In central supply systems using gas cylinders, each header shall have a ________ valve to prevent backflow and to permit service to the header.

In central supply systems using gas cylinders, each header shall have a ________ valve to prevent backflow and to permit service to the header.

• A. Check
• B. Relief
• C. Ball
• D. Bypass

Answer: (A)

Backflow prevention is the key idea here. A check valve is a one-way device that lets gas flow toward the header but automatically closes if pressure tries to push gas backward toward the cylinders or into other sources. This keeps the supply isolated from the header when pressures change or a bank is being serviced, preventing cross-contamination and protecting the gas supply. A relief valve is designed to vent excess pressure, not to stop reverse flow. A ball valve is a general shutoff without automatic backflow protection, and a bypass valve provides an alternate path rather than preventing reverse flow. So the appropriate valve is the check valve.

Backflow prevention is the key idea here. A check valve is a one-way device that lets gas flow toward the header but automatically closes if pressure tries to push gas backward toward the cylinders or into other sources. This keeps the supply isolated from the header when pressures change or a bank is being serviced, preventing cross-contamination and protecting the gas supply. A relief valve is designed to vent excess pressure, not to stop reverse flow. A ball valve is a general shutoff without automatic backflow protection, and a bypass valve provides an alternate path rather than preventing reverse flow. So the appropriate valve is the check valve.