McDonnell & Miller 317353 Valve

The McDonnell & Miller 317353, specifically the Model TC-L Test-N-Check Lower Valve, is a critical component for contractors maintaining hydronic systems. Designed for hot water boilers, this 1" NPT valve is engineered to simplify ASME CSD-1 code-mandated testing of low water cut-offs (LWCO). By replacing standard 1" crosses in the equalizing lines, the TC-L allows for the isolation of the float chamber during blow-down procedures without requiring a full system drain. This boiler safety control part is rated for a maximum pressure of 160 psi and a maximum temperature of 250°F. During a test, the internal damper snaps shut upon the sudden rush of water, restricting flow and allowing the float chamber to evacuate rapidly. This ensures the cut-off triggers the burner shutdown as intended, verifying the hydronic heating system safety loop. Its design permits standard rod clean-out of the piping, preserving long-term reliability in high-sediment environments.

• Code Compliance: Streamlines the required ASME CSD-1 testing process for commercial and residential boilers.
• Labor Efficiency: Eliminates the need to drain and refill the entire heating system to test the low water cut-off.
• System Protection: Minimizes the loss of treated boiler water and reduces the introduction of fresh oxygenated water during maintenance.
• Serviceability: Retains the ability to perform manual rod clean-outs of equalizing lines through the valve body.
• Robust Design: Constructed to withstand high-pressure hydronic environments up to 160 psi.

What is the difference between the TC-U and TC-L valves?
The TC-U (Upper) valve features a built-in vacuum breaker to assist in rapid chamber evacuation, whereas the TC-L (Lower) valve acts as the primary restriction point for the lower equalizing line and typically houses the blow-down valve connection.

Can these valves be used on steam boiler systems?
No, the McDonnell & Miller 317353 is specifically rated and designed for hot water boiler applications. Steam systems require different testing and isolation configurations.

Does the TC-L valve change the footprint of the LWCO?
Yes, installing Test-N-Check valves in place of standard crosses will typically extend the low water cut-off approximately 2 inches further from the boiler tapping.

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.