This document discusses sizing pipes and valves for an irrigation system. It notes that the safety limit for pipe velocity is 5 feet per second and provides an example of sizing pipes in reverse from the critical circuit length farthest from the valve. In the example, 3/4 inch pipe is sized for the first section supplying one head, 1 1/4 inch pipe for two heads, 1 1/2 inch pipe for three heads, and 2 inch pipe for four heads to keep velocity below 5 feet per second for each section. The document advises sizing additional circuits by splitting into smaller sections for lower water volumes and smaller pipe sizes.