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Two brass check valves with 9/16-18 UNF fittings, left and right hand threads

Miller-Smith Equipment

Miller-Smith Equipment H698 Reverse Flow Check Valve Set 2 Pc

SKU CH-9FHY-RMEZ7

A two-piece reverse flow check valve set for regulator mounting, compatible with fuel gas and oxygen, featuring brass bodies with 9/16 in.-18 UNF connections and UL listing

  • TypeWelding Parts & Supplies
  • Prevents reverse gas flow with UL-listed check valves
  • Fits regulator mounts using 9/16 in.-18 UNF connections
  • Handles both fuel and oxygen with CGA 023 and CGA 022 inlets
  • Brass body resists corrosion for long service life
  • Includes two valves for complete torch setup

Miller-Smith H698 Check Valve Set

The Miller-Smith H698 is a two-piece reverse-flow check valve set designed for oxy-fuel welding systems. It mounts directly onto the regulator to prevent dangerous gas backflow during cutting or heating work. Professional welders and maintenance crews use it to meet safety requirements on fuel and oxygen lines.

Critical Specifications for Compatibility

Each valve has a 9/16 in. -18 UNF inlet and outlet with CGA 023 for fuel and CGA 022 for oxygen connections. The brass body carries a UL listing and accepts hose fitting size B. Left-hand threads on the fuel side and right-hand threads on the oxygen side prevent accidental cross-connection.

Installation Notes and Common Pitfalls

Thread the valves onto the regulator outlets by hand, then tighten with a wrench on the brass flats only. The most frequent error is reversing the fuel and oxygen valves because the thread directions differ. Leaks usually come from damaged UNF threads or missing sealing washers, not from the check mechanism itself.

Highlights

  • Prevents reverse gas flow with UL-listed check valves
  • Fits regulator mounts using 9/16 in.-18 UNF connections
  • Handles both fuel and oxygen with CGA 023 and CGA 022 inlets
  • Brass body resists corrosion for long service life
  • Includes two valves for complete torch setup

Specifications

TypeWelding Parts & Supplies
BrandSMITH EQUIPMENT

Questions about this item

What does the UL Listed marking mean when the valves are installed on a regulator?

UL Listed means the set has been tested to the applicable safety standard for oxy-fuel check valves and is approved for use on regulator outlets handling fuel gas and oxygen.

How do the 9/16‑18 UNF connections and CGA 022/023 inlets limit which regulators and hoses can be used?

The left‑hand 9/16‑18 UNF inlet with CGA 023 fits fuel‑gas regulators, the right‑hand 9/16‑18 UNF inlet with CGA 022 fits oxygen regulators, and both outlets accept standard B‑size hose fittings.

What clearance and thread engagement are needed to mount the brass bodies on a regulator?

Each valve body threads directly onto a 9/16‑18 UNF regulator outlet; the brass construction requires standard wrench flats and enough space for the check‑valve mechanism to operate without interference.

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