What is the function of a pressure regulating/sustaining valve?

• A. Maintains pressure by opening only as required to maintain the inlet port pressure
• B. Maintains pressure by staying fully open
• C. Diverts flow to waste
• D. Closes automatically on low pressure

Answer: (A)

Pressure regulating/sustaining valves keep system pressure at a chosen level by adjusting how much flow passes through. They don’t stay fully open or fully closed; instead, they respond to pressure changes and open only as needed to maintain the pressure at the inlet port within the desired range. When upstream pressure tends to rise, the valve throttles back; when it drops, the valve opens more to hold the set pressure. This modulation helps keep emitters and laterals operating consistently and protects components from pressure spikes. If a valve were to stay fully open, pressure could rise or fluctuate; diverting flow to waste isn’t part of normal regulation, and closing automatically on low pressure would starve the system.