A flow test measures how much water a hydrant can deliver. Fire records each test, calculates the rated capacity at 20 PSI residual pressure, and assigns the NFPA 291 color class automatically.

Before you start: You need the hydrant's static pressure, residual pressure, pitot reading, and the outlet diameter you used. Get those readings on the apparatus before you sit down at the form.

Step by step

  1. Open the hydrant detail page.
  2. Click the Flow Tests tab.
  3. Click Add Flow Test.
  4. Fill in the form (see the field list below).
  5. Click Save.

What to enter

  • Test Date -- The day the test was performed.
  • Static Pressure -- The pressure in PSI with no water flowing.
  • Residual Pressure -- The pressure in PSI while water is flowing.
  • Pitot Reading -- The pitot gauge reading in PSI.
  • Outlet Diameter -- The diameter of the outlet you flowed from, in inches.
  • Outlet Type -- Smooth, square, projecting, or other. This sets the discharge coefficient used in the calculation.
  • Technician -- The person who performed the test.
  • Notes -- Anything worth noting, like a hydrant that was hard to open or a leak around the cap.

How the calculator works

As you enter the pressures and the outlet diameter, Fire calculates three things and shows them live:

  • Calculated GPM -- Flowing gallons per minute, from the formula Q = c * d squared * the square root of P.
  • Rated Capacity at 20 PSI -- The GPM the hydrant could deliver if the residual pressure dropped to 20 PSI, using the NFPA 291 projection.
  • NFPA Class -- A color badge based on the rated capacity:
    • Blue -- 1,500 GPM or more.
    • Green -- 1,000 to 1,499 GPM.
    • Orange -- 500 to 999 GPM.
    • Red -- Less than 500 GPM.

If you already know the GPM and would rather enter it directly, toggle Manual GPM on and type the number in. The class is still calculated.

Tips

  • If the residual pressure is below 20 PSI, the form shows a red warning. That hydrant is below the threshold NFPA uses for fire flow planning -- review it before relying on it.
  • The latest flow test for a hydrant appears as a summary card at the top of its detail page.