Check Valve
A check valve is a mechanical valve that allows fluid (liquid or gas) to flow in only one direction and automatically prevents reverse flow (backflow) when flow stops or reverses. It opens under forward differential pressure (cracking pressure) and closes when downstream pressure exceeds upstream. In engineering, it is also called a non-return valve, one-way valve, or foot valve.
On a manufacturing shop floor, check valves are used anywhere reverse flow could create safety, quality, or equipment-damage risks. Common applications include compressed air and pneumatic tools, where pneumatic safety check valves at compressor outlets and branch lines prevent hose whip and uncontrolled air discharge, complying with OSHA 1926.302(b)(7). In hydraulic power units and presses, check valves prevent backflow from actuators into pump manifolds, maintaining hydraulic lock. In industrial water/coolant systems, they are installed in backflow preventer assemblies to protect potable water from contamination, per CSA-B64 series standards. For fire protection, single or double check valve type backflow preventers ensure sprinkler water cannot return to potable systems. Maintenance must ensure flow direction arrows match process flow, and preventive maintenance includes inspecting internal poppets and seating surfaces for wear and debris.
How is a check valve functionally different from a relief (safety) valve?
A check valve controls flow direction, opening when upstream pressure exceeds downstream by at least the cracking pressure, and closing when flow reverses. It is a passive, line-flow device. A relief/safety valve is an overpressure protection device that opens at a set pressure to vent or bypass fluid and protect systems from exceeding design pressure limits. Check valves do not provide overpressure protection and cannot substitute for relief valves.
How do BC code requirements around check valves at the building water service interface affect industrial facilities?
BC Plumbing Code requires a check valve at the building end of a water service pipe when the pipe is plastic suitable for cold water only. Once installed, the interior plumbing becomes a closed system, requiring thermal expansion protection (e.g., expansion tanks, relief valves) to avoid nuisance discharge or pipe rupture. Removal or bypassing such check valves during maintenance can place the facility out of compliance and increase backflow risk.
How should check valves be addressed in confined space and isolation procedures?
Check valves cannot be treated as positive isolation; they are automatic devices that can leak or fail open. Isolation for confined space entry must use lockable, verifiable isolation devices (e.g., double block and bleed, blind flanges) upstream and downstream. Any piping with check valves connected to the space should be depressurized and drained, and check valves should be assumed not tight and not relied upon to prevent ingress of fluids or gases.