A fire hydrant pressure test.

Hydrant pressure tests ensure adequate water supply to fire protection systems – and a pitot gauge is an essential tool for getting the job done

Reliable sources of water are essential in a fire emergency. 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 by measuring static (non-flowing) and residual (flowing) pressure, as well the rate of discharge in gallons per minute (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?

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

Who performs them?

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

  • Blue: 1,500 GPM or more; considered "Very good flow."
  • Green: 1,000-1,499 GPM; "Good for residential areas."
  • Orange: 500-999 GPM; "Adequate marginally."
  • Red: Below 500 GPM; "Inadequate."

For additional hydrant color classifications, check out an expanded table.

Conducting a hydrant pressure test

Before beginning the test, a life safety professional needs several pieces of equipment. The first is a hand-held pitot gauge. This instrument is used to take pressure and rate-of-flow readings. An outlet-nozzle cap that’s outfitted with a pressure gauge which goes right onto the residual hydrant is another key tool. It's also important to measure the inside diameter of each flow hydrant’s outlet nozzle, and a simple ruler can accomplish this task. Finally, a hydrant wrench is required to access hydrants to take residual and flow readings.

Here are 8 useful steps for executing a single-hydrant pressure test:

  1. Determine the test area by picking a hydrant that's downstream of and closest to the building’s supply line for pressure readings.
  2. Next, select a hydrant further downstream as a secondary flowing hydrant to provide pitot readings.
  3. Remove the nozzle cap of the pressure hydrant and add the 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 be cautious of nearby obstacles and traffic. A diffuser may be useful.
  6. After 30 seconds of steady flow and when the pressure needle stabilizes, record the residual pressure from the hydrant’s pressure gauge.
  7. Following that, use a Pitot gauge to measure the 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.

For a detailed version of these steps and how to use a pitot gauge, check out our blog: "How to Use a Pitot Gauge for Hydrant Flow Testing."

A pitot gauge is a critical piece of equipment for a hydrant flow test. When purchasing one to do the job correctly, it’s important to consider several things. Given the wet working conditions while using a pitot gauge, it should have a handle with a good grip. Make sure it can be held in a light but firm grasp while executing a test. A rotating pitot gauge can also make it easier to read measurements, and a quick disconnect fitting makes draining the system much faster.

QRFS pitot gauges come with all the aforementioned features and more! Our Inspector’s Choice Pitot gauge weighs only 14 ounces and features a 360-degree rotating, NIST–certified Ashcroft gauge and our pitot gauge parts and accessories include blades, handles, and quick-disconnect fittings.

If you have questions about this article or pitot gauges, call us at +1 (888) 361-6662 or email [email protected].

This blog was originally posted by Jason Hugo and Cameron Sharp at QRFS.com/blog on June 24, 2016, and updated on January 15, 2019. If you like what you’ve read, check us out on Facebook and Twitter.