3.6 Flow Rates

Flow rates describe the speed at which water is flowing. They are described in gallons per minute (gpm). The following test is a simple way to observe a flow rate.

Use a large drum with a marked level to indicate a pre-measured 50-gallon volume. Begin filling the drum with a hose and at the instant that the water begins to fill the tank, start timing how long it takes with a precise stop watch (preferably to 1/100 of a minute). When the water level reaches the marked line, take the hose away, and stop timing. To calculate the flow rate of the water through the hose, divide the total volume by the total time it took to reach that volume. Suppose it took 3.55 minutes. 

50 gallons per 3.55 minutes (50/3.55)
50 รท 3.55 = 14.08
Flow rate = 14.08 gpm

If the stop watch has only seconds and minutes, the seconds can be converted into fractions (parts) of minutes. There are 60 seconds in 1 minute.


Select the correct answer(s) from the questions below: