Which of the following would happen if the vent port on a gas regulator is plugged?

• A. Nothing; this is normal operation
• B. Outlet pressure will be reduced
• C. Outlet pressure will increase
• D. Inlet pressure will be reduced

Answer: (B)

When a regulator operates, the vent path lets the internal chamber pressure escape to the atmosphere so the diaphragm can stay balanced against the spring and regulate the downstream (outlet) pressure at the set point. If the vent port is plugged, the regulator can’t relieve pressure from that internal chamber. The trapped pressure pushes the diaphragm toward the spring, narrowing the flow to the outlet and causing the downstream pressure to drop. The inlet (supply) pressure stays effectively the same, but the regulator can’t maintain the usual outlet pressure, so it is reduced.