A fire pump drafts water by sucking it from a reservoir or other body of water. This lets firefighters put out fires in rural areas, far from any hydrant or other piped supply. The main fire pump creates a vacuum; atmospheric pressures forces water from a source through a pipe and out a nozzle. A secondary pump adds extra pressure, forcing out greater quantities of water. When testing a pumps, technicians measure flow experimentally using pilot tubes or flow meters. You can calculate the theoretical flow velocity, however, from hose conditions and the pressure at the nozzle.
Things You'll Need
Find the square root of the nozzle's pressure, measured by a flow-meter in pounds per square inch. If water travels through the nozzle at 40 pounds per square inch: √40 = 6.32.
Square the nozzle's diameter, measured in inches. If the nozzle has a 1.5-inch diameter: 1.5² = 2.25.
Multiply together the answers from Step 1 and 2: 6.32 x 2.25 = 14.22.
Multiply the product from Step 3 by 30. The conversion constant "30" relates the units you've used and factors in the density of water. With this example: 14.22 x 30 = 426.6. This answer is the hose's flow velocity, measured in gallons per minute.
- University of Hawaii: Velocity and Discharge
- "Introduction to Fire Pump Operations"; Thomas B. Sturtevant; 2004
- Photo Credit Fire Hose image by Towards Ithaca from Fotolia.com
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