K valve threads

[MarinerG23]

does anyone know the thread size on K valves

 

[neil]

The most common is a 3/4 inch NGS thread with 14 TPI. This is what you'll see on most tanks. There's also a 7/8 thread used on HP cylinders, an old obsolete 1/2 straight and a 1/2 tapered pipe thread. This is for US tanks, I'm not familiar with European cylinders.

Neil

 

[Bob3]

The old 1/2" tapered threads were NGT rather than pipe (NPT). Not sure how big the difference is, but don't like to run pipe threads into a scuba tank.
1/2" tapered K valves are still frequently used for bailout (pony) bottles.

 

[neil]

Bob,
Of course you're correct, it's not exactly a 1/2 pipe thread, but it is similar. The NGT thread is basically an NPT thread lenghtened to allow for wear through repeated tightening of the valve.

NPT = American (National) Pipe Thread standard
NGT = National Gas Taper Thread

Neil

 

[MarinerG23]

I thank you both for the extremely useful information

 

[Norm]

All of the old Sherwood brochures called them 3/4" straight pipe threads.

 

[Scubaroo]

Okay then, does anyone know specifically the threadsize on a ScubaPro 95 LP steel tank? I've seen one for sale and would like to buy it, but it has an ancient H valve, which I want to replace with a yoke fitting (without using an adapter). Not sure of the year of manufacture.

Ben

 

[devjr]

Ben, the LP 95 thread is standard 3/4 straight pipe thread(o-ring), same as US aluminum tanks, etc. The only variation for the US market that you need to be aware of is that HP tanks carry a smaller, 7/8-16 machine thread reserved for the DIN valve.

If these sizes seem contradictory, it's because the pipe thread size is defined as the diameter of the INSIDE of the threaded (male) pipe and the machine thread is defined as the OUTSIDE diameter of the pipe.

Never mind, standard yoke valves will fit your tank.