Jim, I went to the source of tanks for my info. The Pressed Steel Co.

http://www.pstscuba.com/aapro.htm

I was wrong the HP100 is more negative than the LP104 when empty. -1.4
compared to -.7 pounds, the HP120 is -.4

As far as rust goes I believe that depends on who fills the tank and whether
their are pumping dry air or not. Mine hasn't had any rust in the six years
and it passed hydro.

Steve
ps: I'm not a tech diver but I'm studying tank spec's making plans.




on 8/5/01 6:54 AM, Jim Cobb at cobber@ci*.co* wrote:

> I guess it depends on whose specs you read this from. I guess the question I
> have to ask you is do you have 104's and HP120s and can you move back and
> forth between the two with no buoyancy changes? The folks I know who do say
> there is a considerable change.
> 
> You also have to ask yourself why do tanks rated at 120cuft at a high
> pressure weight less than 104cuft tanks at low pressure. Obviously the
> answer is that the HP120's have less robust structure than LPs. And for some
> reason the HP have a high propensity to rust internally, I have seen this
> myself.
> 
> So with the 104's you have a more negative tank and you can put 120cuft in
> them easily. They are shorter and the center of buoyancy is higher up your
> back which offsets the  weight of the light canister and other items you
> carry on your belt. You can purchase off the shelf manifolds for them which
> cost less and are easier to find.
> 
> The whole point is that if you need a set of doubles, go for the 104's,
> don't buy HP120's new or used. There is absolutely no advantage to them in
> any respect.
> 
> Jim
> -------------------------------------------------------------------
> Learn About Trimix at http://www.cisatlantic.com/trimix/
> 
>> From: Steve <sfkenney@ea*.ne*>
>> Date: Sat, 04 Aug 2001 20:40:57 -0700
>> To: Jim Cobb <cobber@ci*.co*>, Daniel Smith
>> <Daniel_Smith@co*.co*>,
>> <techdiver@aquanaut.com>, <dlhedrick@pb*.co*>
>> Subject: Re: tanks
>> 
>> I didn't miss that part. If you see I pointed out that the tanks have the
>> same buoyancy characteristics underwater which is neutral when empty. So
>> logically if you didn't need a weight belt for the LP you wouldn't need one
>> for the HP. Or what am I missing?
>> 
>> Steve
>> 
>> 
>> 
>> on 8/4/01 7:50 PM, Jim Cobb at cobber@ci*.co* wrote:
>> 
>>> You missed the part about "don't need a weight belt". I don't like weight
>>> belts, they are just one more thing to screw up and they mess up the air
>>> distribution in your drysuit. You either wear the weight you need on your
>>> back or you add it on with a weight belt, so there are no savings when
>>> climbing up a ladder with HP's.
>>> 
>>> Jim
>>> -------------------------------------------------------------------
>>> Learn About Trimix at http://www.cisatlantic.com/trimix/
>>> 
>>>> From: Steve <sfkenney@ea*.ne*>
>>>> Date: Sat, 04 Aug 2001 11:04:39 -0700
>>>> To: Jim Cobb <cobber@ci*.co*>, Daniel Smith
>>>> <Daniel_Smith@co*.co*>,
>>>> <techdiver@aquanaut.com>, <dlhedrick@pb*.co*>
>>>> Subject: Re: tanks
>>>> 
>>>> on 8/3/01 11:12 AM, Jim Cobb at cobber@ci*.co* wrote:
>>>> 
>>>>> There are some who swear by HP120's but once they try a set of LP104's
>>>>> they
>>>>> don't go back. Why are the 104's so perfect? Buoyancy characteristics. You
>>>>> can remain neutral throughout your dive and avoid a weightbelt.
>>>> 
>>>> 
>>>> Buoyancy characteristics of tanks is definitely something to study before
>>>> buying. My research reveals that the Pressed Steel tank whether low or high
>>>> pressure all have near neutral buoyancy when empty. I thought there were
>>>> other reasons why you would choose the low pressure over the high. Like
>>>> getting full or overfilled tanks, many can't pump to 3500 psi. Also a low
>>>> pressure does exert less stress on o-rings. One drawback is the overall
>>>> weight of the low pressure tank. Empty weight is 46 lbs for LB 104 compared
>>>> to 31 lbs for a HP 100. An extra 30 pounds may not mean much once your in
>>>> the water but climbing some boat ladders is where you'll feel the
>>>> difference. It's tough hoisting a set of small twin HP's over your head to
>>>> donn let along adding another 30 pounds. <g>
>>>> 
>>>> Steve
>>>> 
>>>> 
>>> 
>>> 
>> 
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> 
> 

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