How many gallons per minute must a pump deliver to supply 24 gallons per acre when treating an 8-foot swath at 10 mph?

• A. 3
• B. 4
• C. 5
• D. 6

Answer: (B)

The key idea is converting a spray rate from gallons per acre into a flow rate in gallons per minute by using how fast you move and how wide the spray swath is. You’re spraying 24 gallons for every acre, while moving at 10 mph with an 8-foot swath. First figure how many acres you cover per minute: at 10 mph with an 8-foot swath, you sweep about 9.696 acres per hour, which is 9.696 / 60 ≈ 0.1616 acres per minute. Multiply that by the application rate: 0.1616 acres/min × 24 gal/acre ≈ 3.88 gallons per minute. So the pump needs to deliver about 3.9 GPM, which is essentially 4 GPM when choosing from standard pump sizes.