AL80: 3000 v. 3300psi?

[Gombessa]

I've searched a few HP v. LP threads, but had a more specific (and newb) question:

Just browsing Scubatoys and I noticed a "neutrally buoyant" 3300psi AL tank that's the same size/diameter as a regular AL80 3000, presumably 3-4lb heavier, and only ~$25 more. Any major downsides to going with a slightly higher pressure tank (are the yokes ok w/ 3300s, is it harder to get on-boat fills at that pressure, etc.)? It it just a waste of money for rec OW diving?

At the relatively low price differential, I figure I'd see more 3300s around...

http://www.scubatoys.com/store/detail.asp?product_id=AL80N

Thanks

 

[mike_s]

Some Yokes are rated different PSI. The yoke on my regulator is 4000psi.
Most K valves are rated for 4000-5000psi.
But yet most folks seem to say that yokes can't handle that extra few hundres psi.

So folks that go over 3000psi typically use DIN, which easily handles 3500psi. DIN is stronger also.


some places you might have a problem doing a 3300 fill but most can do it. Or you can plan ahead and check around before a trip and find out.

The price differential used to not be as small. The cost of the AL80 has recently gone up. I imagine the 3300 price will go up also as soon as he has to re-stock.

 

[rjack321]

Many places don't even check the rated pressure and fill to 3k in your 3300 psi tank

 

[Gombessa]

Many places don't even check the rated pressure and fill to 3k in your 3300 psi tank

I figure that's what would happen the majority of the time if you don't let them know beforehand (and maybe stick a big "FILL TO 3300" label on the tank). But even if you only fill to 3000, all it costs you is $20 and 3lb extra weight (that you would take off your weight belt to begin with) Sounds like a good deal to me if it gives you the option of going to 3300 when available, assuming as mike_s says the yoke don't choke.

 

[skynscuba]

I don't see a significant advantage. The tank is about 4 pounds less buoyant, but weighs about 3 pounds more. Okay, you save 1 pound of total weight walking down the beach, but I would guess that you will get less of a full fill than a 3000psi AL tank on the average. You might find the tank a more comfortable place to have the weight, than lead in your bcd. I have not dived with the C80, so I cannot tell you about how the trim feels vs. a S80.

 

[BKP]

I have a Catalina C80 Aluminum, and if I had it to do over, I'd go with a standard for three reasons:

1- I *often* get 3000psi fills, even when after I've reminded the fill station that it's a 3300psi tank. That means a normally 77 cu ft. tank is now 70 cu ft.

2- The tank is bottom heavy, which can mess with your trim.

3- True, you carry less weight, because it's neutral, however, once you travel to another dive location (and don't bring your own tank(s)), you need to re-adjust your buoyancy/weighting for the standard 80's they're bound to have.

I'm moving to an HP 100 3442 steel. True, I'll probably get underfilled often, however, I'm still getting 89 cu ft. at 3000psi. It's not bottom-heavy. I'll still have to deal with weighting changes (but it'll be worth it).

 

[Doc Intrepid]

It it just a waste of money for rec OW diving?

I have a Luxfer 3300 neutral tank. The tank holds essentially the same amount of gas at 3300 as the more bouyant version holds at 3000. While the external specifications are the same, the walls are thicker in places on the 'neutral' tank (to add the weight) so you need the higher pressure to contain the same volume of gas.

Whether its a waste or not depends on your circumstances.

There are some recreational divers who struggle with the amount of weight they must use, particularly in heavy wetsuits. They fill their weight-integrated BC pockets and must still wear a belt or weight harness. 4 lbs isn't much of a difference, but it might matter to some divers.

I bought mine to use as a sling stage tank. I didn't want it becoming overly bouyant as it emptied. Currently at worst it would be neutral, and as it's rarely anywhere near completely empty it does not impact my weight calcs.

Circumstances are going to be different for different divers, but I would assume that for most open water recreational divers trying to ensure that you consistently receive a full tank (e.g. 3300 psi fills) would be more of a PITA than using a standard 80.

YMMV...

 

[Gombessa]

Good points. I figured since it was still called an "AL80," the 3300psi tank would actually hold more air at that pressure than a regular AL80 would at 3000. If that's not the case, it's suddenly much more obvious why the 3300s are more of a "niche" product, at least for recreational OW.

 

[JahJahwarrior]

Tanks usually hold what they say they hold at whatever pressure they are designed for. Ergo, an al80 and a compact80 both hold 80 cubic feet of air (more like 77, but whatever) at their rated pressures. Where it gets sneaky is with low pressure steel tanks--they can get a "+" rating on their hydro that allows for a 10% pressure overfill. If the hydro guy doesn't do the exta test to give you the + rating, you have to fill to a slighly lower pressure. But, usually the amount of air the manufacturer says you can get in the tank is with that 10% overfill. So you LP85 is now a LP77 or so, something like that.

And then you always want to ask for a nice cold fill and be nice to the fill monkey--any tank with a hot fill to the right pressure will lose pressure (temperture drops, pressure drops, assuming moles of gas and size of container stay the same) You should always plan to have a few less cubic feet in your tank than you should have--assume the bum fill. If you assume your problems, they cease to be such a problem.

 

[spectrum]

The AL80 is bad enough.....
http://home.gwi.net/~spectrum/scuba_al80.html

The Neutral AL80 simply packs more aluminum onto the cylinder so as to integrate the weight and cancel the positive buoyancy. In order to not make the cylinder bigger the metal is added to the inside decreasing the volume. The forces the design to a higher pressure, 3300. Now you are in the realm of a high pressure fill with a cylinder with enough heat capacitance to take you through a cold new England night. As a design the Neutral AL80 is like polishing a turd.

That's my story and I'm sticking to it.

pete