How to Select the Correct PSI for Your Pressure Relief Valves

Pressure relief valves are critical components in fire sprinkler systems, safeguarding the system by relieving excess pressure caused by supply surges or temperature fluctuations. Since the 2010 edition of NFPA 13, these valves have been mandatory for all wet pipe systems. Selecting the correct pressure relief valve for a specific system requires careful planning to ensure compliance and optimal performance.

Understanding NFPA 13 Requirements

NFPA 13 outlines the necessity of pressure relief valves to maintain system integrity:

• Relief Valve Specifications: Wet pipe systems must include a listed relief valve of at least 1/2 inch in size. The valve should operate at either 175 psi or 10 psi above the maximum system pressure, whichever is greater.
• Listing Requirements: A “listed” valve must meet standards set by third-party organizations like UL or FM, ensuring the valve’s reliability and suitability for fire sprinkler systems.
• Exception Clause: Relief valves are not required if auxiliary air reservoirs are installed to absorb pressure increases.

Key Factors in Selecting a Pressure Relief Valve

1. System Static Pressure: Determine the system’s desired static pressure and use it as a baseline for selecting the valve.
2. UL and FM Standards:?These organizations define the operational characteristics of relief valves. UL requires valves to open at a pressure no greater than 105% of their rating, and FM requires opening at no less than 85% of the rating. Both standards mandate valves close below the opening pressure to prevent constant discharge.

Calculating the Correct PSI for the Pressure Relief Valve

To select a suitable factory-set valve:

• Opening Pressure: Multiply the valve’s factory-set rating by 90%.
• Closing Pressure: Multiply the factory-set rating by 80%.

For example, a 175-psi rated valve opens at approximately 158 psi and closes at around 140 psi. This valve would be appropriate if the system’s static pressure is below 150 psi. However, for static pressures closer to 165 psi, a higher-rated valve may be necessary.

Avoiding Risks of Adjustable Relief Valves

While adjustable relief valves offer flexibility, they pose significant risks:

• Field Adjustments: These valves can be tampered with, potentially setting them outside the required pressure range, which violates FM Standards and compromises system safety.
• Debris and Maintenance: Adjustable valves often lack features like debris-flushing handles, increasing the likelihood of malfunctions and leaks.
• Testing Complications: Hydrostatic testing requires valves to be temporarily closed or installed after testing. Adjustable valves are often used closed in this process but not reopened, risking non-compliance with standards.

The Case for Factory-Set Relief Valves

Factory-set pressure relief valves are specifically designed for fire sprinkler systems, offering:

• Pre-Set Ratings: Ensuring accurate performance within the desired pressure range.
• Testing Compatibility: AGF’s 7000L pressure relief valve allows temporary isolation while the valve is installed for hydrostatic testing without altering its rating, keeping it compliant with FM requirements.
• Durability: Features like flushing handles to remove debris ensure long-term reliability.

When choosing a pressure relief valve, prioritize factory-set, listed models that meet NFPA 13 requirements and adhere to UL and FM standards. Proper planning and adherence to these guidelines ensure your fire sprinkler system operates safely and effectively, protecting lives and property. Selecting the correct pressure relief valve PSI eliminates potential risks and maintains compliance with the highest safety standards.

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