When it comes to protecting fire sprinkler systems from over-pressurization, pressure relief valves are a key component. But for years, there’s been confusion about what the pressure rating on these valves actually means, especially when it comes to the opening and closing pressures.
With the release of the 2025 edition of NFPA 13, that confusion is finally being addressed. New language in the handbook offers long-awaited clarity, helping system designers, inspectors, and maintenance personnel better understand how relief valves are supposed to perform.
The 2025 edition of NFPA 13 finally adds clarity.
What Changed in NFPA 13 (2025)?
In Chapter 8, A.8.1.2.1, of the 2025 handbook, new explanatory language to help system designers and inspectors understand relief valve behavior has been added:
“It is important to note that the pressure rating of the relief valve indicates an operating range of pressure for both opening and closing of the valve. Standard relief valves are required to open in a range of pressure between 90% and 105% of their rating. The valves are required to close at a pressure above 80% of that rating.”
What Does This Mean?
Let’s say you’re using a 175 psi-rated relief valve. According to this updated guidance:
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- The valve must open somewhere between 158 psi (90%) and 184 psi (105%).
- It must close once the pressure drops below the opening point, but not fall below 140 psi (80%).
- This clarification is especially important during testing and troubleshooting. Seeing a 175 psi valve open at 160 psi and close at 145 psi may appear to be a problem, but it’s within the expected operating range.
UL and FM Requirements for Relief Valves
NFPA’s new guidance reflects, but does not override, the standards established by UL (Underwriters Laboratories) and FM Approvals, which independently certify relief valves:
UL Standard:
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- Valves must open at no more than 105% of their rated pressure.
FM Standard:
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- Valves must open at no less than 85% of the rating.
- No field adjustment to the factory-set pressure.
- Any optional external “handle” (potentially used for flushing debris) will not affect the set pressure.
These certifications ensure reliability across a range of conditions and align closely with the ranges now clarified in the NFPA 13 annex.
Why no field adjustment?
To ensure consistent, reliable performance and eliminate the risk of improper adjustment in the field, reducing liability and improving safety across the board.
Why This Matters
Relief valves protect wet fire sprinkler systems against pressure build-up that could damage pipes, valves, or fittings. Without clearly defined expectations for opening and closing behavior, inspectors and facility managers might misinterpret normal function as a defect. Before this inclusion, many professionals believed that a 175 psi valve needed to open exactly at 175 psi. That led to installation mistakes and confusion during inspections.
With the 2025 clarification:
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- Designers understand what performance range to specify the correct pressure relief valve PSI.
- Installers and inspectors know how to verify correct operation.
- Facility managers can trust that listed valves operate within code, even when they open or close slightly above or below the rated number.
Best Practices
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- Always confirm you are using listed relief valves. These certifications are crucial for code compliance and performance.
- If a mistake was made during installation, check the percentage range to help determine the correct pressure relief valve PSI for your system.
- Verify that your system pressure doesn’t routinely exceed 80% of the valve rating, or you may experience frequent discharges.
- Never attempt to adjust valves in the field—they’re factory-set for a reason.
The new 2025 edition of NFPA 13 helps demystify how relief valves are meant to perform. Aligning expectations with other published standards, it promotes consistency across the industry. If you’re using AGF’s UL-listed 7000L pressure relief valves, you can rest assured they meet these requirements and are designed to function exactly as outlined in this updated guidance.