O ring visible between cylinder and valve.

[Agro]

I have checked that before. Tank is M25 same as valve.

You could have said befor.

By the way your o-ring 25x3.5 is wrong, must be 25x3.55. OK, I do not expect this to be any problem at all, 5/100 is very small difference and probably within tolerance. Nevertheless it is not according to the standards.

I hope it is 90 shore, not 70 shore.

 

[happy-diver]

Yeah those STEEL TANKS WITH A SQUARE SEAL can be quite problematic, think Mediterranean flat bread

STEEL TANKS WITHOUT THE SEALING TAPER


Not that Mediterranean flat bread is, but it is.

 

[insomnia]

You could have said befor.

By the way your o-ring 25x3.5 is wrong, must be 25x3.55. OK, I do not expect this to be any problem at all, 5/100 is very small difference and probably within tolerance. Nevertheless it is not according to the standards.

I hope it is 90 shore, not 70 shore.

I found that exact size is 24,99 x 3,53 mm, but you are right that precise size is 25x3.55mm. Shore 90 is recommended for sure. I was told 70 can be OK too, but not ideal.

 

[Agro]

I found that exact size is 24,99 x 3,53 mm, but you are right that precise size is 25x3.55mm. Shore 90 is recommended for sure. I was told 70 can be OK too, but not ideal.

You find 24.99 or 25.00, I guess it is a rounding error.
Never heard about 3.53, only 3.55. I do not know where these 2 numbers are comming from. Anyway it does not matter for this application.
No 70 shore can not be OK for 200/300 bar. Only 90 shore is OK. 70 shore will work for a few days, perhaps month, perhaps years, you do not known. It is far to flexibel and will move around in the groove if pressure increases and decreases, this will wear out the o-ring. It might(!) work for years, it might get dammaged early. It is wrong. Have a look at the o-ring producer's recommendations: 70 shore up to 80 bar, 90 shore for higher pressure.

But anyway your problem seems to be fixed.

 

[insomnia]

You find 24.99 or 25.00, I guess it is a rounding error.
Never heard about 3.53, only 3.55. I do not know where these 2 numbers are comming from. Anyway it does not matter for this application.
No 70 shore can not be OK for 200/300 bar. Only 90 shore is OK. 70 shore will work for a few days, perhaps month, perhaps years, you do not known. It is far to flexibel and will move around in the groove if pressure increases and decreases, this will wear out the o-ring. It might(!) work for years, it might get dammaged early. It is wrong. Have a look at the o-ring producer's recommendations: 70 shore up to 80 bar, 90 shore for higher pressure.

But anyway your problem seems to be fixed.

Yep, the problem is fixed. Thanks for sharing your experience.

 

[Tanks A Lot]

3.53 x 24.99 is a standard BS1806-214 or AS568-214, a very common O-ring indeed.

3.55 x 25.00 is a C0250 as described in ISO3601 or JISB2401. It is also described in DIN3771 and NFT47-501. In SCUBA this is less frequently used than the 214 variant.

Both will work just fine.

What you have in front of you is a EN144-1 connection. The standard calls for an O-ring with the dimension of 3.53mm (+-0.1mm) x 24.99mm (+-0.25mm) in 90 Shore A. From this it is clear that the standard aims squarely at a BS1806-214. The EN144-1 cylinder groove has a recess depth of 2.7mm to 3.2mm, meaning that any O-ring falling within the called for specifications will stand proud. This overfill condition is specifically acknowledged in the standard. This slight overfill puts the initial load onto the O-ring, which helps sealing at low pressures. However, as you found out yourself, this does not lead to a gap.

While it is true that generally speaking the higher pressures call for a higher hardness, there are exceptions to this rule. For example, the DIN477-6 cylinder valve (also an M25x2) specifically called for a 2.65mm x 25.00mm O-ring in 70+-5 Shore A.

 

[Agro]

3.53 x 24.99 is a standard BS1806-214 or AS568-214, a very common O-ring indeed.

3.55 x 25.00 is a C0250 as described in ISO3601 or JISB2401. It is also described in DIN3771 and NFT47-501. In SCUBA this is less frequently used than the 214 variant.

Both will work just fine.

What you have in front of you is a EN144-1 connection. The standard calls for an O-ring with the dimension of 3.53mm (+-0.1mm) x 24.99mm (+-0.25mm) in 90 Shore A. From this it is clear that the standard aims squarely at a BS1806-214. The EN144-1 cylinder groove has a recess depth of 2.7mm to 3.2mm, meaning that any O-ring falling within the called for specifications will stand proud. This overfill condition is specifically acknowledged in the standard. This slight overfill puts the initial load onto the O-ring, which helps sealing at low pressures. However, as you found out yourself, this does not lead to a gap.

While it is true that generally speaking the higher pressures call for a higher hardness, there are exceptions to this rule. For example, the DIN477-6 cylinder valve (also an M25x2) specifically called for a 2.65mm x 25.00mm O-ring in 70+-5 Shore A.

Now I am confused. I thought the DIN 477-6 is a thread which you find at valve's outlet, not between valve and cylinder. Am I wrong?

And I tought sealing is not an o-ring but a fiber disc.

Very confused....

 

[Tanks A Lot]

Now I am confused. I thought the DIN 477-6 is a thread which you find at valve's outlet, not between valve and cylinder. Am I wrong?

DIN 477-6 describes a M25x2 threaded connection between a cylinder valve and the cylinder. It has a 70° taper at the O-ring groove. The standard was retired a fair while ago, but cylinders as well as valves according to this standard are still abundant.

What you are thinking of is DIN477-1 connector #6. This is the W21.8 x 1/14" threaded connection (55° Whitworth) between an O2 cylinder valve and the regulator, which gets sealed via gasket in the standards (looooots of manufacturers ignore this and use an O-ring).