H698 - Smith H698 Regulator-Mount Reverse Flow Check Valves (Pair)

Technical Overview of Smith H698 Reverse Flow Check Valves

The Smith H698 Reverse Flow Check Valves are precision-engineered safety devices designed to mitigate the risks associated with pressure imbalances in oxy-fuel welding and cutting systems. In industrial gas applications, a condition known as reverse flow can occur when a torch tip becomes obstructed or when one cylinder in a two-gas system empties while the other remains pressurized. This pressure differential can force the higher-pressure gas to travel back up the hose of the lower-pressure gas, potentially reaching the regulator and creating a volatile mixture. The H698 set is specifically designed to mount directly to the regulator outlets, serving as a primary barrier against this hazardous phenomenon.

Constructed from machined brass, these valves are built to withstand the rigors of industrial environments while maintaining the tight tolerances required for gas safety. The internal mechanism features a low-cracking-pressure spring that holds a valve seat open during normal flow conditions. However, should the downstream pressure drop or back-pressure occur, the valve is calibrated to close automatically when the outlet pressure falls below 1/2 PSIG. This rapid response effectively isolates the regulator from the hose, preventing the migration of mixed gases into the high-pressure equipment components.

The H698 set includes two valves: one designated for oxygen (Right-Hand threads, typically marked green) and one for fuel gas (Left-Hand threads, typically marked red or notched). Both utilize standard B-Size 9/16-18 connections, ensuring compatibility with the vast majority of North American industrial regulators. It is important to distinguish these devices from flashback arrestors; while check valves prevent the reverse flow of gas, they do not contain a flame barrier to stop a flame front. Therefore, they are often used in conjunction with torch-mount or regulator-mount flashback arrestors for a comprehensive safety solution. For systems requiring high flow rates, the H698 offers minimal flow restriction during normal operation, ensuring that flame characteristics remain stable during cutting or heating operations.

Installation of the H698 is straightforward, threading directly onto the regulator outlets before the hoses are attached. This positioning protects the regulator and cylinders from contamination and backflow originating anywhere downstream in the hose or torch assembly. Regular testing of check valves is recommended to ensure the internal springs and seals remain free of debris and function correctly under reverse pressure conditions.