Milwaukee Valve 509 3/8" FNPT Bronze Swing Check Valve

3/8" FNPT Bronze Swing Check Valve

The Milwaukee Valve 509 is a bronze inline swing check valve with female NPT connections on both ends. It suits residential and light commercial plumbing where back-flow prevention is required in a compact 3/8-inch line. The valve mounts horizontally or vertically to match the piping layout. Builders needing a larger bore or a flanged connection will need a different model.

Sustained flow and pressure behaviour

The swing mechanism opens at a cracking pressure between .750 and 1.000 psi, allowing flow with minimal restriction once the disc is fully lifted. The bronze body and bronze seat tolerate continuous water pressure of 200 psi at 150 degrees Fahrenheit and withstand fluid temperatures up to 406 degrees Fahrenheit. The minimum operating temperature is -20 degrees Fahrenheit. Systems that regularly exceed these pressure or temperature limits require a higher-rated valve.

Installation notes and common issues

Female NPT threads accept standard 3/8-inch male pipe fittings; apply thread sealant and tighten to the fitting manufacturer's torque specification. The valve must be oriented so the flow arrow matches the system direction, otherwise the disc will not open. Debris in the line can prevent the swing disc from sealing, causing leakage; a strainer upstream reduces this risk. Bronze seats are not field-replaceable, so severe seat wear means replacing the entire valve.