McDonnell & Miller 250-3/4-15 Valve

The McDonnell & Miller 250-3/4-15 is a high-performance 3/4" NPT Pressure Relief Valve engineered for critical over-pressure protection in hydronic heating systems and storage tanks. Featuring a robust bronze body and seat, this valve is factory-set at 15 PSI with a substantial thermal discharge capacity of 515,000 BTU/hr. Designed to meet ASME Section IV code requirements for heating boilers, it utilizes an EPDM rubber diaphragm and seat disc to ensure a positive seal and consistent pop-off performance. The low differential pressure—only 3 PSI between opening and closing—prevents system short-cycling and minimizes water hammer caused by flash steam. With a maximum operating temperature of 250°F, the Part Number 181220 is the industry standard for contractors requiring a reliable, fail-safe boiler relief valve that maintains system integrity under peak thermal loads. Its threaded NPT connections allow for straightforward integration into existing manifold headers or vessel tappings.

• ASME Section IV Certified: Fully compliant with pressure vessel safety standards for commercial and residential hydronic applications.
• High BTU Rating: Manages up to 515,000 BTU/hr, providing a wide safety margin for high-efficiency boiler installations.
• Corrosion-Resistant Construction: Heavy-duty bronze body and EPDM internals resist scale buildup and thermal degradation.
• Flash Steam Protection: Specifically designed to minimize hammering and vibration during emergency discharge cycles.
• Low Blowdown Differential: Rapidly resets after a 3 PSI drop, conserving system fluid and preventing unnecessary pressure loss.

What is the maximum temperature rating for the McDonnell & Miller 181220?
This valve is rated for a continuous maximum water temperature of 250°F (121°C).

Can this 15 PSI relief valve be used in steam heating systems?
The Series 250 is specifically designed for liquid-phase hydronic heating systems and tanks. For low-pressure steam applications, verify that the capacity and set point align with your specific boiler’s nameplate and local mechanical codes.

What is the discharge capacity of the 250-3/4-15 model?
The valve is rated at 515,000 BTU per hour at its 15 PSI set point, as verified by ASME Section IV standards.

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Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.