LP vs HP?

[limeyx]

Thanks in_cavediver, that is the point I was trying to make. If I can only get a 2450-2600psi fill, then an LP makes more sense, as it would have more c.f at that PSI. Now I have to do the math for larger capacity HP tanks, in the event I get off this boat and can get a higher PSI fill. Then they will make sense (if the numbers work out).

Yes, if you can only get fills of a given psi (1450) in your case, then an LP tank will give you more gas than an HP for the same rating (LP100 compared to HP100) BUT the LP tank will be physically larger and have different trim/buoyancy properties, so you aren't really comparing the same things.

 

[Leadking]

[QUOTE/Correct me if I am wrong, but don't HP tanks have thicker walls (and thus smaller actual volume) than the LP tanks. Isn't that why they can handle the higher pressure?.[/QUOTE]

Actually the wall thickness is almost the same. HP cylinders are made from a different steel and heat treated to create a higher yield. A low pressure tank has a yield of about 120,000psi while high pressure cylinders have a yield closer to 160,000 psi.

 

[limeyx]

Here is what I found:

LP 108 - 8" diam x 26" hgt, 41 lbs, -1lb (empty) - 8lbs (full) , 100 c.f. @ 2450 PSI
HP 120- 7.25" diam x 29" hgt, 48 lbs, -7 lbs (empty) - 16lbs (full), 84 c.f @ 2450 PSI
HP 100- 7.25" diam x 24", 38.7 lbs, - -7 lbs (empty) - 15 lbs (full), 72 c.f. @ 2450 psi

Again, I am using 2450 because that is the typical fill on the dive boat I use very frequently.

That HP-100 is maybe an old worthington one (and is really negative)
You might want to look at the X7 and X8 line of worthington tanks for ones that are less crazy negative too.

 

[robzr]

The newer DOT excemption tanks are making this argument moot... as per Dive Rite Express:

What Happened to Low-Pressure Cylinders?
Many experienced divers have preferred low-pressure cylinders because they are easier on regulators, have no short-fill concerns, and are more suitable for partial-pressure blending. More recently, the low-pressure 3AA cylinders (2640 psi, i.e., 2400 with a +) are being replaced by the new DOT exemption cylinders (3442 psi, no plus needed). That's because you can use the high-pressure 3442 psi cylinders as low-pressure 2650 psi cylinders if you prefer, simply by under filling. The 3442 psi DOT Exemption cylinders have the same length, diameter, and capacity at lower 2640 psi pressure as the 3AA cylinders. Even better, the empty weight of the new cylinder design has been reduced slightly, yet the buoyancy remains slightly negative when empty.

Basically if you buy a newer 3442 psi DOT exemption cylinder (XS Scuba/Worthington, PST) you get the best of all worlds.
- no +/10% overfill issues - some hydrostatic testing facilities won't recertify the +
- lighter weight than a LP of the same dimensions
- if you underfill you can match the capacity of an LP of the same dimensions
- you can fill it up to max capacity without worrying about overfilling, if that bothers you

It's like having a LP and an HP in the same tank! really....

Rob

 

[merxlin]

OK, Its been a while but I bought an LP 108. Its an XS Scuba (Worthington). I was able to drop 2 pounds (from using an LP85) after adding a 5/3 hooded vest to my 7 mil suit. My initial impression is that I like the tank. I was surprised how big it looks because of the added circumference (8" vs 7.25") vs an AL 80, and wasn't thrilled hauling a 43lb tank from the car & back. But once underwater it behaved itself very well. And I enjoyed the added capacity. No problem getting full fills on the boat, including one overfill before they realized it wasn't a HP tank).

 

[jdelprete]

I live in a mixed marriage: my wife LOVES her HP100's and I just got two LP108's to replace my LP125's today.
Still, we manage to stick together despite this almost insurmountable obstacle.

Tom, just curious but what made you drop from LP125's to LP108's?

Jim

 

[jdelprete]

Well I have read through all of this and I can see there is certainly lovers of both HP and LP tanks. Myself, I am just now looking to move form my AL80 to doubles and have been toiling over HP versus LP and the size. I know of a fella using twin LP120's and he likes them but are heavy as a mother. As to filling with both dive stores I use now I don't see any issues filling to 3000 at least and need to check with a few of them to see what their real capacities are.

Anyway, I'm thinkin that twin LP/HP 100's (give or take) may be a good place to start. As to my intentions I will be looking to start tech diving in the next 6 months or so and expect anything less than 100's for my size may be too little.

I'm all ears to anyone offering more insight to HP/LP, size, or even where to get them.

Last is anyone out there using a Zeagle Ranger BC? My BC will handle doubles without a backplate but I have some concerns still on the weight if it would be smarter to just opt for a harness setup form my double or am I just thowing money out the window.

Jim

 

[Tom Winters]

Tom, just curious but what made you drop from LP125's to LP108's?

Jim

I had to bend my arms to carry the 125's which got heavy fast 20 feet or so. The 108's I can carry with my arms hanging straight down. They are about as heavy as the bigger tanks, but easy to hump.
The 125's are easier to take off on the boat - - I'm 6'2" and the tanks rest nicely on the seat on my boat when I gear up or down. The 108's I have to slouch down a little to rest them flat.
No matter what, there's always some compromise, right?
This all said, I sold the tanks to a guy I dive with all the time, so now I get to deal with 125's and 108's.

 

[ageddiver]

Anyway, I'm thinkin that twin LP/HP 100's (give or take) may be a good place to start. As to my intentions I will be looking to start tech diving in the next 6 months or so and expect anything less than 100's for my size may be too little.

I'm all ears to anyone offering more insight to HP/LP, size, or even where to get them.

Last is anyone out there using a Zeagle Ranger BC? My BC will handle doubles without a backplate but I have some concerns still on the weight if it would be smarter to just opt for a harness setup form my double or am I just thowing money out the window.

Jim

Unless you're pressure limited as in boat fills, the decision over LP or HP usually comes down to whether you're diving mix. If you're getting into tech diving, then at some point you will. If you don't have access to boosting equipment, then LP will make more $$ sense. In terms of size, 95-100CF is likely all you'll need for a while - for most, more than 100 is not worth the added weight and size. LP 120's are truly huge and unless you are too I'd stay away. A pair with stage bottles and they'll have to winch you around the boat.

If you're serious about tech diving, then lose the BC and get a backplate and wings. Your BC will never trim properly, you won't be able to attach gear properly, and with steel tanks it'll likely tear itself apart anyway. Based on your location, you'll be diving dry and the added weight of the backplate will be welcome as you won't have to put much or any on a belt.

Bob

 

[jdelprete]

Thanks for the info Tom and ageddiver. I am looking to move from my Zeagle BC to a harness system as you said and agree that while I'm 6'1" 100's are a good start. Thanks for your time guys.

Jim