O2 cylinder pressure

[FishNBarrel]

As a newly certified CCR diver, I have had different dive shops fill my bottles. Some shops fill my 3Ls to close to the 3442 psi rated pressure, while some stop well below that at around 2500 psi. Is there a reason to not fill O2 to the rated pressure of the cylinder?

 

[Superlyte27]

Yes.

 

[fsardone]

Yes.

 

[northernone]

Yes.

This?

 

[fsardone]

As a newly certified CCR diver, I have had different dive shops fill my bottles. Some shops fill my 3Ls to close to the 3442 psi rated pressure, while some stop well below that at around 2500 psi. Is there a reason to not fill O2 to the rated pressure of the cylinder?

There are many (lack of equipment like a booster, hence use of a cascading set of bottles to transfill is one).
But the real and important one it is dangerous to compress oxygen you have 2 of 3 sides of the fire triangle heat from compression and oxygen (high pressure pure oxygen). Actually you have all three of the sides because everything burns with enough oxygen and enough heath.

 

[broncobowsher]

The shops filling close to rated pressure have a booster.

The shops only filling to 2500 are only transfilling from O2 bottles from a gas supplier. There fullest bottle is only 2500 so when they equalize that is what you have. Those big bottles of O2 are shipped with only 2500 in them.

 

[DA Aquamaster]

O2 normally arrived in a high pressure cylinder filled to around 2500 psi. If the shop is transfilling into your tank that's the maximum pressure they can achieve, and they are probably cascade filling off 2 or 3 bottles to keep the pressure in the "high" bottle as high as possible.

Other shops will have a booster and can fill to higher pressures. That said, some shops just won't fill past 3,000 psi even when it is rate to a 3,442 psi service pressure.

----

One of the recommendations when boosting O2 is not to boost more than 4 times it's original pressure if the shop has a single stage booster. At 3,000 psi, that means the supply pressure should be at least 750 psi. At 3500 psi the minimum supply pressure would be 875 psi. If the supply pressures are lower than those numbers, the shop would have to boost into an intermediate pressure tank.

Once I have a K bottle that falls below 750 psi, the remaining contents either get used for partial pressure or continuous blending nitrox, or get boosted into a second partially full O2 supply K bottle. If the destination bottle is down around 1,200 psi I can run my low bottle down to about 300 psi, and at 300 psi I've got my money's worth out of the bottle.

-----

You may find that you want to get your own booster.

Locally we were not able to get anything other than a 2500ish psi transfill, and then only when the shop a) had O2, and b) had a full O2 bottle. They normally ordered O2 on Friday and received it on Monday, but we found that more often than not during the off season they would not order O2.

I gave up and started looking for a used booster. In the interim I had four AL 80s filled to 3000 psi in cave country and then used them as cascade tanks to get us decent fills in between our trips to cave country. I still keep them full and will use two of them to transfill O2 into our 2L O2 tanks during our cave diving trips.

I found a single stage Haskel AG-30 for $500, and invested another $300 in it for new seal kits, then rebuilt it and O2 cleaned it myself. The fill whip plumbing required another $300 in parts that I again cleaned and assembled myself. I also found two K bottles with 2800 psi of O2 in them for $125 each. So the total cost to get up and running was about $1,350, not counting a shop compressor, condenser, moisture separator and filter to drive the Haskel.

That however is still a really good deal compared to $3000 for a rebuilt O2 cleaned AG-30 or $4000 for a new one, plus the cost of the connection hardware and fill whips, which can run around $800 pre made.

If you are in a hurry, and/or are not a do it yourselfer, you can get a portable mini booster for around $2300(plus whips) and they work well for 2L and 3L rebreather bottles.

 

[TrimixToo]

O2 normally arrived in a high pressure cylinder filled to around 2500 psi. If the shop is transfilling into your tank that's the maximum pressure they can achieve, and they are probably cascade filling off 2 or 3 bottles to keep the pressure in the "high" bottle as high as possible.

Other shops will have a booster and can fill to higher pressures. That said, some shops just won't fill past 3,000 psi even when it is rate to a 3,442 psi service pressure.

----

One of the recommendations when boosting O2 is not to boost more than 4 times it's original pressure if the shop has a single stage booster. At 3,000 psi, that means the supply pressure should be at least 750 psi. At 3500 psi the minimum supply pressure would be 875 psi. If the supply pressures are lower than those numbers, the shop would have to boost into an intermediate pressure tank.

Once I have a K bottle that falls below 750 psi, the remaining contents either get used for partial pressure or continuous blending nitrox, or get boosted into a second partially full O2 supply K bottle. If the destination bottle is down around 1,200 psi I can run my low bottle down to about 300 psi, and at 300 psi I've got my money's worth out of the bottle.

-----

You may find that you want to get your own booster.

Locally we were not able to get anything other than a 2500ish psi transfill, and then only when the shop a) had O2, and b) had a full O2 bottle. They normally ordered O2 on Friday and received it on Monday, but we found that more often than not during the off season they would not order O2.

I gave up and started looking for a used booster. In the interim I had four AL 80s filled to 3000 psi in cave country and then used them as cascade tanks to get us decent fills in between our trips to cave country. I still keep them full and will use two of them to transfill O2 into our 2L O2 tanks during our cave diving trips.

I found a single stage Haskel AG-30 for $500, and invested another $300 in it for new seal kits, then rebuilt it and O2 cleaned it myself. The fill whip plumbing required another $300 in parts that I again cleaned and assembled myself. I also found two K bottles with 2800 psi of O2 in them for $125 each. So the total cost to get up and running was about $1,350, not counting a shop compressor, condenser, moisture separator and filter to drive the Haskel.

That however is still a really good deal compared to $3000 for a rebuilt O2 cleaned AG-30 or $4000 for a new one, plus the cost of the connection hardware and fill whips, which can run around $800 pre made.

If you are in a hurry, and/or are not a do it yourselfer, you can get a portable mini booster for around $2300(plus whips) and they work well for 2L and 3L rebreather bottles. View attachment 485263

I had to go out to the garage to make sure you hadn't stolen my AG30 and the collapsible table I use. Your setup is near-identical to mine! You paid a lot less for it, though, since I couldn't find a used booster at the time I bought one.

 

[joshk]

One of the recommendations when boosting O2 is not to boost more than 4 times it's original pressure if the shop has a single stage booster.

What is this recommendation based off of?

 

[Aquanomad]

Interested to know the reasoning on the 4:1 ratio as well. I just picked up a Drager electric booster that is set to 4:1 with a lp supply cut off and hp shut off to keep it at a 4:1. And Im sure the Germans had a reason for it. Drager tends to over engineer everything.