WETS Irrigation Technician Practice Exam

When the flow rate is kept the same, increasing the pipe diameter lowers the fluid velocity because Q = A v and A grows with D^2. Friction losses are driven by wall shear, which scales with velocity (in the common Darcy–Weisbach view, head loss goes with v^2). So as velocity drops, the friction loss drops even more strongly. In simple terms, a larger pipe gives the fluid more space to move, reducing the energy lost to friction. The result is a smaller friction loss for the same flow.