Which valve type is designed to vent air and prevent vacuum in irrigation lines?

• A. Check valve
• B. Quick coupling
• C. Hydrometer
• D. Air/vacuum relief

Answer: (D)

Air in irrigation pipes can create air locks and vacuum that hinder water flow. An air/vacuum relief valve is designed to vent trapped air to the atmosphere and allow a vacuum to be relieved, especially at high points in the line. When the system fills or experiences pressure changes, it opens to let air escape and then closes once water reaches it, preserving the water column and preventing flow interruption or pipe damage from vacuum. The other devices don’t serve this purpose: a check valve stops backflow but doesn’t vent air; a quick coupling is for connecting hoses; a hydrometer measures flow or pressure.