UNF Check Valves | McMaster-Carr

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30 Products

About Backflow-Prevention Valves

For Use With: Air, Nitrogen, Water
Ball Material: 304 Stainless Steel
Seal Material: See table

With a shorter end-to-end length than other check valves, these fit in tight spaces. They open to allow flow in one direction and close when flow stops or reverses.

303 stainless steel valves are more corrosion resistant than brass valves.

Flow coefficient (Cv) is the amount of water (in gallons per minute) at 60° F that will flow through a fully open valve with a difference of 1 psi between the inlet and the outlet.

For technical drawings and 3-D models, click on a part number.

UNF Female Inlet × UNF Female Outlet

Female Inlet × Female Outlet

Brass Body
Thread Size	Flow Coefficient (Cv)	Max. Pressure	Min. Opening Pressure, psi	Temperature Range, °F	End-to-End Lg.		Each
304 Stainless Steel Seal
10-32	0.081	125 psi @ 70° F	2	35° to 150°	13/16"	0000000	000000
303 Stainless Steel Body
304 Stainless Steel Seal
10-32	0.081	125 psi @ 70° F	2	35° to 150°	13/16"	0000000	00000

Welding Gas Check Valves for Regulators

Stop the reverse flow of gas in your regulator. Check valves do not stop flashbacks.

Max. Pressure, psi				Male Hose Connection			Male Pipe Connection
Oxygen	Acetylene	Hydrogen	Propane	Thread Direction	Thread Size	Thread Type	Thread Direction	Pipe Size	Thread Type	Material		Each
125	__	__	__	Right Hand	9/16"-18	UNF	Right Hand	1/4	NPT	Brass	000000	000000
__	50	50	50	Right Hand	9/16"-18	UNF	Left Hand	1/4	NPT	Brass	000000	00000

Welding Gas Check Valves for Torches

Stop the reverse flow of gas in your torch. Check valves do not stop flashbacks.

Max. Pressure, psi				Male Hose Connection			Female Hose Connection
Oxygen	Acetylene	Hydrogen	Propane	Thread Direction	Thread Size	Thread Type	Thread Direction	Thread Size	Thread Type	Material		Each
125	__	__	__	Right Hand	3/8"-24	UNF	Right Hand	3/8"-24	UNF	Brass	000000	000000
125	__	__	__	Right Hand	9/16"-18	UNF	Right Hand	9/16"-18	UNF	Brass	000000	00000
__	50	50	50	Left Hand	3/8"-24	UNF	Left Hand	3/8"-24	UNF	Brass	000000	00000
__	50	50	50	Left Hand	9/16"-18	UNF	Left Hand	9/16"-18	UNF	Brass	000000	00000

Welding Gas Flashback Arresters for Regulators

Standard and High Flow

Quick Disconnect

Attach these arresters to the outlet connection of a regulator on a torch that cuts steel up to 11" thick. Arresters extinguish flames and have a check valve to stop reverse gas flow. They are reusable; resetting is not required after flashback.

Arresters with right-hand threads are for use with oxygen. Arresters with left-hand threads are for use with acetylene, hydrogen, and propane.

High-flow arresters give you twice the airflow rate compared to standard flashback arresters when they’re used at the same inlet pressure. They are often used with larger torch tips.

Quick-disconnect arresters have a fitting that connects and disconnects them from your torch, so you don't have to thread these arresters on and off with a wrench.

Right-Hand Threads—UNF Male × UNF Female

Standard
Thread Size	Max. Pressure for Oxygen, psi	Material	Specifications Met		Each
3/8"-24	143	Brass	EN 730, ISO 5175	0000000	000000
9/16"-18	143	Brass	EN 730, ISO 5175	00000000	00000
High Flow
9/16"-18	143	Brass	EN 730, ISO 5175	00000000	000000
7/8"-14	143	Brass	EN 730, ISO 5175	00000000	000000
Quick Disconnect
9/16"-18	143	Brass	EN 561, ISO 7289	00000000	000000

Left-Hand Threads—UNF Male × UNF Female

	Max. Pressure, psi
Thread Size	Acetylene	Hydrogen	Propane	Material	Specifications Met		Each
Standard
3/8"-24	15	50	50	Brass	EN 730, ISO 5175	0000000	000000
9/16"-18	15	50	50	Brass	EN 730, ISO 5175	00000000	00000
High Flow
9/16"-18	15	50	50	Brass	EN 730, ISO 5175	00000000	000000
7/8"-14	15	50	50	Brass	EN 730, ISO 5175	00000000	000000
Quick Disconnect
9/16"-18	15	50	50	Brass	EN 561, ISO 7289	00000000	000000

Right-Hand and Left-Hand Threads—UNF Male × UNF Female

	Max. Pressure, psi
Thread Size	Oxygen	Acetylene	Hydrogen	Propane	Material	Specifications Met		Pair
Standard
9/16"-18	143	15	50	50	Brass	EN 730, ISO 5175	00000000	0000000

Welding Gas Flashback Arresters for Torches

Standard and High Flow

Quick Disconnect

These arresters attach directly to torches that cut steel up to 8" thick. They extinguish flames and have a check valve to stop reverse gas flow. They are reusable; resetting is not required after flashback.

Arresters with right-hand threads are for use with oxygen; arresters with left-hand threads are for use with acetylene, hydrogen, and propane.

High-flow arresters give you twice the airflow rate compared to standard flashback arresters when they’re used at the same inlet pressure. They are often used with larger torch tips.

Quick-disconnect arresters have a fitting that connects and disconnects them from your torch, so you don't have to thread these arresters on and off with a wrench.

With Right-Hand Threads

Male Hose Connection		Female Hose Connection
Thread Size	Thread Type	Thread Size	Thread Type	Max. Pressure for Oxygen, psi	Material	Specifications Met		Each
Standard
9/16"-18	UNF	9/16"-18	UNF	143	Brass	EN 730, ISO 5175	00000000	000000
High Flow
3/8"-24	UNF	3/8"-24	UNF	143	Brass	EN 730, ISO 5175	0000000	00000
9/16"-18	UNF	9/16"-18	UNF	143	Brass	EN 730, ISO 5175	00000000	000000
7/8"-14	UNF	7/8"-14	UNF	143	Brass	EN 730, ISO 5175	00000000	000000
Quick Disconnect
9/16"-18	UNF	9/16"-18	UNF	143	Brass	EN 561, ISO 7289	00000000	00000

With Left-Hand Threads

Male Hose Connection		Female Hose Connection		Max. Pressure, psi
Thread Size	Thread Type	Thread Size	Thread Type	Acetylene	Hydrogen	Propane	Material	Specifications Met		Each
Standard
9/16"-18	UNF	9/16"-18	UNF	15	50	50	Brass	EN 730, ISO 5175	00000000	000000
High Flow
3/8"-24	UNF	3/8"-24	UNF	15	50	50	Brass	EN 730, ISO 5175	0000000	00000
9/16"-18	UNF	9/16"-18	UNF	15	50	50	Brass	EN 730, ISO 5175	00000000	000000
7/8"-14	UNF	7/8"-14	UNF	15	50	50	Brass	EN 730, ISO 5175	00000000	000000
Quick Disconnect
9/16"-18	UNF	9/16"-18	UNF	15	50	72	Brass	EN 561, ISO 7289	00000000	00000

With Right-Hand and Left-Hand Threads

Male Hose Connection		Female Hose Connection		Max. Pressure, psi
Thread Size	Thread Type	Thread Size	Thread Type	Oxygen	Acetylene	Hydrogen	Propane	Material	Specifications Met		Pair
Standard
9/16"-18	UNF	9/16"-18	UNF	143	15	50	50	Brass	EN 730, ISO 5175	00000000	0000000

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About Backflow-Prevention Valves

Compact Threaded Check Valves

Welding Gas Check Valves for Regulators

Welding Gas Check Valves for Torches

Welding Gas Flashback Arresters for Regulators

Welding Gas Flashback Arresters for Torches