McDonnell & Miller 339500 Valve Assembly and Gasket

As a veteran tech, you know that keeping a boiler receiver tank at the correct level is non-negotiable. The McDonnell & Miller 339500 Valve Assembly, also known as the SA21-6 replacement valve, is the critical internal component for Series 21 and 221 make-up water feeders. This assembly provides proportional feed action and features a soft seat design to ensure a positive seal, preventing unwanted overfilling. When you are out on a service call and finding that the water feeder is sticking or bypassing, swapping in the SA21-6 valve kit is the fastest way to restore low water protection and professional-grade performance. This complete assembly includes the housing gasket and valve body gaskets required for a leak-free installation on the 5-3/4 inch bolt circle flange. Built for rigorous commercial boiler maintenance, this part handles a maximum water supply pressure of 150 psi and vessel pressures up to 35 psi, ensuring reliable steam boiler water level control across a variety of hydronic configurations.

• Direct Fit Compatibility: Specifically engineered for McDonnell & Miller Series 21 and Series 221 mechanical water feeders.
• Full Gasket Set Included: Comes with the 847-26 head gasket, 21-27 bracket gasket, and 21-12 valve body gasket for a complete seal.
• Durable Sealing: High-quality soft seat valve ensures a tight shut-off even in high-demand HVAC make-up water systems.
• Field-Proven Reliability: Trusted by contractors for boiler receiver tank applications where consistent proportional feeding is required.

Common Questions

Is the 339500 identical to the SA21-6 model?
Yes, the McDonnell & Miller 339500 is the exact part number for the SA21-6 valve assembly. They are interchangeable and designed for the same 21 Series feeders.

Can I use this valve assembly for a Series 25-A feeder?
No, the SA21-6 valve is technically specified for the Series 21 and 221. For 25-A units, you typically need the SA25A-6 assembly to ensure proper valve linkage alignment.

What are the maximum pressure ratings for this assembly?
This assembly is rated for a maximum supply pressure of 150 psi and a maximum vessel pressure of 35 psi. Exceeding these limits can compromise the proportional feed action.

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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.