PST, Worthington or Asahi... What am I getting?

[TheTechChik]

I ordered a pair of 100 HP's for a doubles setup a couple of weeks ago. I assumed I was getting PST since that's what I had usually seen around the shop. I asked a few days later and was told that I was getting Worthington's because PST was in bankruptcy.

I just got off the phone with the shop and the tanks are in but they are Asahi. I don't know anything about Asahi but other people are telling me that Asahi's are "much" heavier, like almost 10 lbs on a doubles setup. I've also heard that the manufacturing process leaves them more succeptable to rusting. I plan on using these with Nitrox and the potential for rust doesn't sound "oxygen clean" to me.

Is any of this true? Should I insist on Worthington's or PSTs? I'm not concerned with the cost, I just want to make sure that I get the best tanks!

 

[under3483]

Hi TechChik, the simple answer is YES and YES.

Put your money back in your wallet (or purse). You do not want Asahi steel cylinders. Asahi manufactures "old fashion" HP steel cylinders. These are the same design as the old Sherwood Genesis / US Divers HP tanks (manufactured by Pressed Steel under Exemption 9791) introduced more then 15 years ago. These tanks fill at 3500 psi, not 3442 psi. This requires them to be manufactured with 7/8 x 14 UNF inlet threads, not the standard 3/4 x 14 NPSM. Only one other scuba cylinder manufactured today still uses 7/8 x 14 UNF threads (Luxfer Limited - 4350 psi fill pressure). This thread requires the use of dedicated 300 bar DIN outlet manifold / valves. You will not have the option of using International valves with a combo 230 bar DIN / yoke outlet.

Steel cylinders that are manufactured from plate have the most favored buoyancy characteristics by most divers. These cylinders will be just a couple of pounds negative when empty in salt water (with valve). Faber, Worthington and PST are manufactured by this method (deep drawn). Asahi cylinders are not. Asahi are manufactured from seamless tube, the end are heated and spun closed. An Asahi HP100 is more then 5 pounds negative when empty verses a Worthington HP100 is about 2 negative.

The exterior finish from Asahi is just a spray on zinc paint (power paint). Without question, the best and longest lasting finish for steel cylinders is a Hot Dip Galvanization process. All Worthington cylinders are Hot Dip Galvanized. Pressed Steel has used Hot Dip Galvanizing on most scuba cylinders for decades. Faber cylinders are not Hot Dip Galvanized.

The old Pressed Steel company is gone (use the search to find more then you will want to read). The new PST company is at least in part owned by an Asian cylinder manufacturer. PST has not manufactured a scuba cylinder for more then a year. Time will tell if the new PST company ever makes another scuba cylinder. If they do, then the question will be how does this Korean manuactured PST cylinder compares to the cylinders that were manufactured in the US by the old Pressed Steel company.

If you want steel cylinders now, your best choice is to go with Worthington.

Is any of this true? Should I insist on Worthington's or PSTs?

 

[Packhorse]

These tanks fill at 3500 psi, not 3442 psi. This requires them to be manufactured with 7/8 x 14 UNF inlet threads, not the standard 3/4 x 14 NPSM. Only one other scuba cylinder manufactured today still uses 7/8 x 14 UNF threads (Luxfer Limited - 4350 psi fill pressure). This thread requires the use of dedicated 300 bar DIN outlet manifold / valves. You will not have the option of using International valves with a combo 230 bar DIN / yoke outlet.

Im not to sure how true this is.
I have 4 Asahi tanks. 2x 13.6 litre (115cf) and 2x 11.6 litre (100cf) doubled up. They all have standard 3/4 thread and I have just changed the yoke valves to DIN/Yoke 200bar (232 bar).
They are heavy but it just means I need less lead. The 13.6L weigh 16.6 kgs and the 11.6L weigh 15.6 Kgs. I dont need any weight when I dive doubles.

 

[PerroneFord]

I believe DOT specifications are different. Which is why you cannot fill your cylinders in the US.

 

[Rainer]

I have Asahi HP 100s. If you're already using DIN connection, the 300 vs. 200 bar DIN connection is meaningless. They are heavier as noted above. That said, I use mine as single tanks, and for me it just means less weight on my belt, so I actually prefer them being heavy. As for the rust factor, just make sure to wash the tanks after your day of diving. Would I want to double them up? Not sure, they are heavy, but I'd consider it.

 

[PerroneFord]

These tanks require a 300bar DIN connection. Many regulators are not 300bar DIN. If they are not, they will not fit on that tank valve. Or more correctly, they will not seal. New regulators must be purchased in that case. A 300bar DIN regulator, WILL fin on both 200bar DIN tank valves, and 300bar DIN tank valves.

 

[Rainer]

Then assuming you have a 300 bar DIN reg (as I do), then this isn't an issue. If not, then definitely think about passing on these tanks!

 

[under3483]

Packhorse:
All of it is true for the Asahi cylinders imported into the US. Asahi cylinders are imported in to the US by Catalina Cylinders (aluminum cylinder manufacture in California). They are distributed by Sherwood Scuba (CDI and PSI). They are not distributed in Canada by Sherwood (Diversco) because they do not have approval/permit by TC (Transport Canada).

Below is a copy of a post on the scubaboard from a Sherwood Rep confirming the specifications.
Material: Chromium Molybdenum Steel
Construction: Spun
Inlet thread : 7/8 -14 UNF-2B
Finish: Interior Shot Blast
Exterior: Shot blast- Zinc Spray Coating- Powder Paint
Working Pressure 3500 psi
Buoyancy at Full -11.5 at 500 psi -5.2
Sherwood Scuba Rep

Im not to sure how true this is.

 

[under3483]

Rainer: Let's Compare:

Worthington X7-100
Inlet Threads
+ 3/4" x 14 NPSM
+ Industry Standard - same as all modern cylinders except Ashai and Lufer Limited
+ Larger hole - easier to VIP & tumble
Choices of Valve Outlets
+ Standard Yoke - CGA 850 connection
+ International Valve - 230 bar DIN / Yoke outlet
+ 300 bar DIN
Buoyancy
+ Negative 2# empty in salt water
Weight - Cylinder Only
+ 33.0 pounds (no valve or gas)
Exterior Finish
+ Hot Dip Galvanized
Use in Canada
+ Yes - Current TC permit

Ashai HP100
Inlet Threads
+ 7/8" x 14 UNF
+ Not Standard - only shared with Luxfer Limited
+ Smaller hole - more difficult to VIP & tumble
Choices of Valve Outlets
+ 300 bar DIN only
Buoyancy
+ Negative 5# empty in salt water
Weight - Cylinder Only
+ 36.4 pounds (no valve or gas)
Exterior Finish
+ Spray on Zinc Paint (power paint)
Use in Canada
+ No - No TC Permit

Then assuming you have a 300 bard DIN reg (as I do), then this isn't an issue. If not, then definitely think about passing on these tanks!

 

[hunter991]

I have some personal asahi tanks and I sell worthington and faber. The asahi tanks are ok but you are limited in valve choices and they are hard to find. I would try and get the worthingtons if I were you. I think you will be happier over all. Worthingtons are now my favorite brand of tank.

Brent