Maxitrol M520-3/4 Gas Valve

The Maxitrol M520-3/4 Gas Valve is a 3/4-inch NPT modulating gas valve engineered specifically for atmospheric, indirect-fired burners used in commercial and industrial space heating. As a core component of the Selectra electronic gas flame modulation system, this valve provides instantaneous, non-fluctuating temperature control without the need for external mechanical activation, motors, or butterfly valves. The M520-3/4 modulator valve is electronically driven to maintain precise heat output, making it an essential HVAC gas valve replacement for systems requiring stabilized area heating and consistent process drying temperatures. Technically identical to the Maxitrol M520-66, this unit supports a maximum inlet pressure of 1/2 PSI and is rated for temperatures up to 200°F. It features a brass body and a counter-spring design optimized for negative pressure (pull-through) applications. Technicians should note that while this valve handles flame modulation, high-fire pressure must be set at the appliance regulator, as the M520 does not include an integral high-fire regulator.

Key Benefits

• Precise Modulation: Provides continuous, infinite flame adjustment for Selectra modulation systems, ensuring stable discharge air temperatures.
• Broad Compatibility: Direct 3/4" NPT replacement for M520-66 gas valves used in Middleby Marshall ovens and various atmospheric burners.
• Efficient Design: Operates without a motor, reducing mechanical wear and simplifying field service in high-demand heating environments.
• Industrial Durability: Rated for high-temperature resistance up to 200°F with a robust brass construction for long-term reliable performance.

Common Questions

How do I adjust the minimum fire on the M520-3/4?
The minimum fire (low fire bypass) is adjusted via the bypass screw under the cap. We recommend removing the #8 wire from the amplifier to drive the valve to minimum fire during the adjustment procedure to ensure a steady, even flame ribbon.

Is the M520-3/4 compatible with LP gas?
Standard M520 models are suitable for natural, manufactured, mixed, and liquefied petroleum (LP) gas-air mixtures. However, strictly LP-only applications may require the "H" suffix models (M520H) depending on specific manifold pressure requirements.

Can I use this valve to regulate high-fire pressure?
No. The M520 series valves do not have an internal high-fire regulator. Maximum high-fire manifold pressure must be set at the main appliance regulator or an upstream pressure regulator.

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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.