Why the E8-130 (LP-104)...

[MacLeod]

I have talked to and read many people's preference for the E8-130 (LP104). Most have said that this stems from its greater empty negativite buoyancy.

Question: Comparing the E7-120 and E8-130...acknowledging the 10 cuft greater gas difference in favor of the 130 and 2.46 inches shorter...

If the E8-130: Empty Buoyancy of -4.8# and Empty weight of 42.2#

and the E7-120 has a Empty Buoyancy of -1.3# and Empty weight of 36.6#...

Wouldn't a 5lb cylinder weight (V-weight) bridge the 130's advantage (again acknowledging 10cuft. less gas).

E7-120: -1.3# + -5#= -6.3# Empty Buoyancy
36.6# + 5#= 41.6# Empty weight

Both the empty buoyancy and empty weight seem preferable to those of the E8-130...ie both slightly lighter on land and more importantly -1.5# more neg. buoyant.

Now that all have same service pressure...why are the 130's dimensions preferred by so many? Is there some inherent benefit to a slightly wider and slightly shorter cylinder?

Thank you.

 

[jonnythan]

I wonder about that myself.

I keep hearing that high pressure cylinders are bad, but then a lot of people fill their low pressure cylinders to well above the rated pressure. Now that you can "legally" fill the low pressure cylinders to 3442 psi...... what do people propose you do? Only get them filled to 3000 psi? The E7-120 is so close to the E8-130... whatever they propose you do for the new E8, the same applies to the E7, so I dunno. It all seems so silly. The extra -3 pounds might be nice to take a little bit off your weight belt, but I also keep hearing that the rated tank buoyancies are total lies.

Who knows.

 

[runvus4]

I personally like the HP 120's or E7-120s. Some people like the E8-130s for a variaty of reasons, the ones I think are more relevant first...

- Length of tank/trim considerations, some people find the 120's just too long and the 130s just right, or vice versa

- Bouyency, as said it can potentially be equalized by adding weights somehow, either v-weight, trim weights, weight belt or what have you.

- 130s hold more gas at equal PSI than the 120s, in a double config, it can be 20cf at 3442psi. If the 20cf isn't enough to modify your dive plans, then it is irrelevant. If it is enough to modify your dive plans/safety factor than it is a big deal... As well, people who PP blended can drain O2 and HE storage tanks a few CF longer for the equal PSI level, and thus be more efficient without getting a Haskel.

- Psycological... people always liked the idea that they can "overfill" the 104s to get 130 and thus have more air than a 120, but often discounted that they could just "underfill" the 120 and get the same low pressure gas blending benefits, albeit with slightly less total gas.

 

[pescador775]

Runvus, you make some interesting comments. It also seems that PST is aware that some people are used to diving 8 inch dia tanks and wanted one in their new lineup. So, when a direct comparison is made with the competition, the PST tank holds more air with less dead weight. This might appeal more often to new buyers. Some experienced divers might object because of the PP mixing issue since they can't get it through their heads that a HP tank can be underfilled for this purpose while leaving a safety margin. However, some don't want a margin, they want to feel that they are getting something for nothing by overfilling a LP tank. This is a psychological issue as mentioned before. There is a real issue with some drysuit divers who want a heavy tank. For those who want this new tank but are wondering what the new tank will do to bouyancy and trim characteristics of wings and drysuits, some creative measures might be needed. Trim weights have been mentioned but I'm not sure how this would work with a single tank without a boot. Some boots will accept a trim weight. A weight can also be clamped between the tanks in a double set. A V weight might work if wings are used. This would alleviate surface buoyancy problems in some cases.

 

[Soggy]

The E8-130s are not -4.8 negative like the LP104s. The E8s have very different bouyancy characteristics than their LP counterparts....

The E8-130s are -1.8/-11.55 vs LP104s -4.8/-12.6.

PST E-series chart

 

[MudDog]

The E8-130s are not -4.8 negative like the LP104s. The E8s have very different bouyancy characteristics than their LP counterparts....The E8-130s are -1.8/-11.55 vs LP104s -4.8/-12.6.

Yeah, you know that is interesting...I too have been seeing a lot of different number on this. Soggy, I am familiar with the numbers (Lloyd Bailey fact sheet) and several others and there does seem to be a lot of discrepency...so I called PST directly.

They said, that according to the info given them by their engineering dept. dated 5/9:

E8-130: -4.8 and -14.6
E7-120: -1.3 and -10.3
(That is of course empty and full buoyancy).

I don't know which is actually right, but that is their "official" party line.

For what its worth.

MudDog

 

[Soggy]

MudDog once bubbled...

...so I called PST directly.

They said, that according to the info given them by their engineering dept. dated 5/9:

What does PST say about the LP104s as the rated bouyancy?

 

[MudDog]

What does PST say about the LP104s as the rated bouyancy?

They said they are not producing either the LP or HP line anymore(as you probably know).

I did not ask them about the old LP104's buoyancy.

They did happen to mention that the HP-120 and E7-120 have maintained the same buoyancy characteristics (-1.3 and -10.3). I would *not* imagine however, the same can be said of the new E8 line (staying the same) as they are using a different material (chromium molybdenum).

Sorry, can't really help you on that.
If you want to reach them, their number is 1-800-811-4530 and hit 1 as Tom Ivey is out on vacation.

If you call, would like to hear what you find out.

MudDog

 

[Braunbehrens]

A lot of the tank stats out there are wrong, especially the ones from PST. When you call them on it they always say " this is according to our engineers ". It's a "calculated" weight. They need to get new calculators over there, or maybe a $10 fish scale!

In my experience the pst's are less buoyant than advertised, especially the HP tanks.

 

[MacLeod]

Thanks everyone for your replies...really helpful!!

But what about diving trim characteristics? Assuming a tall diver (i.e. is tall enough to handle the 120s greater length), would one tank's dimensions (LP104 (E8-130) VS HP120(E7120)) be preferable?[120 (7.25"D 28"L) , 104 (8"D 25.56L)] Does the 104 feel like it sits high/tall on your back making you feel "back heavy"?

I guess what I am asking is, any ideas on which dimension would be more "enjoyable" to have strapped on your back as a single and or double?

Thanks again.