Having a twinset nightmare! Valve Thread woe!

[Dave Bevan]

Hi guys,

I'm trying to build a twinset but I'm having a nightmare. I live in Saudi Arabia and I recently purchased two luxfer AL80 tanks.

I went to purchase the valves and manifold from the UK (I normally get stuff imported) but the dive shop have said that they don't have the correct valves for my tanks they only have M25.

How can I tell what thread is fitted to my tank? I checked the manufacturer's technical details and it says 0.750-14 NPSM, M25 2.0

Now I assume this means both types are available.

How can I tell which mine is?

Dave

 

[tbone1004]

I believe that the m25 tanks are marked with m25x2 on the tank necks. Only way to really tell is going to be going to whichever shop you purchased them from and ask. They should have all of the documentation for those cylinders

 

[Dave Bevan]

Ok I'll have a look at the necks tonight to confirm.

Thanks.

 

[Bob DBF]

If there are not markings, find a machinist or good mechanic and they should have a set of thread gauges. Since it is either one thread or the other, either the metric or American gauge set will tell the story.


Bob

 

[lowviz]

Cut a piece of paper, run water over it, pat off the excess water. Press it into the neck threads. Put it somewhere to dry.

Measure the ridges. If your tank is 14 tpi then an inch ruler will line up exactly with the ridges on both the half-inch and inch marks. You will count seven threads.

 

[Dizzi Lizzi]

^ too easy.

 

[lowviz]

Oh, sorry, nevermind.

I forgot that this is SB, we'll never get to 50 posts this way.

 

[scubafanatic]

Oh, sorry, nevermind.

I forgot that this is SB, we'll never get to 50 posts this way.

Let me help. Can you use that technique to measure the tank threads of a 'Spare-Air' ? ...assuming a 'Spare-Air' is a good idea ?

 

[Peter69_56]

look on the side of the tank and see what standard they have been built to.
DOT-3AL / TC-3ALM / ISO7866

If DOT then it should be 3/4 NPT 14
If ISO7866 then it should be M25

Make sure as M25 fits 3/4 NPT until you pump it to about 100 BAR then they part company

I had same issue when I got my tanks as they sent me an M25 lucky I checked

On my faber tank it states the thread as 3/4 NPT 14