Tank ID Question - PST 1800 PSI

[mahjong]

Does anyone know the specs (volume, buoyancy) for a PST tank marked DOT-3AA 1800. The manufacture date appears to be 11 80. They are approximately 21" tall and 6.9" in diameter. I have a pair of them attached to a Scubapro J Valve Doubles Manifold. I wanted the manifold but had to buy the whole rig. The owner couldn't read the very faint markings. From pics and measurements I thought the tanks were MP72's, as they are almost exactly the same size. After cleaning the tanks I can (barely) make out the markings--they are definitely PST 1800 psi tanks, with a black coating that I cannot be sure is original.

 

[duckbill]

That sounds about right for 45 or 50 CF tanks.

If you don't want them and they look good inside, I may be in the bay area sometime later this month. My son is approaching diving age, and I'll be in the market for such a size cylinder or two.

 

[mahjong]

Thanks, Duckbill.

45 or 50 cf would be nice, though I was hoping they might be 60+ cf.

There is air in the tanks, so there's hope for the insides looking good, though the last hydro was 1985 (the only post-factory hydro). The rig--two tanks, manifold, bands, plastic backpack--weighs only 50 lbs (again, under 500 psi of air in the tanks). My doubled MP72's--same outer dimensions on the tanks, manifold, no backplate--weights 76+ lbs (tanks are full of air, though).

So, I'm loving the idea of doubling up these PST's--so much lighter than my 72's. Less air, yes, but I'm not a cave diver and I'm freezing in CA water before I can come close to breathing down my LP95 single tank.

But do keep in touch. I've only just received these tanks and they are most unique to me. I might have a change of mind after the thrill wears off.

I hope someone can provide more specific info on the tanks. No spec sheet I can find includes them and my google searches are coming up blank.

That sounds about right for 45 or 50 CF tanks.

If you don't want them and they look good inside, I may be in the bay area sometime later this month. My son is approaching diving age, and I'll be in the market for such a size cylinder or two.

 

[mahjong]

Hard to believe there isn't a Scubaboard seasoned veteran out there with some info to pass along on these tanks.

Does anyone know if PST is still in business? Their website seems poorly maintained and the email address they provide does not work.

Does anyone know the specs (volume, buoyancy) for a PST tank marked DOT-3AA 1800. The manufacture date appears to be 11 80. They are approximately 21" tall and 6.9" in diameter. I have a pair of them attached to a Scubapro J Valve Doubles Manifold. I wanted the manifold but had to buy the whole rig. The owner couldn't read the very faint markings. From pics and measurements I thought the tanks were MP72's, as they are almost exactly the same size. After cleaning the tanks I can (barely) make out the markings--they are definitely PST 1800 psi tanks, with a black coating that I cannot be sure is original.

 

[duckbill]

Hard to believe there isn't a Scubaboard seasoned veteran out there with some info to pass along on these tanks.

I thought I did. How much more information do you want?

O.K. See those cylinders in my avatar? Those are 1800 psi PST cylinders. They are 21 1/4" long and 6.9" in diameter (sound familiar?). The original hydros have a "+". They hold 50 cubic feet each at 1980 psi (1800 + 10%). Were they not originally "+" rated, they would hold 45 cubic feet each (1800 psi). Are the original hydros on yours "+" rated, or not?

Speaking for my particular cylinders, set up as doubles, on the original Healthways manifold and backpack, they are about five pounds more buoyant than a single steel 72 with an "standard" valve when at 13 cubic feet of reserve. Yours may be different, if for no other reason than perhaps being on a manifold of different mass.

 

[mahjong]

Thanks, Duckbill. I must have missed all this information in your first reply: "That sounds about right for 45 or 50 CF tanks."

At the risk of missing even more, can I ask which steel 72 you are referring to--the old LP72 (2250 psi) or the shorty MP72 (3000 psi). Since the MP72 has almost the exact outer dimensions as the PST 1800's, I'm guessing you might mean these? If so, without valve, the MP72's are -11.1 lbs full (+10%) and -5.7 lbs empty. Are these the correct numbers for comparison?

In any case, if you could give me direct estimates of the buoyancy of your rig--full and empty (with your manifold/bands is fine)--that would be hugely helpful. My tanks are out for hydro and, assuming they pass, in one week I will have them rigged to a modern Scubapro isolation manifold and bands and plan to take them right out for a dive, and I will be winging it with weighting. So any more buoyancy info would be appreciated, if you know. Thanks again!

I thought I did. How much more information do you want?

O.K. See those cylinders in my avatar? Those are 1800 psi PST cylinders. They are 21 1/4" long and 6.9" in diameter (sound familiar?). The original hydros have a "+". They hold 50 cubic feet each at 1980 psi (1800 + 10%). Were they not originally "+" rated, they would hold 45 cubic feet each (1800 psi). Are the original hydros on yours "+" rated, or not?

Speaking for my particular cylinders, set up as doubles, on the original Healthways manifold and backpack, they are about five pounds more buoyant than a single steel 72 with an "standard" valve when at 13 cubic feet of reserve. Yours may be different, if for no other reason than perhaps being on a manifold of different mass.

 

[duckbill]

I don't know anything about an "MP72". I'm refering to the good, old standard steel 72 which is neutral in sea water with most valves at 13 cubic feet of reserve (450 psi).

My paired 50s at 13 cubic feet of reserve (260 psi) are 5 1/2 pounds buoyant.
They are about 1/2 pound negative when "full" as 1800 psi cylinders, and about 1 1/2 pounds negative when "full" as 1980 psi cylinders (1800 + 10% if "+" rated).

Your results may vary.

 

[mahjong]

Thanks, Duckbill. That's perfect. I can work with those numbers.

The MP72's, again, are almost identical to the 1800's in outer dimensions, but when full as a pair they are more than 22 lbs negative, not including the manifold and bands.

Do you know when PST began making these 1800's? Are these the white twin steel tanks we see in Bond's Thunderball (the tanks worn by the 'good guys'), which was released in 1965? Or were these tanks not yet around then? Mine have a black vinyl coating and were born in 1980. Are these newer than your galvanized pair?

Thanks again!

I don't know anything about an "MP72". I'm refering to the good, old standard steel 72 which is neutral in sea water with most valves at 13 cubic feet of reserve (450 psi).

My paired 50s at 13 cubic feet of reserve (260 psi) are 5 1/2 pounds buoyant.
They are about 1/2 pound negative when "full" as 1800 psi cylinders, and about 1 1/2 pounds negative when "full" as 1980 psi cylinders (1800 + 10% if "+" rated).

Your results may vary.

 

[Luis H]

I have a very similar set of doubles (21” tall x 6.85” OD)

They are stamped for 1800 psi and they have a + therefore their working pressure is 1980 psi. The first hydro was plus stamped and during the last hydro on 6/11 they both received a + stamp again.

I measured the internal volume using a precise scale and measuring the weigh of the water capacity and at 1980 psi they hold 46.5 cu ft and 46 cu ft.

The average wall thickness for the two tanks is 0.147” and 0.134”, measured with ultrasonic test equipment.

The REE numbers for these two tanks are 47.1 cc and 46.3 cc.

In salt water the set is 1.6 Lb negative when full (tanks, bands, and manifold, no regulator); this makes them 5.3 Lb positive when empty.

The combined two tanks hold 92.5 cu ft of air at STP (standard temperature and pressure), since air at STP is about 0.075 Lb/ cu ft, therefore the tanks hold 6.9 Lb of air (when full).


Added:
My tanks are galvanized, but Scubapro did offer a variety of tanks with a black coating above the galvanized finish.

 

[mahjong]

Thank you, Luis, for the excellent data.

Who makes your tanks? Also PST? I'm wondering why you mentioned Scubapro? Did Scubapro distribute these tanks at one time? I am only aware of two manufacturers whose tanks were distributed by Scubapro: Norse Industries and then Faber. But there could be others that I have not heard of.

Thanks again!

I have a very similar set of doubles (21” tall x 6.85” OD)

They are stamped for 1800 psi and they have a + therefore their working pressure is 1980 psi. The first hydro was plus stamped and during the last hydro on 6/11 they both received a + stamp again.

I measured the internal volume using a precise scale and measuring the weigh of the water capacity and at 1980 psi they hold 46.5 cu ft and 46 cu ft.

The average wall thickness for the two tanks is 0.147” and 0.134”, measured with ultrasonic test equipment.

The REE numbers for these two tanks are 47.1 cc and 46.3 cc.

In salt water the set is 1.6 Lb negative when full (tanks, bands, and manifold, no regulator); this makes them 5.3 Lb positive when empty.

The combined two tanks hold 92.5 cu ft of air at STP (standard temperature and pressure), since air at STP is about 0.075 Lb/ cu ft, therefore the tanks hold 6.9 Lb of air (when full).


Added:
My tanks are galvanized, but Scubapro did offer a variety of tanks with a black coating above the galvanized finish.