H valve dilema

[Zef]

I am looking to convert the valve on my tank from a standard valve to an H-valve. I was given an old Scubapro H-valve this evening to try but it would not thread all the way in. I measured the thread pitch at 2mm and the valve is marked M25, so M25x2mm.

The valve that was in the tank measured has a thread pitch of 1.75mm.

The tank in question is a Faber steel 200bar 12L.

I am not familiar with 1.75mm thread pitch tanks/valves.

There is a mark on the crown: G 3/4".....does this refer to the threading?

Can anyone recommend an H or Y valve for this tank?

Thanks,

-Z

 

[tmassey]

Maybe this?

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.

Ref: SCUBA Valves | Dive Gear Express®

 

[runsongas]

G 3/4 is British Standard Pipe Parallel 3/4 (BSPP)

you need a different valve

 

[Zef]

Just found a thread pitch comversion formula

3/4 BSP has 14tpi.

14tpi is approximately 1.8mm...my thread pitch gauge does not have a 1.8mm gauge but 1.75mm fit near perfect...I guess that would be roughly 1.8mm.

-Z

 

[Zef]

G 3/4 is British Standard Pipe Parallel 3/4 (BSPP)

you need a different valve

Thanks appreciate the help...I was researching and typing the same time you were...just was not sure what the G meant until I read your post...I made the assumption the 3/4" was referring to BSP.

Cheers,
-Z

 

[rhwestfall]

3/4 -14 is the standard here in the US......

 

[Zef]

3/4 -14 is the standard here in the US......

Is the thread angle in the US 60 or 55 degrees?

BSPP seems to be 55 degrees.

Does angle matter that much?

-Z

 

[tmassey]

Explanation of common threads including BSP & NPT

The details are here. They are not compatible — certainly not in HP situations!