A line pressure regulator must be of the positive shut-off type when the inlet supply pressure exceeds which threshold?

A line pressure regulator must be of the positive shut-off type when the inlet supply pressure exceeds which threshold?

• A. 0.5 psig (3.5 kPa)
• B. 1.0 psig (7 kPa)
• C. 0.1 psig (0.7 kPa)
• D. 2.0 psig (14 kPa)

Answer: (A)

The key idea is that some regulators are built to seal completely when they’re shut, while others can still leak a little past the seat. A line regulator that could be exposed to any significant upstream pressure needs to be able to stop all flow, not just throttle it, to prevent gas from leaking downstream or back toward the supply when there’s no demand. When the inlet supply could exceed 0.5 psi, a positive shut-off type is required because higher upstream pressure increases the potential for leakage through a non–positive shut-off regulator. The positive shut-off design provides a tight seal that fully closes the path to the downstream side, ensuring no gas flows or leaks if the downstream side is shut or not drawing gas. That safety feature is why the threshold is set at 0.5 psi.

The key idea is that some regulators are built to seal completely when they’re shut, while others can still leak a little past the seat. A line regulator that could be exposed to any significant upstream pressure needs to be able to stop all flow, not just throttle it, to prevent gas from leaking downstream or back toward the supply when there’s no demand.

When the inlet supply could exceed 0.5 psi, a positive shut-off type is required because higher upstream pressure increases the potential for leakage through a non–positive shut-off regulator. The positive shut-off design provides a tight seal that fully closes the path to the downstream side, ensuring no gas flows or leaks if the downstream side is shut or not drawing gas. That safety feature is why the threshold is set at 0.5 psi.