In a hydraulic irrigation system, what action causes the valves to open?

• A. They close when pressure is released
• B. They open when the controller applies water pressure
• C. They open when the pressure is released
• D. They stay open regardless

Answer: (C)

In a hydraulic irrigation system, the valve actuator responds to how pressure in the control line changes. The valve is held closed by the control pressure; when the controller releases that pressure, a spring or the diaphragm’s return moves the mechanism to the open position, allowing water to flow to the zones. So the action that opens the valve is the release of pressure, not applying pressure. If pressure were applied to open it, it would work opposite to how these hydraulic actuators are designed, and the valve would tend to close when pressure is restored.