers a wide selection of Pitot gauges. Our gauges come with all the aforementioned features and more! From our Inspector’s Choice Pitot gauge, which weighs only 14 ounces and features a 360-degree rotating N.I.S.T. –certified Ashcroft gauge, to our Pitot tube and gauge kit, you can’t go wrong. Visit us today and start browsing. 

*For a detailed version of these steps, and how to use a Pitot gauge visit blog #46 – How to Use a Pitot Gauge for Hydrant Flow Testing.

This blog originally posted by Jason Hugo and Cameron Sharp at QRFS.com/blog on June 24, 2016. If you like what you've read, check us out at Facebook.com/QuickResponseFireSupply or at Twitter @QuickRsponseFS.

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