LDS Filling Nitrox - Partial Pressure Blending

[Jimmer]

Thanks for your 2cents. Now I'd understand. I knew there was a SAFER way. Just not economical.

Sounds like it is a business decision to put O2 first then top off with air. I could just imagine the initial cost plus operation cost of a 02 cleaned compressor capable of pushing 3500psi.

I don't agree with you that topping with O2 would be safer. I think starting with the O2 and topping with the air is safer, AND a better business decision. I'd rather deal with pure O2 at a couple hundred PSI than boosting it to 3000 (or higher in an HP tank). Boosting has the potential to add a lot of heat, which can be a big problem with O2. If you are just transfilling from a storage bottle of O2, into a scuba tank, and the blender knows what he is doing, he will be doing it nice and slow and the possibility of heat build up is lower than with boosting.

 

[do it easy]

I don't agree with you that topping with O2 would be safer. I think starting with the O2 and topping with the air is safer, AND a better business decision. I'd rather deal with pure O2 at a couple hundred PSI than boosting it to 3000 (or higher in an HP tank).

I'm with you on this one- if it's a shop I know, I don't mind standing in the fill room while other blenders I know are working, but as soon as the O2 booster starts, I leave the room.

 

[UaVaj]

I don't agree with you that topping with O2 would be safer. I think starting with the O2 and topping with the air is safer, AND a better business decision. I'd rather deal with pure O2 at a couple hundred PSI than boosting it to 3000 (or higher in an HP tank). Boosting has the potential to add a lot of heat, which can be a big problem with O2. If you are just transfilling from a storage bottle of O2, into a scuba tank, and the blender knows what he is doing, he will be doing it nice and slow and the possibility of heat build up is lower than with boosting.

Good point. Looks like neither way is safer then what it is.

Which is worst? Heat or Mixture?

I think it is safe to say it is a trade offs. Since it is a cheaper setup to go O2 first and top off with air. That is the business decision.

 

[do it easy]

I think that heat is worse- any gas flowing too fast can produce heat, especially if the fill station is poorly designed. Even if it's not pure O2, that heat can cause combustion, which can result in an explosion or contaminated gas (CO/CO2 as the combustion by-products). Anyway you slice it, it can be fatal.

 

[Jimmer]

Good point. Looks like neither way is safer then what it is.

Which is worst? Heat or Mixture? It is a trade offs.

Since it is a cheaper setup to go O2 first and top off with air. That is the business decision.

Heat is worse, simple as that. If the cylinders are cleaned, there is nothing automatically dangerous about having pure O2 in a scuba tank. The danger comes from a dirty tank, a dirty valve, a bad blender with bad technique. Don't forget, aside from membrane separation, you are always dealing with big storage bottles of pure O2. So if it's safe in those storage bottles, why can't it be safe in a properly cared for scuba tank? As for the cheaper to go O2 first. Even if I had a shop with a top of the line booster pump, I'd still go O2 first. It's the better move.

 

[UaVaj]

Heat is worse, simple as that. If the cylinders are cleaned, there is nothing automatically dangerous about having pure O2 in a scuba tank. The danger comes from a dirty tank, a dirty valve, a bad blender with bad technique. Don't forget, aside from membrane separation, you are always dealing with big storage bottles of pure O2. So if it's safe in those storage bottles, why can't it be safe in a properly cared for scuba tank? As for the cheaper to go O2 first. Even if I had a shop with a top of the line booster pump, I'd still go O2 first. It's the better move.

I am begining to understand this.

Since we are talking about 02 cleaned equipment. Let me take this a bit further. Obviously once the inside of the tank is O2 cleaned. As long as it is filled only with hydrocarbon free air and pure oxygen. The inside of the tank will continue to remain clean.

What about the valve? I am refering to the part of the valve that is totaly exposed to the open enviroment. The parts and path where the O ring lies right before the valve shutter. Does the LDS O2 clean that section of the valve every single time and replaces the O ring every time before filling a nitrox tank? I mean what if there was a spec of grease/whatever on the O ring or the path leading into the actual valve shutter. With pure O2 running past that path to get into the cylinder. Wouldn't that be enough contaminants to cause BOOM!!

 

[Jimmer]

I am begining to understand this.

Since we are talking about 02 cleaned equipment. Let me take this a bit further. Obviously once the inside of the tank is O2 cleaned. As long as it is filled only with hydrocarbon free air and pure oxygen. The inside of the tank will continue to remain clean.

What about the valve? I am refering to the part of the valve that is totaly exposed to the open enviroment. The parts and path where the O ring lies right before the valve shutter. Does the LDS O2 clean that section of the valve every single time and replaces the O ring every time before filling a nitrox tank? I mean what if there was a spec of grease/whatever on the O ring or the path leading into the actual valve shutter. With pure O2 running past that path to get into the cylinder. Wouldn't that be enough contaminants to cause BOOM!!

In theory I suppose that could be an issue. Realistically I have never heard of this being an issue. Like other's have said, Oxygen really isn't this crazy gas just looking for a chance to blow stuff up. If it's handled with care and respect, it's pretty safe. As for a spec of grease or something like that, most guys that do fills around here crack the valve quickly before attaching the fill whip. This will blow off water/dust/debris pretty effectively, and away you go. Even if that was an issue, it would still be an issue regardless of whether you go O2 first or Air first.

 

[David P]

yes you should be careful of O2 under pressure, but done forget about all the Tom, Dick, & Harry welders out there that use large O2 bottles every day for cutting. Yeah freak accidents happen, bit ne smart and all should be good

 

[UaVaj]

In theory I suppose that could be an issue. Realistically I have never heard of this being an issue.

As for a spec of grease or something like that, most guys that do fills around here crack the valve quickly before attaching the fill whip. This will blow off water/dust/debris pretty effectively

If cracking the valve quickly before attaching the fill whip to blow off water/dust/debris is pretty effective - qualifies as being O2 cleaned for this section/path of the overall filling system?

What gives? O2 cleaned is more of a gimmick than reality. I am sure I am wrong so hopefully someone will chime in on the real reason.

 

[John_B]

Captain is abolutely right about the fire triangle.

Another way to look at high concentrations of O2 is that it effectively lowers the temperature that other stuff combusts at. Air is approx. 21% O2 , if air was 10% O2 almost nothing would spontaneously combust, if air was 90% O2 all kindsofstuff would spontaneously combust.

So with a high enough O2 percentage under enough pressure and some other conditions and you can basically make anything burn, even metals. Add to the equation the physical act of stuffing extra molecules of a gas into the same sized space is exothermic (e.g. generates heat, back to the captain's triangle). Now add in the nature of hydrocarbons that want to combust at the drop of a hat anyway... You begin to get the picture.

So adding O2 first, under low pressure, very slowly, into tanks cleaned of hydrocarbons, then topping off with 21% air or 32% nitrox, its all designed to make getting whatever mix needed into your tank as safely as possible for the person doing the blending.

HTH

John