How to know if tank is LP or HP and how big

[SuperMiguel]

Does any of the numbering on a tank specify if they are LP/HP and what size? ie steel LP 108

 

[TSandM]

Working pressure is stamped on the tank. There are also markings on the tank to tell you of what metal the tank is made. The total volume of the tank is NOT marked on the tank, but can often be inferred from the outside dimensions. To be SURE of the volume of a tank, if the combination of working pressure, dimensions and weight are not conclusive, requires doing something like transfilling into a known volume container.

 

[Phil_C]

Metal Type: 3AA = Steel / SP6498, E6498 or 3AL = Aluminum
Working Pressure: Maximum pressure lbs / inch2 (steel = 2250, al = 3000-4000 psi)
Serial Number: 12345 = Unique to tank Manufacturer
PST = Manufacturer of the Cylinder Hydrostatic Test Date / Hydrostatic Tester’s Mark
6 1996+ = Hydrostatic Test Date (Month, initials of tester, year)

A while ago when I asked the same question about tank markings somebody sent me this - it might help - Phil

 

[SuperMiguel]

Nice thanks how about size? Like do I know if it is 100 vs 95 vs 108 etc

Sent from my Nexus 5 using Tapatalk

 

[Phil_C]

UK tanks have a number of other markings usually - one of which is empty weight of tank (minus valve), another of which is 'water capacity' in litres, neck thread size and pitch and wall thickness in mm. For tanks with these markings you can easily tell if they are 10/12 or 15 litres and so on. I am not sure about US tanks.

UK (IDEST) markings also give you working pressure, test pressure and a 'service' pressure which can develop when the tank is heated to a specified temperature at full fill.

I'm afraid I have very little experience of US tanks so don't know if they have an equivalent. - Phil

 

[Nwcid]

Sometimes you just know because of what they look like, once you learn. Some are harder and you have to go by measurements. Here is a chart that list the specs for many different tanks, Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan There are several other places that have similar charts, this was just the first one on google.

 

[TSandM]

As I said, size is not marked on the tank. You can refer to a cylinder specification chart like THIS one, and compare the dimensions and weight of your tank with what they list, but you can see that many tanks are pretty similar. The only way to be SURE of a completely unknown tank is to determine the pressure drop when removing or adding a known volume of gas to the tank. You can do this by transfilling from a tank with known volume.

 

[SuperMiguel]

ya im just buying tanks from craiglist guy says they are 108, but size wise they are very similar to 104/100

 

[tursiops]

Size IS marked on some tanks. It will appear as "S80" for example, or "S040" on most AL tanks. Some newer steels are so marked, like "E7-80". Older steels are best judged by size/weight, or best of all by the transfill to a known tank and calculate from the before and after pressures of each.....once everything has gotten to equilibrium temperature again!

---------- Post added December 9th, 2013 at 02:14 PM ----------

ya im just buying tanks from craiglist guy says they are 108, but size wise they are very similar to 104/100

Ask him to copy the tank markings for you, or better yet send you a picture or two. You can see the working pressure from that, and the age, and the manufacturer. You should be able to tell pretty quickly if they are OMS 108's or not. Also - important! - check the threads on the valve, and see if they are modern 3/4 or older 7/8 (which is NOT a diameter, it is a smaller valve diam than the 3/4). If you ever want to change the valve, you'll want 3/4 threads.

 

[SuperMiguel]

i know he said they are about 6-7 years old, hydro within 2 years, and visual july this year.. He is selling 4 for $600, he said they may be LP 100's but it allowed overfill 10% so i guess it holds the same as 110