Survivair tank?

[Ron]

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... _555wt_930

I snagged this for 20 beans. Any idea how much air it holds? I figure if it is 4 inches in diameter and roughly 14 inches long then it should be about 14 or 15 cubic feet if it were flat on both ends. I know to do proper math we need the short length and the cylinder wall thickness, but I don't have that information. Any guesses?

I am thinking of rigging a doublehose to it with some parachute cord and making a vintage style hang bottle out of it .

[antique diver]

There is your perfect little stage cylinder to strap beside you when you are diving a double hose and need an air supply for a BC, drysuit or backup single hose reg.
Also handy for filling your tires, air mattresses and blowing air on charcoal to start your grill up faster.

Looks to be about the size of the one I use for all the above. I never even took the time to try to figure out the volume, but I bet you'll love it.

[antique diver]

Here is the little fellow hanging below my right arm, being used as an air supply for my drysuit. Note the mask that I got from you also went on that dive.

[luis]

When you get it hydro just measure the water volume... either by volume or water weight.

I prefer to measure the weight of the empty tank with no valve and then the weight of the tank with water in it. I can calculate a fairly precise volume from that.

[Ron]

That's a great idea Luis, thanks!

[Creed]

I have something like 5 of the later Survivair tanks, but I think they have a different neck and thread. Survivair was the fire fighting equipment division of US Divers, and they used lightly modified SCUBA gear at the start.

[kingairpilot]

I was going to bid on that tank but forgot to watch the auction. Glad it went to someone who is going to use it.

[eodman]

I snagged this for 20 beans. Any idea how much air it holds?

Take the reg off and fill the tank to the rim with water, poor the water out into a metric measuring container (beaker or what not) use that as the floodable volume. Convert liters to SCF and use a regular avail gas formula to get the available SCF at whatever pressure you plan to jam it to...

hope that helps...

[Ron]

Once I have the true volume of the tank by measuring the volume of water that it will hold, I could then multiply that by the service pressure, and divide by atmospheric pressure (14.7 PSI). Then I should know how much air is really in there, right?

[eodman]

Once I have the true volume of the tank by measuring the volume of water that it will hold, I could then multiply that by the service pressure, and divide by atmospheric pressure (14.7 PSI). Then I should know how much air is really in there, right?

Yes, (but add the atmospheric before you divide) that will give you how much air the tank will hold...if you want to know how much is available to the diver use the following formula, since the regulator will use some amount of pressure to drive it beyond which it will fail to work.

Va = {[(Pc - Pm)+14.7] / 14.7} x FV x N

Where:
Pc = Measured cylinder pressure, psig (or service pressure)
Pm = Minimum pressure of cylinder, psig (minimum to drive reducer/regulator)
FV = Floodable Volume (scf) (have to convert from liters)
N = Number of cylinders
Va = Capacity available (scf)

You can then use air consumption formulas to figure out how long that supply will last given a certain depth, assuming you are heading for the surface at a given rate of ascent. Divers can use from 0.5 scf per minute (relaxing) to 2.5 scf per minute (freaking out cuz they just ran out of air)...

[Ron]

Wow man, thanks!

[Robohips77]

Pretty neat . It even has the stem gauge for psi in the valve. Very cool. I will have the crossover with me so we can hydro it ourselves!!!!!!!!!!

[Ron]

Holy self inflicted necro thread batman...

I ended up trashing the old survivair style tank a few years ago. It was so rusty inside that I didn't feel safe using it. I did, however, find another one for a song so I bought it. It even came with a Selpac post valve from 1961. This tank is dimensional identical to the USD survivair tank, but is stamped with Global manufacturing's insignia and dated 1961. This one was not trashed inside. I ended up filling it with water, and doing all the math. @2450 PSI, it holds an even 12 cubic feet of air. It is going to be my bailout bottle for when I don't feel like diving with a buddy

BTW, old Selpac valves, while externally almost identical to USD ones, have a different internal structure that I find interesting. Anyone have any experience with the old 60's Selpac post valves?