BOOK: Blue Book II SECTION: Hydrant Flow Testing Pg 1 of 2

HYDRANT FLOW TESTING

Fire flow tests are made to determine the rate of water flow available for fire fighting. Every officer and pump operator must know the overall capacity of the water system and its flow in given areas. Fire flows are very important information when pre-planning any area of our city for fire fighting.

  1. Flow Test Precautions
  2. Whenever possible, the test should take place sometime between 0900 and 1700, the period of normal water demand. Keep in mind that water tests in the area of laundries and food or beverage plants may have to scheduled at times when they would be least affected by muddy or roily (when sediment or rust has been disturbed) water.
  3. Before the field work begins, plan in detail just how each test will be conducted, including:
  4. The hydrants to be used in the test, and their designations as Test and Flow Hydrants.
  5. The responsibilities of each firefighter.
  6. A review of previous tests, if available, to find any unusual readings or problems.
  7. Check to see where the flowing stream of water from the hydrant will go and make certain that the discharge does not damage private property or flood yards and basements.
  8. NEVER flow a stream of water across a busy street without first taking proper measures to warn and slow traffic.
  9. Under no circumstances flow a stream of water into a street during cold winter weather unless drainage and temperatures are such that there will be no hazard to traffic due to freezing. A good rule to follow is this: If in doubt, don't flow.
  10. Open and close hydrants slowly to prevent water hammer in the water mains.
  11. The Two Hydrants
  12. Test Hydrant
  13. The static pressure is read from this hydrant.
  14. The residual pressure is read from this hydrant.
  15. The available flow being obtained is for this hydrant.
  1. Flow Hydrant
  1. This is the hydrant next to the test hydrant, situated in the line of the normal water flow in the main.
  2. The normal flow will always be from large mains to smaller mains in a circulating system.
  3. The Flow Hydrant is the one from which water will actually flow during the test.
  1. Definitions
  2. Static Pressure

Theoretically, this is the water pressure in the main when no water is flowing or moving. Since some water Is almost always being drawn from city mains for domestic or manufacturing use, this 100% quiescent condition is almost never achieved. Generally the pressure reading with no test water flowing will be accurate enough to serve as the test static pressure.

  1. Residual pressure

When water is withdrawn from a water main during a flow test, the static pressure drops to a lower figure. This is residual pressure. The more water withdrawn, the lower the pressure drops. Static and residual pressures are read from the same gauge located on the test hydrant.

  1. Pitot tube and Gauge

The Pitot tube will measure the velocity of the stream from the open hydrant butt in pounds per square inch (Psi).

  1. Tools For Testing
  1. Pitot tube with pressure gauge
  2. Hydrant cap with pressure gauge
  3. Hydrant wrenches
  4. Clipboard
  1. Conducting a Flow Test
  1. Test Hydrant
  2. Remove one 2 1/2" cap and flush
  3. Attach the cap with the pressure gauge to the hydrant
  4. Open hydrant slowly and allow air to bleed out the petcock
  5. Close petcock and record the static pressure reading
  1. Flow Hydrant
  1. Remove one 2 1/2" cap and flush
  2. If the pressure drop is less than 10 psi on the test hydrant, other butts must be opened - do not use the steamer butt, you must use the other 2 1/2" butts on the hydrant - if the pressure still has not dropped enough, open another hydrants 2 1/2" butts
  3. When the water flow is clean, insert the Pitot gauge into the stream
  1. Open the petcock and drain all water from the air chamber and close the petcock
  2. Attach the blade to the Pitot gauge assembly so the blade is in the horizontal position and the gauge is elevated slightly above the horizontal position (doing this creates an air chamber in the Pitot gauge assembly to get a reading with less fluctuation on the pressure gauge).
  3. Put the blade into the center of the stream holding the blade approximately 1 1/4" awayfrom the hydrant butt
  4. Keep the blade horizontal while taking a reading
  5. Record the pressure reading from the Pitot gauge
  1. If the needle fluctuates, take a reading in the middle of the high and low marks
  2. Test Hydrant
  1. Record the residual pressure
  2. The static pressure must drop at least 10 psi for the residual pressure reading
  3. Close the hydrant slowly and be sure it is drained
  4. Flow Hydrant
  1. Close hydrant slowly and be sure it is drained
  1. Enter the readings into the computer program to find the gallons per minute available for the test hydrant
  2. Some Pointers to Remember
  1. Remember that you're dealing with substantial pressures, that water is noncompressible, and that safety of personnel and equipment must be your constant concern.
  2. Always stand behind the hydrant when opening, as caps have been known to violently blow off.
  3. It's a good idea to count the turns of the hydrant wrench when opening a hydrant to its full-open position. Then when the hydrant is shut down, you can count the turns again to make sure you've closed the hydrant completely and don't have a stone trapped beneath the foot valve of the hydrant, which would block full closure. Foreign material can be frequently be flushed out by opening the hydrant a few turns and closing it again.
  4. If the water from the hydrant runs roily or discolored (indicating excessive sedimentation in the main), it's best to let the hydrant flow easily. You may have to shut it down a few turns until the water flows clear and clean. Sand and dirt can easily clog the tiny opening into a Pitot tube blade and even reach up into the gauge itself. When this happens, it is very difficult to clean out without damaging the blade or gauge.
  5. The firefighter who uses the Pitot tube blade should hold it firmly as he braces himself against the hydrant. This prevents the blade and gauge from being knocked out of his grasp if a stone is ejected from the flowing hydrant and strikes the blade.

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