How can you identify an undersized mainline?

• A. By the color of the pipe.
• B. By observing excessive pressure loss and reduced flow when zones operate together; verify with flow and pressure measurements.
• C. By the age of the controller.
• D. By the soil moisture near the mainline.

Answer: (B)

The main idea is that the mainline has to carry the total water demand of the entire system. When several irrigation zones operate at once, the mainline is asked to deliver more water. If it’s undersized, the friction losses in that pipe become large enough that both the pressure drops and the flow rate fall short of what the system needs. You can identify this by watching how pressure and flow behave as more zones run: a noticeable, excessive pressure loss and reduced flow indicate the mainline isn’t sized to handle the combined demand. To confirm, take actual flow and pressure measurements along the mainline and at downstream points and compare them to the design values; a significant mismatch confirms undersizing. The other options don’t relate to the pipe’s ability to move the full system flow—color isn’t a reliable indicator, controller age doesn’t reflect pipe capacity, and soil moisture near the line doesn’t reveal sizing.