2 questions on steel vs. aluminum

[divindoc]

had an opportunity this past weekend to dive w steel 80s for the first time and I really enjoyed the characteristics of them as opposed to their aluminum counterparts...so the first thing I am curious about is to get some feedback from those more experienced on the advantages and disadvantages of both steel and aluminum...the second question I have is about reserve...I've always been taught as most have to always keep 500 psi in reserve; if diving w/steel 80s, can you lower this in proportion, say keep a reserve of 350 psi?

If you liked the steel 80's try a HP steel 100. I think it trims out much nicer than the 80 (I'm 5'8") for my torso plus you've got 20 more cu.ft. to play with. It's several inches shorter than an Al 80 so you're not as prone to whack the back of your head on your reg, and the bouyancy characteristics IMHO are much superior to Al 80's. Except for an occasional tumble at VIP time, I've never had an issue with rusting. You do have to be careful to avoid getting water in the valve, but you should be careful with any composition tank in this regard.

 

[TimAZ]

I've always been taught as most have to always keep 500 psi in reserve; if diving w/steel 80s, can you lower this in proportion, say keep a reserve of 350 psi?

I wouldn't cut my reserve regardless of volume at pressure. I like to leave a margin not only for a reseve air supply, but also for my SPG (or computer) not being particularly well calibrated.

BTW: I dive a Faber 3180 psi steel 100 and am very happy. It's "+" rated, and sufficiently negative empty that I lose 11 lbs off my weight belt making my full kit about 4.5 lbs lighter than when diving an aluminum 80. It also has the same diameter as and is about 2" shorter than an aluminum 80. Finally, with a 3180 service pressure, you can get a good fill even on boats without a particularly strong compressor.

Check out www.techdivinglimited.com for a good deal

 

[Matteo]

The only hose that will show a difference in rigidity will be your hose to the pressure guage. All of your other hoses will be low pressure and that will not be any different regarless of the pressure in your cylinder since they are only given low pressure air and that is from your first stage and does not change between a high or low pressure supply.

Mark Vlahos

OK, that is strange because I had no hose going to an SPG as I was diving w/ an air integrated computer, but there was definitely a noticeable difference in the rigidity of my low pressure inflator/Air2 hose and my second stage hose???

 

[Mark Vlahos]

OK, that is strange because I had no hose going to an SPG as I was diving w/ an air integrated computer, but there was definitely a noticeable difference in the rigidity of my low pressure inflator/Air2 hose and my second stage hose???

If there was a difference in the low pressure hoses it was probably caused by tank placement. If the tank was higher, lower, or spun around a bit the hoses might pull differently and you could easily think this was due to pressure inside the hose, but rest assured the pressure coming out of your first stage does not change enough from one cylinder to the next for you to notice, if it changes at all under otherwise similar conditions.

Mark Vlahos

 

[Mark Vlahos]

There is one thing that has been alluded to in this thread that you might consider when looking at cylinders for purchase.

A low pressure cylinder can be filled by almost any compressor out there, no matter how old or weak it might be. A high pressure cylinder when filled to its capacity of 3442 PSI can provide you with either more gas in the same external size or the same amount of gas in a smaller package. I would suggest that you consider the minimum gas requirement and maximum size of a low pressure cylinder, but actually buy or rent a high pressure cylinder that is its equivalent.

What I mean is the low pressure 95 for example is the same external size as a high pressure 119. If you have the 119 but can only get a low pressure fill you will still have 95 cubic feet of gas. If you purchased a high pressure 80 but could only get a low pressure fill you would only have 61 cubic feet of gas at 2640 PSI.

I know your original post was about a low pressure 80 but I have usen the high pressure to illustrate my point. Since you did mention the low pressure 80 the approximate equivalent cylinder is the high pressure 100. This cylinder is almost the same external size but when filled to 3442 PSI will hold about 20 more cubic feet of gas giving you a nice reserve if you should ever need it.

I know this is more information than you were asking for, but it is somthing to think about. It is also a reason to consider paying the higher price for a hig pressure cylinder, remember you can always underfill a high pressure cylinder, but it might not be the best choice to overfill a low pressure.

Mark Vlahos

 

[Stu S.]

I was a skeptic about steel. I had one in the 1970's and was glad to get rid of it. We all were. I rented a steel LP 85 late last year, and like the way it felt. In the water, it was like not having a tank at all. I purchased both the LP 95 (8 inch diameter) and the 85. The 95 is great, but the 85 is really easy diving. You can get overfills in Florida if you ask, at many places. This is a different thread. Florida Technical Scuba sells the 95 for $195 and the 85 for $175. Both are nitrox ready. Faber is a local favorite, and I like mine.

 

[Matteo]

There is one thing that has been alluded to in this thread that you might consider when looking at cylinders for purchase.

A low pressure cylinder can be filled by almost any compressor out there, no matter how old or weak it might be. A high pressure cylinder when filled to its capacity of 3442 PSI can provide you with either more gas in the same external size or the same amount of gas in a smaller package. I would suggest that you consider the minimum gas requirement and maximum size of a low pressure cylinder, but actually buy or rent a high pressure cylinder that is its equivalent.

What I mean is the low pressure 95 for example is the same external size as a high pressure 119. If you have the 119 but can only get a low pressure fill you will still have 95 cubic feet of gas. If you purchased a high pressure 80 but could only get a low pressure fill you would only have 61 cubic feet of gas at 2640 PSI.

I know your original post was about a low pressure 80 but I have usen the high pressure to illustrate my point. Since you did mention the low pressure 80 the approximate equivalent cylinder is the high pressure 100. This cylinder is almost the same external size but when filled to 3442 PSI will hold about 20 more cubic feet of gas giving you a nice reserve if you should ever need it.

I know this is more information than you were asking for, but it is somthing to think about. It is also a reason to consider paying the higher price for a hig pressure cylinder, remember you can always underfill a high pressure cylinder, but it might not be the best choice to overfill a low pressure.

Mark Vlahos

allright, that's what I'm talkin' 'bout....laymen's terms! That's an easy enough to understand way of putting it. Thanks to all who responded for the insight. A real wealth of good info on this board.