Which statement correctly distinguishes dynamic pressure from static pressure in irrigation calculations?

Which statement correctly distinguishes dynamic pressure from static pressure in irrigation calculations?

• A. Dynamic pressure is measured with system off.
• B. Dynamic pressure equals static pressure when no head loss.
• C. Static pressure is greater than dynamic pressure always.
• D. Dynamic pressure is present when water is flowing and includes head loss.

Answer: (D)

Dynamic pressure is the portion of pressure that arises from moving water. It only exists when there is flow, and as water travels through a pipe, energy is spent overcoming friction, fittings, and elevation changes—these are head losses along the path. In irrigation calculations, you’re often concerned with how much pressure remains to push water through the laterals after those losses. The statement that dynamic pressure is present when water is flowing and includes head loss captures both of these ideas: flow creates dynamic energy, and head losses along the route affect how much pressure energy remains to drive the flow. If the system is off, there’s no dynamic pressure because there’s no flow. Static pressure isn’t guaranteed to be greater than dynamic pressure, since high flow can make velocity head substantial. And dynamic pressure isn’t simply the same as static pressure when there’s no head loss.

Dynamic pressure is the portion of pressure that arises from moving water. It only exists when there is flow, and as water travels through a pipe, energy is spent overcoming friction, fittings, and elevation changes—these are head losses along the path. In irrigation calculations, you’re often concerned with how much pressure remains to push water through the laterals after those losses. The statement that dynamic pressure is present when water is flowing and includes head loss captures both of these ideas: flow creates dynamic energy, and head losses along the route affect how much pressure energy remains to drive the flow.

If the system is off, there’s no dynamic pressure because there’s no flow. Static pressure isn’t guaranteed to be greater than dynamic pressure, since high flow can make velocity head substantial. And dynamic pressure isn’t simply the same as static pressure when there’s no head loss.