SCUBA Valves FAQ
Thermo™ SCUBA valves are manufactured in Taiwan and are distributed in the US by XS Scuba. The Thermo Pro DIN/K valve has been independently tested as meeting the CGA V9-2009 Compressed Gas Association Standard for Compressed Gas Cylinder Valves. The Thermo valves have a polished heavy chrome cosmetic finish and include a pre-installed DIN-to-Yoke adapter.
DGX Premium SCUBA valves are also manufactured in Taiwan. DGX Premium valves are available in an exceptionally wide variety of specialized versions. The DGX Premium valves have a satin chrome cosmetic finish. Our unbranded generic valves have a lower retail price as a result of being sourced directly from the manufacturer. Although the DIN-to-Yoke adapter is included with most cylinder and valve packages, when sold individually our DGX brand valves do not include a DIN-to-Yoke adapter. The adapter is always available separately as a low cost accessory.
There are internal differences (for example the bonnet nut seal on the Thermo uses a copper crush washer and the DGX uses an O-ring), but oxygen compatible materials and construction of the valves are similar for both Thermo and DGX. Both are described as Nitrox Ready, although Thermo valves are explicitly labeled "40% MAX OXYGEN PREMIXED" on the valve body. Our long experience with the branded Thermo and generic DGX Premium valves has been both have similar reliability and durability in the field. Regardless of brand, every product we sell is backed by Dive Gear Express 5-star quality customer service.
Probably. All of our replacement Nitrox Ready SCUBA valves have an inlet designed to fit 3/4 NPS cylinder neck threads. This fits nearly all North American market SCUBA cylinders of recent manufacture, but there are some rare exceptions. Fortunately, you can use the cylinder neck stamp to determine the answer for yourself.
Assuming your cylinder was manufactured exclusively for the North American SCUBA market in the last 50 years or less, look at the cylinder neck for markings that begin "DOT". If it reads "DOT-3AL-xxxx", "DOT-3AA-xxxx", or "DOT-Xxxxx-3442" it almost certainly has an imperial 0.750-14 NPSM threaded neck opening, referred to in the trade as 3/4 NPS. SCUBA cylinders recently manufactured for other areas may have the name of their thread form stamped on the neck. If the neck stamp includes "3/4 NPSM" or "0.750-14" then the cylinder also has a 3/4 NPS threaded opening. Our replacement Nitrox Ready SCUBA valves will fit any of these cylinders.
There are some rare exceptions, especially for cylinders with very high service pressures or manufactured before 1970; for more information please read our article SCUBA Valves: Regulator Fittings, 200 vs 300 Bar FAQ and Cylinder Neck Threads.
The inlet and outlet on our oxygen compatible DGX Premium O2 Valves are oxygen clean copper metal alloy (aka raw "brass") which will very quickly exhibit some discoloration and spotting after cleaning that that is not present with electroplated chrome finishes typical of other SCUBA valves. Raw brass that is not coated with some kind of sealer (which would defeat the purpose of the valve) will discolor very rapidly, thus appearing aged or used.
If you consider the cosmetics to be important, and maximum compatibility with pure oxygen is less of a concern, then we recommend choosing our standard Nitrox Ready DGX Premium Valves over the DGX Premium O2 Valves.
All of our standard Nitrox Ready SCUBA valves will work with SCUBA regulators having yoke (aka A-clamp), 200 bar DIN or 300 bar DIN fittings. This is virtually all SCUBA regulators, with the rare exception of oxygen service M26 regulators sold in the European Union. The valves have a DIN outlet that requires an DIN-to-Yoke adapter insert for use with yoke regulators. The small DIN-to-Yoke adapter screws in to the DIN valve outlet and may remain permanently if you wish. Our Thermo brand valves include a pre-installed DIN-to-Yoke adapter at no charge. Our DGX house brand valves do not include the adapter, but a DIN-to-Yoke insert is available separately as a low cost accessory.
For more information please read our article SCUBA Valves: Regulator Fittings, 200 vs 300 Bar FAQ and Cylinder Neck Threads.
We strongly recommend purchasing our valves ONLY for cylinders used in North America and the Caribbean. All cylinders in the United States and Canada have Imperial neck thread forms and the valves have over pressure relief devices (aka "burst disks"). Neck thread forms and over pressure relief device requirements in many other areas of the globe are different than North American standards.
One important caution regarding thread compatibility; outside the United States, particularly in Europe, a widely used SCUBA cylinder neck thread form is M25. The 3/4 NPS (ISO 228) and M25 (BS 3643) threads are very similar but not identical; with the use of excessive force it's possible to mate diving cylinders and valves with these two different forms. However, the mismatched threads eventually separate with dangerously explosive force, often causing injury.
The handwheel shearing off the valve stem upon a right-angle impact is a design safety feature present on nearly all modern SCUBA valves, in order reduce the risk that the flow of gas could be interrupted or gas could be lost. Without even having to drain the tank, it's a simple process to replace the valve stem. This is a simple equipment maintenance task many divers can do themselves. Watch our YouTube video titled Valve Stem Replacement.
Nominal Pipe Size (abbreviated NPS) is a term for American standard pipe sizes widely used in the North American industrial trades, but does not describe specific thread forms. Confusingly, National Pipe Straight (also abbreviated NPS) is the name of a specific type of thread form described in American National Standard Pipe Thread standards. Just to be clear they are not the same, one NPS describes a standard for specific sizes of pipe and the other NPS describes a specific type of screw threads used on the ends of pipe.
Historically, many different screw threads have been used on SCUBA cylinder outlets and valves. Using the national pipe thread standards, the proper technical name of the parallel straight threads commonly used to mate modern SCUBA cylinders and valves for the North American market is 0.750-14 National Pipe Straight Mechanical, typically abbreviated as 0.750-14 NPSM. It is frequently also written as 3/4 NPS or 3/4-14; for the purposes of description with SCUBA cylinder and valve applications the terms may all be considered to reference the same threads: 0.750-14 NPSM has a 60° thread angle, a pitch diameter of 0.9820 to 0.9873 in (24.94 to 25.08 mm), and a thread pitch of 14 threads per inch (1.814 mm). The same thread form is also described in a variety of other standards such as ANSI, ASTM, and ISO but those other standards are very rarely referenced in the North American SCUBA market.
See our article SCUBA Valves for more information.
Because we located in the United States , we do not sell SCUBA cylinder valves with the metric M25 inlet thread form. We only sell SCUBA valves for use with US DOT cylinders, which all have imperial neck thread forms and are required to incorporate an over pressure relief device not found on M25 valves.
One important safety caution regarding thread compatibility: The 3/4 NPS (ISO 228) threads most commonly seen on SCUBA cylinders in the US and M25 (BS 3643) threads most commonly seen outside the US (particularly European Union) are very similar but not identical; with the use of excessive force it's possible to mate diving cylinders and valves with these two different forms. However, the mismatched threads eventually separate with dangerously explosive force, often causing injury.
No compatibility testing has been performed by the different manufacturers and neither Dive Gear Express, Dive Rite, nor XS Scuba (who also supplies the Thermo brand) recommend mixing components from different brands of valve modules. However, our customers tell us these valves have similar modular port threads and we have no reports of problems with crossbars, H-adapters and port plugs in that regard. The DIN-to-yoke adapter inserts along with the standard knobs, but not the Vindicator or XS Safety knobs, should be interchangeable without issues. Beyond cosmetics, we can also say for certain that some other internal parts of all four brands do have slight differences and are not interchangeable.