Non scuba valves...

[Externet]

Please move if improper here. Came to this forum section as am unsure where to find experts in threads and valves. Sorry.

There is a CGA870 valve used with oxygen cylinders.
What is the difference between these two ? :

- OXYGEN CYLINDER VALVE - CGA 870
- https://www.amazon.com/Sherwood-Medical-Pressure-Relief-Device/dp/B00PZHZE5E
(shown as 1/2" - 14 NGT)

and

- Airgas
- https://www.amazon.com/Sherwood-Medical-Control-Device-Pressure/dp/B00PZIJPOO
(shown as 3/4" - 16 UNF)

Does it mean there is two kinds of CGA870 valves ?

 

[WarrenZ]

Looks to be two different tank thread types what is your tank threaded as?

 

[CuriousRambler]

Does it mean there is two kinds of CGA870 valves ?

No. CGA870 is the pin index portion of the valve - the one your oxygen regulator will connect to. Another way to put that is to say a medical oxygen tank has only a CGA870 connection. These are not threaded, they use two specifically located pins with a sealing ring (essentially a special oring), and you use a quasi-Yoke-style clamping connector - a la medical oxygen regulator.

The difference on the two you listed is the thread on the other end of the CGA870.

1/2-14NGT means 1/2" diameter threads, 14 threads per inch, NGT is National Gas Taper. NGT specifies how much taper there is to the thread and the interference between male and female threads. I believe (could easily be mistaken) the taper is the same as NPT (National Pipe Thread - what you see on PVC at Home Depot) and fittings will technically mate, but NGT has more interference between male/female components to ensure a better seal.

3/4-16UNF is 3/4" diameter, 16 threads per inch, UNF is Unified National Fine. Again, UNF just specifies the nitty gritty details of how to manufacture that thread - included angle, min/max diameters for female/male threads, root diameters, etc. UNF are straight (non-tapered) threads.

Basically, you have to match the thread to whatever tank or fitting you're trying to adapt to CGA870.

On the above picture, everything above the black oring is a CGA870 connection. Everything below that black oring is 3/4-16UNF thread.

Everything above that oring is identical between the two parts you posted. The threaded section below is the only difference.

 

[Externet]

Excellent explanation, thanks, Rambler.
So T in NGT is for Taper, and T in NPT is for Thread. Interesting.

Same for CGA850 valves; as long as fits the 'A' first stage yoke; can have the old 1/2" from the sixties or the newer 3/4" in aluminium cylinders, tapered or not. Hope am guessing fine there.

 

[CuriousRambler]

I'm not familiar with CGA850 off hand, is that the standard scuba yoke designation?

Taper and thread specs get confusing really quickly. There are a LOT of thread standards around the world. Some of them are identical threads called by different specifications by different industries or countries. Pipe thread is a good example, 3/4 pipe thread is 3/4 diameter - but it's pipe diameter, where pipe is measured on the inside diameter, so a 3/4 pipe thread will actually be just over 1" outside diameter.

I'm honestly not very well versed in CGA (Compressed Gas Association, if that wasn't already known) connections, so I could be wrong on this, but every one of the very few CGA<XXX> connections I'm familiar with are a bit more involved than "just" threads. The CGA designation essentially encompasses the entire connection between a supply source and a "fixture" like a regulator. A CGA designation may involve several types of thread, and those can be different standards on different parts of the CGA assembly. An example would be a CGA580 high pressure gas fitting you might find on a helium bulk tank. There's a captured nut that's threaded 0.960-14NGO. I just looked that up, no way would I know that off hand. I've also never even heard of NGO thread, so I have no clue what that is haha. Searching deeper, that's National Gas Outlet. That nut is captured on a stem/nipple that uses 1/4 NPT. The entire assembly, including the profile of the nipple, is designated CGA580.

For another layer of confusion, you'll sometimes see pipe thread referred to as 1/4MIP or 1/4FIP, standing for Male Iron Pipe or Female Iron Pipe, respectively. Same thing as NPT, just another name. Similarly, you may see MNPT or MPT for a male pipe thread. And to your point, some folks even refer to NPT as National Pipe Taper, not Thread.

It's incredibly easy to get lost in the weeds on this stuff. Unless you're turning your own parts on a lathe, you *rarely* need to know any more than "make sure part A matches part B."

Edit: I'm not sure I'm reading the last part of your post right. Assuming CGA850 is a scuba yoke, then yeah - same thing on the top, but may be straight or tapered thread on the bottom, and may be larger or smaller diameter depending on the tank. What's critical is to know YOUR tank uses 3/4" NPT threads, you use a valve with the exact same threads. Even if the diameter and pitch match, a straight thread and a tapered thread should never be connected together, *especially* in high pressure applications.

 

[WarrenZ]

CGA870 is a medical O2 valve not a scuba valve. As far as I know CGA has nothing to specify SCUBA Valves.

Edited typo.

 

[CuriousRambler]

CGA850 is a medical O2 valve not a scuba valve. As far as I know CGA has nothing to specify SCUBA Valves.

CGA870 is a pin index medical O2 valve. I can't find anything online referring to CGA850. Can you point me to an example? As my name says, I'm curious to learn.

 

[WarrenZ]

CGA870 is a pin index medical O2 valve. I can't find anything online referring to CGA850. Can you point me to an example? As my name says, I'm curious to learn.

Sorry I misremembered the number you are correct I meant CGA870 I will fix above.

 

[Externet]

----> http://www.divediy.com/PIC/PIC/2018891323120.pdf

----> SCUBA Valve Adaptor - August Industries Inc.

----> Metal Diving Tank Accessories , Outlet Cga850 Yoke Inflatable Head With Bleed Valve

----> cga850 at DuckDuckGo

By some reason, cannot scroll to a single page, had to take several ugly matching screen pictures :

 

[CuriousRambler]

Interesting, thanks Externet. Wasn't aware of that.

Similarly interesting, I searched CGA850 with DuckDuckGo before asking and got literally zero relevant results haha.