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Fibonacci
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What twin manifold is this?!

Wed Dec 14, 2016 6:39 am

This looked like a good buy at only $45... unbranded but solid looking modular J valve twin manifold with convertible DIN/Yoke outlets.

Image

Image

Not much clearance to the Kraken can in standard setup but easily reversed...

Image

So far so good...

Advertised as a 3/4" x 14 NSPT valve on unwrapping it I immediately noticed it seemed more beefy than the valve thread on the vintage 72 cu ft steelie I just replaced.

Checking with a thread gauge it is indeed 14 tpi BUT LH module major diameter is 1.0340" or 26.26mm, RH is 1.0360".
Measuring a known 3/4" x 14 NSPT valve reveals a major diameter of 1.030" vs the nominal major diameter of 1.050".
Aargh...!
I then thought it could be some oddball 26mm Metric thread but no Metric thread gauge comes close... 14tpi gauge fits perfectly and the threads of a known 3/4" NSPT valve fit perfectly when meshed together.

Bonnet nut perfectly fits a 17mm Metric socket but is loose on Imperial.

When separated to check, the end modules seal against the centre module using a flat DIN style o-ring vs the usual vintage metal-to-metal gland nut or the current twin annular o-rings.

I cannot find any reference to a tank this manifold would fit... any clues gratefully received or i have a new paperweight Image
'A man can never have too much red wine, too many books or too much ammunition' Rudyard Kipling

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luis
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Re: What twin manifold is this?!

Wed Dec 14, 2016 7:53 am

Take a look at the information at the bottom of this link:
https://www.divegearexpress.com/library ... ck-threads

Here is some more information:
http://www.hse.gov.uk/diving/cylinder-threads.htm

One important caution regarding thread compatibility; outside the United States, particularly in Europe, a widely used SCUBA cylinder neck thread form is known as 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.

There was a local hydro station that once have accidentally placed an M25 hydro adapter fitting in a 3/4 NPS tank. They caught the mistake before there was any harm done (the hydro pressure could have ruined the threads, but there was very little chance of a catastrophic accident). I looked at it and the threads are just a bit smaller and it fits easy. It didn't feel too loose once there was several thread engagement either because the thread pitch is just a bit off.

Be very careful.
Luis

Buceador con escafandra autónoma clásica.

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Fibonacci
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What twin manifold is this?!

Wed Dec 14, 2016 2:06 pm

Many thanks for the links Luis... yes i am treading very carefully here!
I also found a pipe thread ID link which shows that a 3/4" NSPT actually has a nominal OD of 1.050" x 14 tpi so this manifold is close, but still 0.014" to 0.016" undersize.

http://www.fairburyfastener.com/xdims_pipe_threads.htm

http://atlanticscuba.co.uk/index.php/20 ... t-1-2-2-2/

"Most modern U.K. diving cylinders will have an M25x2 thread. Older U.K. cylinders were imperial ¾” BSP, which was phased out around 1994. Other cylinders threads included tapered threads like the 715. M25 cylinders and valves are marked with M25x2, whereas very few 3/4” valves or cylinders were marked. U.S. Cylinders have an American imperial thread, 3/4” NSPT, a completely different thread from the British 3/4” BSP. "
So could possibly be an older UK fitting 3/4" BSP which is also 14 tpi major diameter is 1.041" much closer to the dimensions of this manifold at 0.005" to 0.007" undersize. This UK heritage may explain the more recent style convertible DIN yoke on a J valve setup but I bought it from the US so a bit of a long shot!
https://www.google.com.au/search?q=3%2F ... dimensions
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Herman
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Re: What twin manifold is this?!

Wed Dec 14, 2016 3:45 pm

I suspect they are British straight pipe thread (BSPT). The major diameter is a max of 1.041 inches so you are about right in diameter. If they are British Pipe thread you can tell if you look very closely (and have a good thread gauge). Imperial and metric threads are 60 degree threads and will fit tightly and completely in a thread gauge. British threads (Whitworth) are 55 degrees, not much difference but if you are looking for it you can see it. The thread gauge does not fit on the threads well, you can see light around them. I know some Faber tanks were made with British straight pipe thread in the 70's, I worked on a friends Technisub Raid that had them.
Herman

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Fibonacci
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Re: What twin manifold is this?!

Wed Dec 14, 2016 5:04 pm

Hmm... yes will measure and check carefully under a jeweller's loupe when I get home from work tonight...

As you say, the two threads are very similar but are not compatible:

WARNING: Never, never try to mate a BSP fitting with an NPT or NPS fitting if the pressure holding capability is at all critical.

NPT/NPS and BSP threads are not compatible due to the differences in their thread forms, and not just the fact that most diametrical sizes have a different pitch. NPT/NPS threads have a 60° included angle and have flattened peaks and valleys (this is a Sellers thread form); BSP threads have a 55° included angle and have rounded peaks and valleys (this is a Whitworth thread form).


http://pipeandhose.com/?q=node%2F2
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Fibonacci
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What twin manifold is this?!

Thu Dec 15, 2016 6:59 am

OK with a jeweller's loupe, both thread gauges and careful lighting you can indeed tell clearly that this thread is not a standard 3/4" x 14 60 deg NSPT thread but is a 3/4" x 14 55 deg BSP straight pipe thread!

So I DO have a new paperweight but at least i learned something... don't buy cheap unbranded vintage SCUBA manifolds without full heritage off people claiming it was an estate sale and they "know nothing about SCUBA valves"... they are cheap for a REASON
'A man can never have too much red wine, too many books or too much ammunition' Rudyard Kipling

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Herman
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Re: What twin manifold is this?!

Thu Dec 15, 2016 7:28 am

It's not a paperweight if you can find tanks to go with it. I know Faber made steel 80's that had BSPT....which is likely what that manifold was made for.
Herman

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Drado
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Re: What twin manifold is this?!

Fri Dec 16, 2016 9:27 am

I once had an old Scubapro tank made by IWKA with M25 threads on them. Sent it in for hydro, and the folks used a standard 3/4" fitting. Held pressure for a while then burette readings went all over the place as a small geyser erupted around the threads (or so I was told). They eventually found the proper fitting and the tank passed hydro.
_______________________________
Ed

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Fibonacci
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Re: What twin manifold is this?!

Mon Dec 19, 2016 12:33 am

Herman wrote:It's not a paperweight if you can find tanks to go with it. I know Faber made steel 80's that had BSPT....which is likely what that manifold was made for.
True, but here in Australia there's a couple more hurdles (apart from having to hydro test all tanks EVERY year!):

From DiveOz
The Oz std is 3/4" NPSM but Sterling in the early days of bringing in Faber cylinders brought in some 3/4" BSP, be warned they almost fit the 3/4" NPSM cylinders.
The Yanks use 3/4" NPSM but the UK and Europe use M25 an/or M18.

You can now get all the above in Oz so be very careful.

Make sure your valve has a burst disc and that the cylinder has been issued with work cover approval if they are not AS1777, i.e. BS5045 etc. if not already hydro stamped are illegal.


Unfortunately what looks like a large hex headed burst disc is actually the reserve mechanism... this manifold has no burst disc :(
'A man can never have too much red wine, too many books or too much ammunition' Rudyard Kipling

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