New manifold with centre valve outlet

[spirou]

Hello,

I made research to find a Centre valve outlet, or a  complete manifold with a centre valve outlet and I find this in England.

Screenshot_2024-05-23-20-27-20-434 by Patrick Michel, sur Flickr


Screenshot_2024-05-23-20-40-31-188 by Patrick Michel, sur Flickr

I see that there are thread tank 25x2, ... About 3/4 ...I don't know.


Cheer's 
Fred

[luis]

Hi Fred,

Be very careful not to mix the wrong tank valve threads.


www.divegearexpress.com/gas-tanks/valves

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) imperial threads and M25 (BS 3643) metric 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.

www.hse.gov.uk/diving/cylinder-threads.htm

Mismatching valve threads


There have been several incidents where the threads of diving cylinder valves have failed during charging. This has resulted in the valve being discharged from the cylinder with considerable force, often causing injury.

These failures are often caused by the valve and cylinder having incompatible thread forms. The force exerted at the base of the valve of an 'average' SCUBA cylinder is in the order of several thousand kilograms. Significant injury can be inflicted by a valve that is discharged from a cylinder with this magnitude of force.

Although there are other types, threads are commonly made to two different standards: BS 3643 (25-mm parallel thread) and ISO 228 (G3/4-inch parallel thread). As can be seen in the photo, the two types of thread appear similar. Unfortunately, it is possible for a 25-mm threaded valve to be inserted into a G3/4-inch threaded cylinder neck.

Mismatched threads will often survive several fills before failing

When being fitted, parallel threaded valves should screw in smoothly without binding or feeling loose. However, a 25-mm valve stem, when inserted into a G3/4 inch cylinder neck, will feel very loose until the valve is screwed in about halfway. At this point the threads begin to bind and excessive force is then required to fully screw the valve home. To the inexperienced person, the resulting connection would appear robust.

Specialist thread gauges should be used to check that threads on valves and cylinder necks are compatible. It is also important that the valves are tightened to the torque specified in the applicable standards or the manufacturer's instructions. Too little torque can lead to the valve working loose, whereas excessive torque damages the threads and weakens the integrity of the connection.

Valves should not be fitted, or re-fitted, into diving cylinders without confirmation by a competent person that the threads of both the valve stem and the cylinder neck are undamaged, within their tolerances, and are compatible. Valves should then be fitted using the correct tools to the correct torque value.

[spirou]

May 24, 2024 4:52:48 GMT -8 luis said:

Hi Fred,

Be very careful not to mix the wrong tank valve threads.


www.divegearexpress.com/gas-tanks/valves

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) imperial threads and M25 (BS 3643) metric 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.

www.hse.gov.uk/diving/cylinder-threads.htm

Mismatching valve threads


There have been several incidents where the threads of diving cylinder valves have failed during charging. This has resulted in the valve being discharged from the cylinder with considerable force, often causing injury.

These failures are often caused by the valve and cylinder having incompatible thread forms. The force exerted at the base of the valve of an 'average' SCUBA cylinder is in the order of several thousand kilograms. Significant injury can be inflicted by a valve that is discharged from a cylinder with this magnitude of force.

Although there are other types, threads are commonly made to two different standards: BS 3643 (25-mm parallel thread) and ISO 228 (G3/4-inch parallel thread). As can be seen in the photo, the two types of thread appear similar. Unfortunately, it is possible for a 25-mm threaded valve to be inserted into a G3/4-inch threaded cylinder neck.

Mismatched threads will often survive several fills before failing

When being fitted, parallel threaded valves should screw in smoothly without binding or feeling loose. However, a 25-mm valve stem, when inserted into a G3/4 inch cylinder neck, will feel very loose until the valve is screwed in about halfway. At this point the threads begin to bind and excessive force is then required to fully screw the valve home. To the inexperienced person, the resulting connection would appear robust.

Specialist thread gauges should be used to check that threads on valves and cylinder necks are compatible. It is also important that the valves are tightened to the torque specified in the applicable standards or the manufacturer's instructions. Too little torque can lead to the valve working loose, whereas excessive torque damages the threads and weakens the integrity of the connection.

Valves should not be fitted, or re-fitted, into diving cylinders without confirmation by a competent person that the threads of both the valve stem and the cylinder neck are undamaged, within their tolerances, and are compatible. Valves should then be fitted using the correct tools to the correct torque value.

Hello Luis 

I am happy to read you.

I knew the problems, I have several valve, Spiro , scubapro, beuchat, sos....they are identified, and the tank also. 
But for example la spirotechnique produced during 60's to middle 80's  25x2 SI,  after the standard changed 25x2 ISO that become the standard thread here. I don't know in USA. 

SI and Iso Are very close, question of tolerance, and also with SI the peak of the thread is a bit cut

To your country , USA I know that you use 3/4 NPSM, during long time, but is it still use with new tank?
And in Europe there also an 3/4 imperial 🥳.
So I agree, I must be very careful, but I have test tank 3/4 and M25x2 iso that I used to identified, and if not possible, I asked to specialist in hydro centre.


Finally question for you, I look lots of documents, but the torque, is very variable, for example , Aqualung in 90's give 5kgm, and begin 2000's.  7kgm

La spirotechnique in 80's. 5kgm.     US divers for rigid manifold, docs. +-30 FtPb, that make 4.15kgm, metal sub 3/4NPSM docs give 50 FtPb (6.9Kgm)
  
I just reassemble my twin in 3/4NPSM beuchat manifold I torque a little 5kgm 

So Luis   my I ask to you , which torque you use, when you screw the valve. In the tank thread. (Other advise are also WELCOME 🤗)

Respectfully 
Fred

[luis]

Hi Fred,

The first question is easy. Yes, our standard scuba valve thread in the US is the 3/4 NPS (ISO 228) imperial threads. This thread standard is used in all modern standard scuba cylinder, both aluminum and steel cylinders.


About the torque, of all the mechanical threaded joints I have worked on, the actual torque value in this situation is probably one of the least critical. That is, as long as there is good visible metal to metal contact, between the valve and the tank, around the entire perimeter. That is what keeps the O-ring from extruding.

The metal-to-metal contact is extremely important and that is what you need to look for.

The amount of torque applied, should not affect this, at least not with the corner O-ring seal in the US 3/4” NPSM connection.

The European 25x2 connection appears to use a face O-ring seal (with an O-ring groove under the valve) and may require a bit of torque to compress the O-ring.

Any excess torque doesn’t really accomplish much. Once the tank is pressurized the valve will not twist off and the fear of it twisting off at very low pressure is extremely unlikely even with the lowest toque setting you mentioned.

Again, the most important is to make sure there is no gap between the valve and the tank to avoid O-ring extrusion.

The actual torque value, just pick any of them or just make it tight (with a good size wrench).

Good luck.


BTW, I find it interesting that you all are using kilogram*meters, instead of Newton*meters.

Don't get me wrong, we are still using Foot*pounds and inch*pounds. And of course those are pounds of force, not mass.

[cg43]

Hello Luis

BTW, I find it interesting that you all are using kilogram*meters, instead of Newton*meters. :)



Don't get me wrong, we are still using Foot*pounds and inch*pounds. And of course those are pounds of force,
not mass .



As you anticipate    kg*m is used the same way as  Foot*pounds .

Sure it is wrong  , the right  spelling is kp*m , or kilopond * m  =  kg*m/sec^2 
In every serious book you will find kp*m . 


I grew up with meter/kilogramm/sec. and i'm used to calculate in meter/kilogramm/sec. 
But as Mr. Newton became my hero it was to late for my muscel feeling to work in newton .
If i had to imagine how strong I had to püll on a wrench i  made the  Nm/10  conversion 
(or better approximation) in kp*m and use the force to lift up the same number kg as number kp .
If you are used  pounds and feet your imagination should work with Foot*pounds .

Greetings   Rainer

[spirou]

May 24, 2024 4:52:48 GMT -8 luis said:

Hi Fred,

Be very careful not to mix the wrong tank valve threads.


www.divegearexpress.com/gas-tanks/valves

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) imperial threads and M25 (BS 3643) metric 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.

www.hse.gov.uk/diving/cylinder-threads.htm

Mismatching valve threads


There have been several incidents where the threads of diving cylinder valves have failed during charging. This has resulted in the valve being discharged from the cylinder with considerable force, often causing injury.

These failures are often caused by the valve and cylinder having incompatible thread forms. The force exerted at the base of the valve of an 'average' SCUBA cylinder is in the order of several thousand kilograms. Significant injury can be inflicted by a valve that is discharged from a cylinder with this magnitude of force.

Although there are other types, threads are commonly made to two different standards: BS 3643 (25-mm parallel thread) and ISO 228 (G3/4-inch parallel thread). As can be seen in the photo, the two types of thread appear similar. Unfortunately, it is possible for a 25-mm threaded valve to be inserted into a G3/4-inch threaded cylinder neck.

Mismatched threads will often survive several fills before failing

When being fitted, parallel threaded valves should screw in smoothly without binding or feeling loose. However, a 25-mm valve stem, when inserted into a G3/4 inch cylinder neck, will feel very loose until the valve is screwed in about halfway. At this point the threads begin to bind and excessive force is then required to fully screw the valve home. To the inexperienced person, the resulting connection would appear robust.

Specialist thread gauges should be used to check that threads on valves and cylinder necks are compatible. It is also important that the valves are tightened to the torque specified in the applicable standards or the manufacturer's instructions. Too little torque can lead to the valve working loose, whereas excessive torque damages the threads and weakens the integrity of the connection.

Valves should not be fitted, or re-fitted, into diving cylinders without confirmation by a competent person that the threads of both the valve stem and the cylinder neck are undamaged, within their tolerances, and are compatible. Valves should then be fitted using the correct tools to the correct torque value.

Hello Luis.



I thank you for your response. I now know that I could still buy 3/4 NPSM bottles in the USA, for some of my 3/4 NPSM taps



In fact, all the tightening torques for screwing in the valves are those used in the technical documentation that I could find. I'm used to switching from one to the other, and I also have conversion tables, I use what I find as information, and I calibrate my torque wrenches accordingly. Besides, all my torque wrenches have the three scales, FtPb, Kgm, and Nm.



Maybe you didn't understand my question. In fact I was wondering what tightening torque do you use, when you reassemble the valves, given that in the aqualung documentation for what seems to me to be exactly the same model of valve, I found two different torques once 5 Kgm during the 90s and in the latest version 7 Kgm in the 2000s. The spirotechnics gave 5 Kgm in all the documents that I found on their valve from the 70s until the 90s, for the 3/4 and the 25x2.



In fact it is confusing from one manufacturer to another, the tightening torques are different for identical threads.



Respectfully



Fred

[spirou]

Screenshot_2024-05-25-20-36-58-183~2 by Patrick Michel, sur Flickr
 In the link give by Luis
Screenshot_2024-05-25-20-52-26-866~2 by Patrick Michel, sur Flickr
One of mine conversion table.

Cheer's 
Fred

[cg43]

Hallo Fred

The nessesary torque  for preload (200 bar tank pressure) is  about 30 Nm  or  3 kp*m

The max. permissible torque for a thread  M 25x2  in alu is approximately  300 Nm  or 30 kg*m 

This  wide range is easy accessibel without a torque wrench .
With an stiff wrench it's easy to feel the point the O ring starts its deformation
and the point when the metal surfaces made contact . Afterwards the valve had to be firm .

Greetings   Rainer

 

[spirou]

May 25, 2024 15:12:24 GMT -8 cg43 said:

Hallo Fred

The nessesary torque  for preload (200 bar tank pressure) is  about 30 Nm  or  3 kp*m

The max. permissible torque for a thread  M 25x2  in alu is approximately  300 Nm  or 30 kg*m 

This  wide range is easy accessibel without a torque wrench .
With an stiff wrench it's easy to feel the point the O ring starts its deformation
and the point when the metal surfaces made contact . Afterwards the valve had to be firm .

Greetings   Rainer

 

Hello Rainer 

Thanks for these technical information.

I was surprised by the big difference between the torques that I could read in the technical documentation of the producers.

So now I know the minimum, and the max permissible , and the range is very large. 

Respectfully 

Fred