USD 1800psi Steel 72's

[redrover]

Hi

I recently got a set of US Divers steel tanks. Original Hydro date was 1969. They are rated at 1800 psi. no idication of a + fill

Are these still ~72 cuft tanks, or could anyone direct me to the spec or comment on the volume of these tanks at 1800.

I realize the 72 cuft volume is based on a "+" fill and most I've seen are base rated at 2250, so I'm guessing these would be mid 60's cuft?

Any info is appreciated.

Thanks
Neil

[mistral]

If memory serves me??.. I believe those are 52.8's

[redrover]

Thanks...I should also mention they are the same size as a "normal" 2250 steel 72.

I also noted that they were + rated originally.

They look at bit to big for a 52, but I'm not sure. They are not short like the 50's.

[Seahuntjerry]

Hi Neil,
I owned a set of those Usdivers 50's and currently have another.
Look carefully they are smaller than 72 stell.
stop by and Sea Alex and Dianna (Scuba 2000)say hi from me.
Jerry

[redrover]

Hi Jerry

Thanks, these tanks are definitely not the same size as 50's. They look just like a 2250 steel 72, same size and dia, just that they are rated 1800 psi.

[duckbill]

redrover said:

Hi

I recently got a set of US Divers steel tanks. Original Hydro date was 1969. They are rated at 1800 psi. no idication of a + fill

redrover said:

I also noted that they were + rated originally.

I'm confused.
Does the original hydro stamp have the "+", or not?

[redrover]

The original hydro date is 1969 and it is + stamped.

The tanks are 3AA 1800 psi, so with the plus I imagine 1980psi.

The are stamped US Divers Corp, and have a red coating on the inside. 3/4" neck and the same physical size as a "regular" 2250 steel 72.

[duckbill]

O.K.
Here's the math:
Known: A steel 72 is about 71.2 cf at 2475 psi.
Assumed true: Your cylinder has the same external dimensions as a steel 72.

(71.2/2475)x1800= 51.8 cf at 1800 psi + 10%= 57 cf at 1980psi

Now, since your cylinders have a lower working pressure than a steel 72, it might be safe to asume that the walls may be thinner, allowing a little more volume/capacity. Notice that my "51.8 cf at 1800psi" is very close to the "I believe those are 52.8's" posted by Mistral. I would bet that his memory serves him well.
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An alternate method is to use a crossover (equalizing) whip, a cylinder of known capacity, and an accurate pressure gauge to determine your cylinder's capacity.

Please note that anytime you transfer air in or out of a cylinder, you have to wait until the air within it returns to room temperature before taking the pressure readings for these calculations. Leave the equalizing whip attached and the valves on the cylinders open until all the temperatures have been allowed to stabilized back to room temperature.
Also, emptying air out of a cylinder should be done slowly, to prevent condensation from forming on the cylinder's interior walls.

Your unknown cylinder must be empty to start.

C= rated capacity of the known cylinder in cf
c= rated capacity of the unknown cylinder in cf
S= service pressure of the known cylinder (or pressure at the rated capacity)
s= service pressure of the unknown cylinder
P= air pressure in the known cylinder
p= air pressure in the unknown cylinder
A= present cf of air in the known cylinder
a= present cf of air in the unknown cylinder


Take a pressure reading of the known cylinder to find the present pressure "P", and calculate the present, starting amount of air in it "A1":

C/S x P = A1

Attach the equalizing whip and equalize the pressure SLOWLY between the two cylinders. Allow the air in the cylinders to return to room temperature with the whip still attached and the valves open. Once the temperatures have returned to room temperature, close the valves, bleed the air from the equalizing whip and remove, and read the new pressure of the known cylinder to find the amount of air left in it "A2":

C/S x P = A2

Subtract the remaining volume from the original volume to calculate how much air transfered into your unknown cylinder ("a"):

A1 - A2 = a

Now, calculate the rated capacity of your unknown cylinder ("c") by using the rated service pressure marked on the cylinder ("s"). ("p", the pressure reading of the air now in your unknown cylinder, should be the same as the last reading in your known cylinder, since the pressures were equalized):

a/p x s = c
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On your cylinder, if you used 1800 as the rated service pressure, then add 10% to find the overfill capacity at 1980 psi.

If your known cylinder is a vintage steel 72, the known values would be:
C= 71.2
S= 2475

Check the manufacturer's specifications for any other cylinder.

"s" for your cylinder would be 1800 or 1980, depending on which capacity you are trying to find. I would use the 1800, and add the 10% once that is determined.


I hope this helps.

[redrover]

Thanks very much for the detail explanation...gives me a lot to go on.

Thanks again!

[VintageBob]

Hi Neil,

Back in the late 70's and into the 80's, I had a set of U. S. Divers twin 52.8's or 53's as they were commonly referred to. I long ago sold them but I recently acquired a single 53, which I had fully refurbished with new paint over galvanizing and a new decal. They are about 1 1/2" shorter than a 72 of the same manufacturer and they are buoyant as all get out. They are rated at 52.8 cu ft. when filled with the 10 % over charge at 1980 psi.

They work great with the single stage Mistrals as the lower pressure rating is just about at the pressure where Mistrals start getting easier to breathe.

But they were fun to dive with and the single 53 makes a nice shallow fresh water tank.

Bob

[duckbill]

From the 1970 USD catalog. May be blurry, but hopefully it can be read.

[scubadiverbob]

Terry,

The tank I dive with now has a 1969 hydro date and looks like tank (b); but has a K valve with the HP port instead of the reserve (I attach my pressure gauge to it). Does the "lifetime gaurantee" work if it ever doesn't pass hydro?

[duckbill]

No. Not for yours. The 1969 guarantee was only good for the first 5-year hydro (after the factory hydro), and only for the original purchaser who had filed the serialized guarantee card with USD within 10 days from the purchase date.

The 1970 cylinders carried the original-owner lifetime guarantee. The same type of guarantee card would have needed to have been filed with USD and the LDS of the original purchase within 10 days, the cylinder would have had to have been hydro-tested every 5 years from the purchase date, and a validated annual warranty card would have needed to have been sent to USD each year within 30 days before or after the anniversary of the original purchase date, showing that a visual had been performed by an authorized USD service representative.

Also, the warantee doesn't cover any abuse or misuse. I would imagine that water in the cylinder, or repeated over-filling would void the warantee.

ALSO, I don't believe that U.S. Divers even exists any more. I understand that the present day Aqua-Lung is not affiliated with the original U.S. Divers.

[duckbill]

I just added notes to my post to mention that air should be emptied out of a tank slowly to prevent condensation from forming inside the cylinder. The air should be transfered slowly when equalizing the pressures.
It's automatic for me when I do it, but I thought I should add that in case a reader wasn't aware of it.