Tank size question

[BigMike]

I have a steel tank that is 23" tall and has a 6.5" diameter that I need help figuring it's cubic feet size. It's an 1800psi tank that doesn't list a size or brand on it. It's from the early 70's based on it's first hydro stamp. I just had it hydro-d and it passed without any issues. It must be some size in the 60's and I want to find another of the same size so I can make a set of doubles for my Aquamaster. Any help from the vast knowledge of this forum group would be appreciated. Thanks

[21]

BIG Mike,
I am positive you tank can be Ided bur more information is needed.

To correctly ID the tank it will be necessary for you to supply all the numbers, letters and symbols around the NECK of the tank.

The size of the valve opening? -1/2 or larger?

Also does it has a reducer on top of the tank?

Where do you live in So Ill? There is a quarry down there above Cario I have read about who could possibly be of assistance

Welcome aboard,

SDM

[BigMike]

It had a 3/4" J-valve in it that was removed after the hydro. The numbers on the neck are DOT-3AA1800 1826 6()74. The () represent a diamond shape that I couldn't figure out how to type. The only other marks are from the hydro stamps. Thanks for the help.

I'm closer to St. Louis and Mermet Springs may be the quarry that you are thinking of. I haven't been there but it's a popular dive spot in this area.

[Drado]

Though I'm sure there's a way to do it for imperial units, I'm more familiar with the metric method. You can get the internal volume by filling it with water then measuring how much water you put in L. Multiply this value by the tank WP in BAR (1800 psi =~122 BAR)

Then to get your cu. ft. capacity you convert the L to cu ft.

For example: the theoretical volume of your cylinder would be 763 cu inches, or 12.5 liters.

12.5L x 122 BAR = 1,525 liters of air x 0.035 (conversion factor) = 53 cubic feet.

So, your tanks theoretically hold slightly less than 53 cu ft based on the dimensions you listed. Of course, those were external dimensions, so a more precise method would be to fill it with water first.

[sitkadiver]

Nice work Drado, I was thinking pi*r^2 times height times (1800/14.7) might also get you in the ball park.

As a short cut, "Basic Scuba" has a list of popular tanks. I'm out of town and cannot access the book right now, but the list has diameter, height and pressure in a handy table format. Maybe someone could look it up and see if there is a close match for this tank.

Good Luck

[mistral]

Do you have any pics?? If memory still serves me...U.S.Divers, had steel cylinders, at 1800psi... they were 52.8 cu.ft bottles. Check to see if there is a letter at the begining of the ser#[ it may be a "K" ]

[Herman]

Just a guess here but based on the age, working pressure and the 3/4 valve, I would suspect it's not a scuba tank but rather a CO2 bottle or maybe a O2 bottle. Both of which can be used for scuba but it was not their intended purpose.

[couv]

I agree with Herman. The birth date of the bottle points to an application other than scuba. However, it doesn't mean you cannot reassign its duty....that's vintage.

To determine the volume without filling it with water, empty it and transfer a known amount of gas into it. Take that known volume and divide it by the pressure to get a constant. To find the volume at any given pressure just multiply it times the tank's constant.

I.g. let's say you're using an Al 80 as your supply tank. Transfer out of the 80 until it has only 1500 psi remaining. We know the 80 lost 38.5 cu ft (It really holds only 77 cubic feet at 3000 psi.) So 38.5 cu ft is in the mystery tank. Now check the pressure in the mystery tank-let’s say it has 1200 psi. 38.5 divided by 1200 = 0.032 (the constant.) The working pressure is 1800 psi therefore the tank would hold 57.6 cubic feet when full. (1800 X 0.032)

[BigMike]

It may not have started out as a scuba tank but it's been used as one because I got it with a USD J-valve and boot. It has a VIP sticker from Pacific Coast Divers in CA dated 8/92. I appreciate all of the feedback from everyone. I'm going to use a newer USD J valve on it and take it to my LDS and have it inspected. I have a friend who's family is interested in diving and it will make a perfect tank for his wife & kids for their backyard pool use (under proper supervision).

I do have another question that may have been answered in a previous forum post but figured I would put it out there. I started reading the forum posts long before I had my own DH reg and I'll bet there are others out there doing the same.

I am putting together a pair of older USD steel 72's for my first set of doubles.
I have a new (old stock) USD straight bar mainifold and a couple of options for a backpack/harness. I have the tanks (yellow 2250psi with the round Aqualung decal) and i'm thinking about having them re-painted or restored. They are in good shape but have aged appropriately and have cracks and some open areas in the plastic type coating that they have. It's a thick protective coating/skin on them that has done it's job well. Do I have the coating removed and have the tanks restored/re-painted to look new or have them sanded/smoothed and then re-painted? What kind of expense will this set me back? I'll look for your suggestions/ideas as you all help me with this "project". My wife got back into riding horses so I'm allowed to have a "project or two". Getting back into SCUBA and involved in double hose diving is a real treat for me. My "better half" of over 25 years supports my new hobby but i'll have to take it slow. Thanks again for the great advice and I pray that you all have a Merry Christmas and a happy new year (now that the world didn't end yesterday)!

[swimjim]

I had some tanks like that and spent a couple nights with a stiff putty knife that I sharpened and kept sharpened the working edge on. I was able to get the tanks almost completely clean that way. I used some MEK to finish cleaning them up. Use a respirator in a well ventilated area with that stuff. Pretty nasty. From there, I did some very minor sanding and then primed and painted the tanks. I put a junk valve in them for the painting so I wouldn't mess up a good one. I used hardware store Rustoleum primer and paint. The results were not pro level, but acceptable for me. Heck, the tanks are going to be beat around on my boat. After a season of heavy diving, they have "character", but they still look great.
By the way, Karl on this site has the repro stickers that you'll need to finish things off.

Jim

[Herman]

A couple of thoughts on the USD tanks. Don't sand them, it removes metal and they may be galvanized under the paint, you don't want to mess that up. Use a paint stripper instead. Do not have them powder coated, that requires heating the tanks and it may effect the temper of the metal. If they are not galvanized under the paint, there is a cold paint on galvanizing paint that the Captain recommends. The name escapes me but if you do a search on refinishing tanks I am sure you will come up with the name..

[Drado]

The name escapes me but if you do a search on refinishing tanks I am sure you will come up with the name..

ZRC Galvilite!

[BigMike]

Thanks for the great info (as always). I did find a similar question posted on the forum and with everyone's feedback, now have a good idea of what i'm up against. Now, with alot of manual labor, some yellow paint and the new decals, I can be ready for spring. Thanks again for everyone taking the time and effort to respond to the questions that are posted on this forum. It's greatly appreciated. Be safe, Mike

[Drado]

Be sure to take lots of photos in the process!

[BigMike]

Hey Swimjim, I will need the decals for the tanks when I finish them. The ones that are on them now are a little over 5" in diameter. Do you if this is a size that I can find? Thanks again everyone for the input and I will be sure to post pictures of my progress.