Which statement best describes dynamic pressure and head in an irrigation system?

Which statement best describes dynamic pressure and head in an irrigation system?

• A. Dynamic pressure is the pressure when water is moving; head is the energy required to lift water.
• B. Dynamic pressure is the pressure when water is stationary; head is the height of the water column above the pipe.
• C. Dynamic pressure is the pressure when water is moving; head is the equivalent height of pressure; 1 psi equals about 2.31 feet.
• D. Dynamic pressure is the pressure drop across a valve; head is the maximum pressure in the system.

Answer: (C)

Dynamic pressure and head describe how moving water carries energy and how that energy can be expressed as a height of water. Dynamic pressure is the pressure that arises because water is moving—the velocity energy contributes to the pressure you measure in the line. Head is the energy expressed as an equivalent height of water; in hydraulics you can convert pressure to head using the relationship that 1 psi is about 2.31 feet of water. So the best statement says dynamic pressure is the pressure when water is moving, and head is the equivalent height of that pressure, with the psi-to-feet conversion. Some ideas you might see in other statements aren’t accurate: dynamic pressure isn’t tied to stationary water, and head isn’t just the height of a water column above the pipe or the system’s maximum pressure—it’s energy per unit weight that can be expressed as height, combining pressure, elevation, and velocity energy.

Dynamic pressure and head describe how moving water carries energy and how that energy can be expressed as a height of water. Dynamic pressure is the pressure that arises because water is moving—the velocity energy contributes to the pressure you measure in the line. Head is the energy expressed as an equivalent height of water; in hydraulics you can convert pressure to head using the relationship that 1 psi is about 2.31 feet of water. So the best statement says dynamic pressure is the pressure when water is moving, and head is the equivalent height of that pressure, with the psi-to-feet conversion.

Some ideas you might see in other statements aren’t accurate: dynamic pressure isn’t tied to stationary water, and head isn’t just the height of a water column above the pipe or the system’s maximum pressure—it’s energy per unit weight that can be expressed as height, combining pressure, elevation, and velocity energy.