The Difference Between LP and HP

[Leadking]

I am late to the party but post the following comments for U.S. based cylinders:

There is only one true HP cylinder, the Luxfer hoop wrapped aluminium cylinder rated at 4350psi

Consideration of LP, <2400psi or, what we call HP >3130psi, considering that 3500psi cylinders are no longer manufactured for the U.S. market, should be based on the following:
Height of the cylinder, a tall cylinder may affect your mobility and center of gravity
Diameter of cylinder, a larger diameter will affect your center of gravity
Availability of proper fills to rated pressure
Buoyancy characteristics of the cylinder, generally HP steel are more negatively buoyant. Be careful not overweight yourself, and carry some lead to gain positive buoyancy in an emergency.
Gas needs for your particular diving activities.
Pressure ratings of your regulators

All of these items need to be considered when making a cylinder purchase, as one size does not fill all.

Good diving,
Lee

 

[tbone1004]

why do people keep saying HP steels are more negatively buoyant? It's just not true, and completely stupid to be spreading this rumour. Certain bottles are more negative than others but it has nothing to do with working pressure
PST HP80 -3.3
PST HP100/120 -1.3

PST LP80 -1
PST LP104 -3.3
PST LP 95 -3.3
PST LP120 -1.7

That disproves that rumour with PST tanks

Worthington
HP80 -3
HP100 -2.5
HP120 -2
HP130 -2

LP85 neutral
LP95 -3
LP108-2.6
LP121 -2

Fabers are a little wonky, but that's because they are without valve whereas Worthington and PST are with valve, so add 2lbs to the numbers or so
LP85 +2.3
LP95 +1.7
LP108 +3
LP120 +4

FX100 -.6
FX117 +0.2
FX133 +1.5

so with Faber we have on average a 1.5lb difference for the HP versions since L95=FX117 and L108=FX133 which correlates to the weight differences between them. This does disprove Rob's comment in Post #38 where he said they were punched out of the same plate, so not sure how the FX series would be slightly heavier since they have same diameter, length, and water capacity, but the FX are 1.5lbs heavier, so it can't be the same disc. Not relevant to this point though.

Point still stands that there is 0 correlation between working pressure and buoyancy with PST and Faber, and the difference is only 1.5lbs for Faber which is essentially negligible since most divers will be wearing at least 2lbs of weight anyway and 2lbs isn't going to be the difference in someone being able to swim a rig to the surface or not. The MP bottles made by PST *only the MP72* and Faber, the whole 3180 series are a whole different animal since those are drastically heavier than any of the others, but I saw my first MP faber for sale on craigslist last weekend and it was the MP72 which was less negative than the 3180 series. Stop spreading this completely bullsh!t rumour about HP tanks being more negative, when with most tanks, they aren't.

 

[Leadking]

Of all the cylinders listed above, Faber is the only active manufacturer. PST stopped production almost a decade ago and Worthington in 2013. Using YOUR numbers, we get the following:

LP85 +2.3 Worthington 80 (no longer available) -1 (adj for no valve) net 3.3 heavier
LP95 +1.7 FX100 -.6 net 2.3 lbs heavier
LP108 +3 FX117 +.02 net 3 lbs heavier
LP120 +4 FX117 +.02 net 4 lbs heavier

Please explain your math as available HP cylinders are clearly more negative than available LP cylinders. By the way, take you b.s. answer and shove it!

 

[rhwestfall]

Worthington (XS Scuba) Data:

 

[Leadking]

Worthington (XS Scuba) Data:

View attachment 206065View attachment 206066

These are for Worthington cylinders, See Blue Steel Scuba - Cylinder Specs for Faber
WARNING a quick review shows the buoyancy shift in LP cylinders is grossly mis-stated.

---------- Post added April 7th, 2015 at 03:10 PM ----------

Man...it is a lot more complicated then I thought. The tank that I have been diving with is a 100 steel. I'm new to the sport and I turned it up somewhat for the past two summers. I go to the wrecks BUT DONT ENTER. The deepest I do is 110 feet.
Being I did not see my name of my tanks any where on those lists can only lead me to believe the tank I have I not very good. If its not its OK...level with me.
When I looked on the tank this is what I read.
EKHR
GENESIS ST 100
SPUN JAPAN
DOT SP 12079
3442
TP 5250
Plus obvious hydro stamp

Imported from Japan by Catalina Cylinders and sold by Sherwood Scuba. Spun tanks are bricks due to construction method. The start out as pipe and the top and bottom are heated and spun shut. See http://www.scubaboard.com/forums/ta...ew-asahi-3442-100-c-f-tank-spec-question.html

 

[tbone1004]

Of all the cylinders listed above, Faber is the only active manufacturer. PST stopped production almost a decade ago and Worthington in 2013. Using YOUR numbers, we get the following:

LP85 +2.3 Worthington 80 (no longer available) -1 (adj for no valve) net 3.3 heavier
LP95 +1.7 FX100 -.6 net 2.3 lbs heavier
LP108 +3 FX117 +.02 net 3 lbs heavier
LP120 +4 FX117 +.02 net 4 lbs heavier

Please explain your math as available HP cylinders are clearly more negative than available LP cylinders. By the way, take you b.s. answer and shove it!

You're not comparing the right tanks. An LP95 should not be compared to a FX100 because it is a radically different tank, similar only in nominal capacity at working pressure. You also can only compare tanks within the same brand or at least the same process. Faber 95 about neutral rated at +1.2 without a valve
PST 95 -3.3 with a valve
Worthington 95 -3 with a valve
That would lead to hot dip galvanizing is heavier than painted, well that makes sense, there's more zinc put on it.

I made the comparisons I did because the way you made your statement, which is completely false, is that HP tanks are heavier than their comparable LP tanks, so I compared HP to LP, same tanks. FX117=L95, FX133=L108, same diameter, same height, same internal volume. They are 1.5lbs heavier when empty. You then tell me to shove it by comparing two different tanks, sure I can play that game, but that isn't valuable information unless you clarify by saying "if you want a nominal 100cf tank at working pressure, than the equivalent HP tank will tend to be more negative than the LP tank because the LP tank is physically larger and therefore has less material per liter of volume".

Well yeah, that's painfully obvious, but your completely wrong statement that has 0 validity is, and I quote "generally HP steel are more negatively buoyant". This couldn't be more wrong, because that statement generalizes all scuba tanks and it only applies to Faber where the difference is that the HP tanks are generally 1.5lbs more negative than their equivalent LP tanks. This statement does not apply to PST or Worthington, and while PST has been out of the game for a decade, they still have plenty of tanks on the market, and Worthington has only been out for a very short while, and there are still a boat load of them around. If you're going to make that statement, which I'm ok with, please say "Faber FX series tanks are more negative than their LP tanks", or "If you are comparing tanks with equivalent capacity at working pressure, the higher pressure tanks will generally be more negative". Those are correct statements.

 

[Leadking]

You're not comparing the right tanks. An LP95 should not be compared to a FX100 because it is a radically different tank, similar only in nominal capacity at working pressure. You also can only compare tanks within the same brand or at least the same process. Faber 95 about neutral rated at +1.2 without a valve
PST 95 -3.3 with a valve
Worthington 95 -3 with a valve
That would lead to hot dip galvanizing is heavier than painted, well that makes sense, there's more zinc put on it.

I made the comparisons I did because the way you made your statement, which is completely false, is that HP tanks are heavier than their comparable LP tanks, so I compared HP to LP, same tanks. FX117=L95, FX133=L108, same diameter, same height, same internal volume. They are 1.5lbs heavier when empty. You then tell me to shove it by comparing two different tanks, sure I can play that game, but that isn't valuable information unless you clarify by saying "if you want a nominal 100cf tank at working pressure, than the equivalent HP tank will tend to be more negative than the LP tank because the LP tank is physically larger and therefore has less material per liter of volume".

Well yeah, that's painfully obvious, but your completely wrong statement that has 0 validity is, and I quote "generally HP steel are more negatively buoyant". This couldn't be more wrong, because that statement generalizes all scuba tanks and it only applies to Faber where the difference is that the HP tanks are generally 1.5lbs more negative than their equivalent LP tanks. This statement does not apply to PST or Worthington, and while PST has been out of the game for a decade, they still have plenty of tanks on the market, and Worthington has only been out for a very short while, and there are still a boat load of them around. If you're going to make that statement, which I'm ok with, please say "Faber FX series tanks are more negative than their LP tanks", or "If you are comparing tanks with equivalent capacity at working pressure, the higher pressure tanks will generally be more negative". Those are correct statements.

I used the closest comparable CF cylinder. Divers, as a rule look to net breathable gas. Using tanks in water is what matters. Hauling them around in the back of your truck doesn't count.

 

[tbone1004]

Again, then use the last statement, comparing Faber tanks with equivalent nominal capacity at working pressure, don't make a blanket statement, because your blanket statement implies that a tank, which is measured in volume at sea level, i.e. liters, at 2400psi working pressure, is less negative than the same tank designed to be used at a working pressure of 3442/3500. A 95 and a 100 literally only share similar nominal capacities, they are different heights, and different diameters, they are different tanks. The same tank is a L95 and a FX117 which are identical in height, diameter, and water capacity. It is splitting hairs, but the clarification has to be there when you are making blanket statements because while you are interpreting it as nominal capacity at working pressure, that is not how tanks are supposed to be compared and especially not how they are compared when you are engineering them.

Case and point, you referenced a L95 vs. FX100, what if I used a PST LP95 or LP104 vs a E7-100, or a Worthington LP95/108 vs their E7-100? We can all agree the most common tank sizes are listed in that previous sentence, with sidemount the LP85's have become the driving force, and the HP130's had their run, but comparing tanks in the nominal 100cf range is by far and large the most common tank size. In the case above, your statement again only applies to Faber, and you could stretch it for Worthington LP120 vs X-119/120 which are all -2.

 

[Leadking]

And PST and Worthington's are no longer manufactured and only available on the used market. So if the original poster walks into a dive store, what are his buying choices?

 

[rhwestfall]

And PST and Worthington's are no longer manufactured and only available on the used market. So if the original poster walks into a dive store, what are his buying choices?

I just (December) bought 4 new Worthington LP85s.... Know where I can probably get more, as well as other sizes.... yes, supply is diminishing...