PST 104's vs Worthington 130's

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Jimmer

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Location
Brantford, Ontario
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Looking for some expert advice here. I'm signed up for Naui Tech 1 in April, and need to get some larger tanks. I did intro to tech in double 72's, and my instructor suggested due to my size (6 foot 3, 220 pounds) and the fact that virtually all of his local tech divers use either 104's or 130's that I get a set of those for easier gas matching.

Anyway I have a brand new manifold, 8" bands on the way, and was planning on buying some 130's, until I picked up a used PST 104 for $60, bead blasted it and hydro'd it, and have a usesable cylinder for about $80. So I'm thinking maybe I should try to round up another one, double them, and save the money I was going to spend on the 130's for the course and gas fills.

Is there any reason why the 130's would be a lot better than 104's for wreck diving in the Great Lakes?

Thanks,
Jim
 
Get the Worthington 130s.

But I'm biased.

On the other hand, I've done quite a bit of wreck diving in the Great Lakes, and wreck diving elsewhere as well. If you're doing conservative gas plans, at fairly significant depths, you'll appreciate the cu ft of gas when planning. (Both tanks are approximately the same dimensions and volume, its a question of the internal pressure with respect to their capacity...)

Then also, my 130s balance me out very well - and I had problems with other tanks (PST 119s and Faber 95s, not 104s).

A larger issue seems to be potential issues with hydro's on the PSTs. (And I own four PST 130s...) You may find this of interest:
http://thedecostop.com/forums/showthread.php?t=34438&highlight=PST+hydro

As far as opinions go, that's mine. ;)

Best with your decision,

Doc
 
They are almost the same 104's ran up to 3500 hold about 130cf. I have a set of both and they trim the same.
 
The LP 104's will hold 140 cu ft at 3500 psi, not 130. (106.2/2640)x3500= 140.79

They are however 3.5 lbs heavier and an inch taller than the X8-130's.

The big question is whether you can get the 104's overfilled to 3500 psi. If not you will never see the extra 10 cu ft and the 130's are the way to go.
 
Either the PST 104s or Worthington 130s with be fine. Although they are both really overkill for anything less than 200ft or so. Personally I would go with Worthington hp100s or Faber lp85s if you can get them filled appropriately (3k+).

I tech dive dissimilar tanks all the time, while I don't know what course your instructor is teaching, having to "match gas plans" sounds strange to me. Unless you are talking wreck penetrations, all that you need to know is the minimum cf to get you and a buddy up to your next breathable source. Its fine for me to have to reserve 1400psi while you reserve 1100psi or any number of varients on that.

The Worthington 108s are awful beasts so I'd avoid those along with PST 130s for the reasons Doc posted.
 
Overfilling won't be a problem. I do my own fills, and my shop owner doesn't blink an eye at filling his hp100's to 4000.

Rjack, I dont know all the details just yet, but I know he encourages his students to all be on the same size tanks, I'll have to ask him specifically why he recommends that. I know one reason he has mentioned, was being able to do 2 tech 1 dives on the same charter, without having to bring stages or another set of doubles.

Right now I'm thinking I'll try to find another 104, and save the money for the time being, as I'm pretty certain I'll be going to a rebreather before I head to tech 2, and if not I can always buy some 130's down the road, and put them in the existing manifold and bands.

Any other thoughts or suggestions?
 
PST140's are great tanks. I had the chance to dive them many times. They balance out very nice. I own a set of Worthington hp130's. I really like the tanks and they feel lighter than the 104s.
 
Double 72's are not a lot of gas, so it does make some sense to get larger tanks to ensure your buddies can actually take advantage of their larger tanks.

Still, it is worth knowing how to gas match different cylinders because you will encounter it a lot. Basically, figure everyone's turn pressure based on the cubic feet used by the smallest set of tanks. This is important as those tanks potentially have YOUR reserve gas, not the guy with the small tanks.

You can do it pretty quickly by using the tank factors for the tanks involved (rated capacity divided by fill pressure at rated capacity times 100, which will give you the number of cubic feet per 100 psi).

For example, if the plan is to turn on thirds,

1. The diver with X7-100's pumped to 3500 will round down to 3300 (the nearest pressure easily divisible by 3) then divide by three to get 1100 psi for the first third - a turn pressure of 2400 psi. (3500-1100=2400)

2. His tank factor is 5.8 (100/3442 = 2.9 but times 2 since he has doubles = 5.8). So 11 times 5.8 is 63.8 cu ft used in that third.

3. The diver with 130's pumped to 3500 would turn after using the same cu ft, not the same psi, to ensure the "thirds" are equal.

4. The tank factor for the 130's is 7.5 (130/3442*100*2 = 7.5)

5. 63.8/7.5= 8.5 or 850 psi. So the turn pressure would be 3500-850= 2650 psi

With a little practice you can do the math in your head. In this case the guys with the 130's are giving up about 250 psi in the turn pressure. That is in the end not all that horrible as they are only giving up about 18 cu ft of gas for the penetration portion of the dive.

If you figure it all with 72's (TF= 5.8 for steel 72's or 4.7 for 3000 psi Faber 72's) you end up with only 47 cu ft per third and the guys with 130's are turning after only 625 psi and are giving up giving up 475 psi (and 35 cu ft) of their potential turn pressure - twice as bad as when compared with 100's. Eventually you will run out of buddies willing to dive with you.

Now, doing it this way the guy with the highest SAC, not the smallest tanks, will still turn the dive as all the "thirds" are equal - and that ensures that anyones reserve third will be equal to what anyone used going in.

Still the thing is to be sure what fill you can get in the 104's. If all you can get is 2400 or 2640, you are hauling around a lot more weight (about 26 lbs) for no more gas than you'd have in HP 100's. In practice I get 3600 in my X7-100;s just about every where and that is 104 cu ft. I often have problems getting more than 2400 psi in LP tanks (outside of N FL) and 2400 psi in an LP 104 is only 96.5 cu ft. Not a great deal when you consider the HP 100 weighs 33 lbs empty to the LP 104's 46 lbs empty.

Plus, looking at the math above, assuming you can get 3500 psi fills, if even one of the buddies "only" has 130's, you are functionally limited to 1/3 rd of 130 cu ft, not 1/3rd of the 140 cu ft you really have in LP 104's pumped to 3500 psi so there is no real upside to carrying the slightly longer and heavier LP 104 if even one of your buddies has 130's.
 
A larger issue seems to be potential issues with hydro's on the PSTs. (And I own four PST 130s...) You may find this of interest:
The Deco Stop


for whats it's worth, I just hydro'd 3 sets of PST 130's, all passed. I have 2 sets of 104's and prefer the way the 130's trim out.
 
A larger issue seems to be potential issues with hydro's on the PSTs. (And I own four PST 130s...) You may find this of interest:
The Deco Stop

Yep, your PST tanks will almost certainly fail their next hydro.
I'm a nice guy so I'll make you this offer - I'll give you $15 for yours and I'll even pick up the shipping costs :)
 

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