A few newbie tank questions

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Firstly, don't buy your own compressor. Its THOUSANDS of dollars down, THOUSANDS in maintenance. Filters, valves, intake, bleeds, air samples... don't. The big big big commercial compressors have better fill rates (cubic ft/min). The giant Mako at our shop is 13 cfm, and boss man puts thousands in it for it to pump clean air, and to be up to standards.

Pay your $10-$15 per air fill. You'll spend less than you would on a compressor.

Anyway:

1. Buy aluminum. They don't rust. That in mind, you have to treat your cylinder well or you'll see aluminum oxide where there is water contact - under your cylinder boot, for example. Rinse it with freshwater, remove the boot with a rubber mallet occasionally.

2. Your weighting is different with steel versus aluminum. I don't recommend LP steel, because these days cylinders are more reliable and fill to a higher pressure.
Get a Luxfer or Catalina aluminum 80, serial number that starts with EA for Luxfer or T for Catalina. These are "neutral" cylinders that fill to 3300 and do not end up positively buoyant at the end of your dives. They are lighter than even LP steel (to carry), and they have great buoyancy characteristics for beginners. Full, they start about 5, pounds negative and end neutral (500psi). Comparatively, "standard" non neutral, 3000psi aluminum 80s start about 1 pound positive and end about 6 pounds positive. Get a 63 aluminum for your son.

3. Never assume a cylinder is ready to go. If you buy online, ask about its "hydro" date. Its hydrostatic requalification. It should have a valid RIN (requalifyer identification number) and the month to the left and the year to the right of that stamp. You can look online for a RIN locator to see if they're legit. never trust your hydro facility until you know you can. As for the visual, the valve should be torqued to 50 ft lbs, use proper lube and a proper o-ring, and be inspected to PSI-PCI standards, as they are the only cylinder inspection training agency recognized by DOT, who regulates high pressure cylinders. High pressure is defined as 29psi or higher, per DOT and CGA.

Buying online from retired divers opens you to the risk of obtaining condemned or horribly damaged cylinders, or the 6351-T6 aluminum alloy, which need an eddy current test because they are prone to sustained load neck cracks. The aluminum 80s of the 6351 alloy were manufactured by Luxfer through January 1988, and Walter Kidde, any year. The Luxfer 63 cbfts were the 6351 alloy until June, 1988. During Hydro, these also must receive a VE test AND stamp next to the year on their hydro stamp.

Bottom line, trust where you get your cylinders from, and trust where you get them inspected. Aluminum 80 neutral, 3300psi, from Luxfer or Catalina would be great for you or your son, but if he needs something smaller, get him an aluminum 63. If you get a 6351, be sure your facility knows what they are doing with their eddy current test.
 
Firstly, don't buy your own compressor. Its THOUSANDS of dollars down, THOUSANDS in maintenance. Filters, valves, intake, bleeds, air samples... don't. The big big big commercial compressors have better fill rates (cubic ft/min). The giant Mako at our shop is 13 cfm, and boss man puts thousands in it for it to pump clean air, and to be up to standards.

Pay your $10-$15 per air fill. You'll spend less than you would on a compressor.

Anyway:

1. Buy aluminum. They don't rust. That in mind, you have to treat your cylinder well or you'll see aluminum oxide where there is water contact - under your cylinder boot, for example. Rinse it with freshwater, remove the boot with a rubber mallet occasionally.

2. Your weighting is different with steel versus aluminum. I don't recommend LP steel, because these days cylinders are more reliable and fill to a higher pressure.
Get a Luxfer or Catalina aluminum 80, serial number that starts with EA for Luxfer or T for Catalina. These are "neutral" cylinders that fill to 3300 and do not end up positively buoyant at the end of your dives. They are lighter than even LP steel (to carry), and they have great buoyancy characteristics for beginners. Full, they start about 5, pounds negative and end neutral (500psi). Comparatively, "standard" non neutral, 3000psi aluminum 80s start about 1 pound positive and end about 6 pounds positive. Get a 63 aluminum for your son.

3. Never assume a cylinder is ready to go. If you buy online, ask about its "hydro" date. Its hydrostatic requalification. It should have a valid RIN (requalifyer identification number) and the month to the left and the year to the right of that stamp. You can look online for a RIN locator to see if they're legit. never trust your hydro facility until you know you can. As for the visual, the valve should be torqued to 50 ft lbs, use proper lube and a proper o-ring, and be inspected to PSI-PCI standards, as they are the only cylinder inspection training agency recognized by DOT, who regulates high pressure cylinders. High pressure is defined as 29psi or higher, per DOT and CGA.

Buying online from retired divers opens you to the risk of obtaining condemned or horribly damaged cylinders, or the 6351-T6 aluminum alloy, which need an eddy current test because they are prone to sustained load neck cracks. The aluminum 80s of the 6351 alloy were manufactured by Luxfer through January 1988, and Walter Kidde, any year. The Luxfer 63 cbfts were the 6351 alloy until June, 1988. During Hydro, these also must receive a VE test AND stamp next to the year on their hydro stamp.

Bottom line, trust where you get your cylinders from, and trust where you get them inspected. Aluminum 80 neutral, 3300psi, from Luxfer or Catalina would be great for you or your son, but if he needs something smaller, get him an aluminum 63. If you get a 6351, be sure your facility knows what they are doing with their eddy current test.

Thanks for the helpful info. I was leaning towards steel before reading it, unaware that aluminum was available with better buoyancy. I see that higher capacity units with good buoyancy are also available, without too much out of water weight penalty. I'm a stocky 5'8", 30" inseam. What negatives to you see with this tank, vs the 80 you recommend?:
"The Luxfer 100 cubic foot (13.2 liter) cylinder is a 3300 psi (227.5 bar) service bottle. The tank is 26.2" (66.6 cm) tall with an 8" (20.3 cm) diameter. The cylinder weighs 41.1 lbs. (18.64 kg) is negative 4.6 lbs. (2 kg) when full in salt water and is negatively buoyant 2.8 lbs. (1.27 kg) when empty. The cylinder comes with a Pro Valve. The Pro Valve is one of the highest flow cylinder valves available today and is also a convertible valve. Whether you dive Yoke or DIN regulators this valve will work for both. Valve has easily removed 200 bar DIN insert to convert the valve for use with DIN regulators. Valve has a heavy duty deign with a smooth operating mechanism and multi-ported burst disc plug for added safety."
Thanks in advance,
Peter
 
Thanks for the helpful info. I was leaning towards steel before reading it, unaware that aluminum was available with better buoyancy. I see that higher capacity units with good buoyancy are also available, without too much out of water weight penalty. I'm a stocky 5'8", 30" inseam. What negatives to you see with this tank, vs the 80 you recommend?:
"The Luxfer 100 cubic foot (13.2 liter) cylinder is a 3300 psi (227.5 bar) service bottle. The tank is 26.2" (66.6 cm) tall with an 8" (20.3 cm) diameter. The cylinder weighs 41.1 lbs. (18.64 kg) is negative 4.6 lbs. (2 kg) when full in salt water and is negatively buoyant 2.8 lbs. (1.27 kg) when empty. The cylinder comes with a Pro Valve. The Pro Valve is one of the highest flow cylinder valves available today and is also a convertible valve. Whether you dive Yoke or DIN regulators this valve will work for both. Valve has easily removed 200 bar DIN insert to convert the valve for use with DIN regulators. Valve has a heavy duty deign with a smooth operating mechanism and multi-ported burst disc plug for added safety."
Thanks in advance,
Peter
There are just a couple of oddities about an AL100 you should know before you buy one and find out later:
  • The diameter is larger. If you are switching back and forth between this and an AL80 or AL63, you will be readjusting your tank band every time. Also, if you are bringing the tank on charters, it might not fit the cylinder brackets around the sides of the boat.
  • When you are out of the water and walking around in your gear, you will be carrying an extra 8-1/2 pounds on your back/shoulders once you have dialed in your correct weighting, versus a standard AL80 with your weighting correct. Extra 9 versus a Neutral 80. (My calculations are for Luxfer, haven't worked them for Catalina) That may or may not matter to you, but for some reason that extra bit just pushes me over into the noticeably annoyed range when I am walking across the lawn at the quarry.
 
There are just a couple of oddities about an AL100 you should know before you buy one and find out later:
  • The diameter is larger. If you are switching back and forth between this and an AL80 or AL63, you will be readjusting your tank band every time. Also, if you are bringing the tank on charters, it might not fit the cylinder brackets around the sides of the boat.
  • When you are out of the water and walking around in your gear, you will be carrying an extra 8-1/2 pounds on your back/shoulders once you have dialed in your correct weighting, versus a standard AL80 with your weighting correct. Extra 9 versus a Neutral 80. (My calculations are for Luxfer, haven't worked them for Catalina) That may or may not matter to you, but for some reason that extra bit just pushes me over into the noticeably annoyed range when I am walking across the lawn at the quarry.
Thanks for the insights, Jack. I noticed the diameter is 8" vs 7.75", but wasn't sure if .25" was enough to keep it from fitting onboard tank racks. I was considering mainly local, freshwater use, since most charters will involve air travel for me, and I'll have to rent tanks. I had thought that I could lose lead vs a 80, but I guess no more than what I could lose with a neutral 80. Realistically, considering I plan to use nitrox, how much more volume would I get with the 100 over the 80? Aren't there some restrictions on Nitrox that don't apply to air?
 
Hmmm.... not sure what you may have heard regarding EAN. Pure O2 is not to be compressed higher than 3000 psi, but I don’t think that has bearing here. I am not a blender, but I think with partial pressure blending you add the O2 first, then the O2 clean air after. In which case there is no issue. If O2 is last then there would be a concern stepping up to 3300.

I did the math, and even if you can only get an AL100 filled to 3000, you will 15-16% more air than an AL80.

And you don’t need to add lead with a 100 versus an 80, but the tank itself is heavier. Which doesn’t matter IN the water...
 
The difference between a 7.25" tank and an 8" tanks is enough to make adjusting cam bands a real pain. AL 100s suck in terms of bulk and weight. HP steel 100s are so much better in terms of buoyancy, dry-land weight, and swapability to rented AL 80s (both are 7.25" tanks). HP 100 steel tanks are more expensive, but their more negative characteristics in water, on-land weight, and overall size make them seriously great tanks.

@Peter McCann, any restrictions you have with nitrox versus air (maximum depth) are completely irrelevant of tank size/material. You can use nitrox with both aluminum and steel tanks. An AL80 holds 77.5 cf at it's rated service pressure. A steel HP 100 holds 100 cf at it's rated service pressure. So an HP 100 gives you 22.5 cf more gas; that's substantial.
 
The difference between a 7.25" tank and an 8" tanks is enough to make adjusting cam bands a real pain. AL 100s suck in terms of bulk and weight. HP steel 100s are so much better in terms of buoyancy, dry-land weight, and swapability to rented AL 80s (both are 7.25" tanks). HP 100 steel tanks are more expensive, but their more negative characteristics in water, on-land weight, and overall size make them seriously great tanks.

@Peter McCann, any restrictions you have with nitrox versus air (maximum depth) are completely irrelevant of tank size/material. You can use nitrox with both aluminum and steel tanks. An AL80 holds 77.5 cf at it's rated service pressure. A steel HP 100 holds 100 cf at it's rated service pressure. So an HP 100 gives you 22.5 cf more gas; that's substantial.
What about service life in steel vs AL, in salt vs fresh as primary environments?
 
As long as you soak the steel tanks in freshwater after being in salt water (remove the boot periodically to ensure you soak the salt out from under the boot) it should last decades. As long as you take care of it, the steel should last as long as the aluminum. The only downside to steels is the higher upfront price.
 
You like galvanized or painted (galvanized +$25)?
I'd rather, hot dipped, galvanized. I have painted over spray on galvanized (Faber LP50s for sidemount) and the paint job is readily scratched off by my harness hardware. Faber tanks bigger than my tiny ones come as, hot dipped, galvanized. I wish the LP50s did. Just a way to make them more bullet proof and easier maintenance for their ocean side life.
 
https://www.shearwater.com/products/teric/

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