Which option is not part of the 20% rule when selecting a pump?

• A. Agitation capacity
• B. Desired nozzle output
• C. Loss of pump capacity
• D. Tank diameter

Answer: (D)

When sizing a pump for spraying, you want enough flow to meet the nozzle’s requirements while also accounting for factors that reduce the actual delivered flow. The 20% rule is a practical cushion: you estimate the nozzle output you need and then add about 20% to cover inefficiencies and additional demands from the system.

Agitation capacity matters because you need enough flow to keep the spray mix uniform. If agitation is weak, the mixture can settle or separate, which can effectively reduce the usable flow and make accurate application harder. This need for reliable agitation pushes the required pump capacity upward.

The desired nozzle output sets the target flow you must achieve through the system. If you want a certain gallons-per-minute at the nozzle to get the correct application rate, the pump must be capable of delivering at least that much, considering the pressure at which you operate.

Loss of pump capacity accounts for the realities of real-world piping, filters, fittings, and height differences that steal some flow before it reaches the nozzle. The 20% add-on helps ensure the pump can still meet the nozzle requirement after these losses.

Tank diameter does not influence the pump’s required flow or the 20% overhead. It affects how much liquid you can mix and hold, not how much you need to spray per minute. So the element not part of the 20% rule is tank diameter.