When PVC pipe is used for irrigation systems, which schedules must be used on the discharge sides and the supply sides of control valves?

When PVC pipe is used for irrigation systems, which schedules must be used on the discharge sides and the supply sides of control valves?

• A. Schedule 20 on discharge; Schedule 40 on supply
• B. Schedule 40 on discharge; Schedule 80 on supply
• C. Schedule 80 on discharge; Schedule 40 on supply
• D. Schedule 40 on both sides

Answer: (B)

The important idea is matching pipe strength to where the stress is highest around a control valve. The supply side (upstream of the valve) is exposed to the full system pressure and potential surges, so using Schedule 80 PVC provides a thicker wall and a higher pressure rating to resist rupture and damage near the valve. The discharge side (downstream) typically sees lower, controlled pressure once water has passed through the valve, so Schedule 40 is sufficient and more cost-effective. Hence, Schedule 80 on the supply side and Schedule 40 on the discharge side.

The important idea is matching pipe strength to where the stress is highest around a control valve. The supply side (upstream of the valve) is exposed to the full system pressure and potential surges, so using Schedule 80 PVC provides a thicker wall and a higher pressure rating to resist rupture and damage near the valve. The discharge side (downstream) typically sees lower, controlled pressure once water has passed through the valve, so Schedule 40 is sufficient and more cost-effective. Hence, Schedule 80 on the supply side and Schedule 40 on the discharge side.