Yes or No?

[baldeagle]

From what ive been told is that unless you screw a fitting into the din stem of a modern cylinder that pushes into the little recess that is visible at the back of the valve then the cylinder should retain a minimum of 5bar of pressure in it...assuming that this is correct then i fail to see how that any contamination can enter the cylinder unless the hold pressure rises above 5bar

[copperband]

I'm thinking specifically with regard to Red Sea live aboards, I don't have a regular dive buddy and after many trips I think I have had my fair share of 'less than confidence inspiring' buddies.

Therefore thinking of taking my own bit of redundancy with me in the shape of a pony., which I don't belive are available on boats to hire.

Ah, what gas are you proposing to put in it?

[nigelH]

From what ive been told is that unless you screw a fitting into the din stem of a modern cylinder that pushes into the little recess that is visible at the back of the valve then the cylinder should retain a minimum of 5bar of pressure in it...assuming that this is correct then i fail to see how that any contamination can enter the cylinder unless the hold pressure rises above 5bar

And you looked at a cylinder valve and still believe this?

I must sell you something.

[Digger]

OK, the simple reality is that unless they are spilling fuel everywhere (which believe me they are quite careful to avoid with planes) there is very little that is going to invade a cylinder and start uncleaning it.

It will clean as when it went in, and will be absolutely fine to fill with pure O2.

I'd quite happily stick it between my legs and do it. And rather quickly no problems.

O2 clean is frankly, largely a load of tosh. Ever seen those completely empty J cylinders sitting out the back of an engineers workshop? Think they get cleaned and the valve serviced, and some dive shop monkey to kiss it three times? No, they just get filled. Same as dive cylinders.

We should manage the risks so that no-one gets blown up, but it just isn't going to make a difference in this case.

Oh, and if you're off to the Red Sea, they don't care if it's O2 clean anyway, they use membrane systems so there isn't any neat O2 going through the valve, only 30%, which you don't need anything to be O2 clean for really.

Digs.

[baldeagle]

No...listening to a higher authority on these matters...its always possible i may have the wrong type cylinders and valves in mind but something in the back of my mind recalls a recent conversation and discussion...a retentive mind is useful especially with the amount of bollocks that is sometimes flying about on this site

[Frankie Price]

Any filling station, whether pumping air or O2 into a cylinder is always cautious when they receive an opened empty cylinder. This is because they can't tell how long the cylinder has been opened and if the cylinder has had any water , be it salt or fresh, standing in it for any length of time.
When they receive a closed and pressurised cylinder they know that there is every chance it has either had full pressure in it recently or has stood with reduced pressure for some time. In which case the cylinder is less likely to go bang when given a 232 fill.
This is the reasoning behind the empty/opened cylinder debacle and not the O2 clean issue.

[Frankie Price]

As a footnote to my previous post, most filling stations don't care about oil mist deposits in a cylinder when charging them with O2 as usually the oil combusts at relatively low pressure and forms CO in the mix. It would take a hell of a lot of oil inside to explode a cylinder. The only way sufficient oil could get into a cylinder is by having the valve open and storing it in an environment where oil could actually drip through the valve get inside.
(I'm sure my regular buddy could come up with some figures as to how much oil would be needed to cause a bang. )

[Digger]

No...listening to a higher authority on these matters...its always possible i may have the wrong type cylinders and valves in mind but something in the back of my mind recalls a recent conversation and discussion...a retentive mind is useful especially with the amount of bollocks that is sometimes flying about on this site

I think you have the wrong type of valve. But there are no cylinders that sit with 5 bar in them, even when they appear empty. If they appear empty they are.

The only exception to this that I can think of is J valves, which have a lever that unless pulled will hold a reserve, approx 50 bar or so. You can completely empty the cylinder, you get the tightness of running out of gas, and then pull the lever and it gives you a reserve. Useful if you don't have a gauge, but also rather deadly if the lever gets pulled by accident

But there's no way for a DIN valve to hold gas with the valve open.

Digs.

[Redshift]

When I went to a liveaboard in the Red Sea, two people took their rebreathers, cylinders included. No problem in getting them filled and no explosions.

[baldeagle]

Whether it is our diving cylinders or not all i know is that certain cylinders dont completely discharge...i may not have the specifics right but worry not i will find out when i get chance to question the great oracle of cylinder knowledge