In the horsepower calculation example, what is the weight in pounds per minute derived from the flow rate of 175 gpm?

• A. 7.4805
• B. 8.34
• C. 62.4
• D. 3.14

Answer: (B)

The key idea is converting a volumetric flow into a weight flow using the weight of water per unit volume. Water weighs about 8.34 pounds per gallon, so to relate flow rate in gallons per minute to pounds per minute you multiply by 8.34. In this context, the value 8.34 represents that pounds-per-gallon conversion factor used in the horsepower calculation. The other numbers are common unit conversions (gallons per cubic foot, pounds per cubic foot) or a mathematical constant, which aren’t the weight-per-volume factor needed here. So the weight-per-volume constant used for water is 8.34 pounds per gallon.