Fire Flow Tests, How & Why

  • August 17, 2016

Fire Flow Tests, also known as Hydrant Flow Tests can be performed for several different reasons.


In general, fire flow tests are conducted on fire hydrants to determine the water availability.

There are multiple reasons why a flow test could need to be performed, below is a list of several of these reasons:

  • To determine water availability in planning for firefighting activities.
  • To determine water availability for the design of fire sprinkler systems.
  • To determine water availability for the design of domestic water systems.
  • To evaluate development of water main extensions.
  • To evaluate system improvements and replacements.
  • To determine the general condition of the water distribution system by detecting closed valves.

Fire flow testing produces accurate water data which can be used for various purposes. Fire Fighting Agencies use this water data for training, planning and marking hydrants. This water data is also used for water system planning and design. Municipalities also use the water data to simulate high flow conditions, to determine pressure and flow-producing capabilities of the water distribution system and for calibration of hydraulic models.


How often do Fire Flow Tests need to be performed on hydrants?

  • AWWA recommends flow testing all areas at least every 10 years (AWWA M17, chapter 6).
  • NFPA requires flow testing of underground and exposed piping at least once every 5 years (NFPA 25, Table, 2014).

How are Fire Flow Tests performed?

There are two types of Fire Flow Tests:

  • Main Capacity Test determines the water supply availability in the water main. If you are designing a fire sprinkler system, use this test (residual hydrant + separate downstream flow hydrant).
  • Hydrant Capacity Test determines the flow-rate available from the hydrant and if it will deliver in a fire emergency situation. If you are performing fire flow tests of hydrants, use this test (residual hydrant and flow hydrant are the same one).


For the purpose of this Blog we will only discuss how to perform a Main Capacity Flow Test, which is the two hydrant flow test. A Main Capacity Test evaluates the water supply of the fire main at the location of the test hydrant. The information derived from this test is used by city planners and contractors to consider the water supply for general use and fire sprinkler systems.


At the test hydrant (pressure hydrant, static/residual hydrant):

  1. Attach gauge cap to test hydrant. Tighten all other caps.
  2. Open test hydrant, vent air from hydrant body through the valve on the gauge cap assembly. Close it when air is vented.

At the flow hydrant

  1. Set the Little Hose Monster™ with gauge to the Pitotless Nozzle™ in an appropriate location for flowing water.
  2. Attach Remote Reader and gauge to the Pitotless Nozzle.
  3. Attach hydrant gate valve to the hydrant and close the gate valve.
  4. Tighten other caps.
  5. Attach the hose to the Pitotless Nozzle and Little Hose Monster assembly.

Conduct the test

  1. Record static pressure reading from gauge cap.
  2. Slowly open hydrant using the gate valve to purge air from the hydrant. When hydrant is full of water, open gate valve to desired flow-rate (usually full open).
  3. When the flow-rate stabilizes,
  4. Record nozzle pressure from the remote reader.

and at the same moment

At the test hydrant

  1. Record the residual pressure reading from the gauge cap.

At this point, the test is complete.

  1. Slowly close gate valve on flow hydrant, then close the hydrant. Remove test equipment from hydrant. Replace and tighten cap. If the hydrant is a dry barrel type, note that water drains properly from the hydrant.
  2. Record the number of minutes that water was flowing. This can be used to account for the amount of water used during the flow test.

At the test hydrant

  1. Close the hydrant. Remove gauge cap and replace hydrant cap. If the hydrant is a dry barrel type, note that water drains properly from the hydrant.

The information collected from this test can be used to predict flow-rates and residual pressures.

Now you know the How & Why of Fire Flow Tests a valuable tool in the engineer’s arsenal.


About the Author: Dwayne Johnson

Mr. Johnson brings over 25 years of experience in the industry and a majority of his experience is with design build contractors preparing detailed installation drawings and calculations.  His expertise is in fire protection, plumbing and all aspects of mechanical systems design.  

  • August 17, 2016