What is the internal volume of a OMS 112 cu ft?

[Slamfire]

I'm getting confusing information. TDL says a OMS 112 carries 108 cu ft @ 2640 psi. Huron Scuba says it carries 112 cu ft. Both tables say this cylinder weighs 41 lbs. Faber's website says their 8" diam 41 lb cylinder has 1037 cu in or .6 cu ft internal volume.

2640 psi / 14.7 psi per atm = 179.59 atm

179.59 atm x .6 cu ft internal volume of cylinder = 107.7 cu ft or 108 cu ft.

But the tank's shoulder actually says 112 cu ft, 2400 psi and the "+" which means 10% overfill to 2640 psi. Sooo, which is it, 108 or 112? And why in the world is it so confusing?

All I want is to land on a tank factor. Is it 4.24 cu ft per 100 psi or 4.09 cu ft per 100 psi? May be a should just leave it at 4 flat and chuck whatever is over 4 to conservatism.

 

[cool_hardware52]

I'm getting confusing information. TDL says a OMS 112 carries 108 cu ft @ 2640 psi. Huron Scuba says it carries 112 cu ft. Both tables say this cylinder weighs 41 lbs. Faber's website says their 8" diam 41 lb cylinder has 1037 cu in or .6 cu ft internal volume.

2640 psi / 14.7 psi per atm = 179.59 atm

179.59 atm x .6 cu ft internal volume of cylinder = 107.7 cu ft or 108 cu ft.

But the tank's shoulder actually says 112 cu ft, 2400 psi and the "+" which means 10% overfill to 2640 psi. Sooo, which is it, 108 or 112? And why in the world is it so confusing?

All I want is to land on a tank factor. Is it 4.24 cu ft per 100 psi or 4.09 cu ft per 100 psi? May be a should just leave it at 4 flat and chuck whatever is over 4 to conservatism.

If you know the empty weight, and the empty buoyancy with an fair degree of precision and you know the density of steel (495 lbs / cu ft) you can calculate the values you desire.

Tobin

 

[Rainer]

Tank factors are supposed to make your life easier. Just call it 4.

 

[Slamfire]

I just tried out some numbers. If they were using a technical atmosphere (14.2 psi) instead of a standard atmosphere (14.7 psi) then you end up with 112 cu ft instead of 108.

I guess it's technical atmospheres for technical diving . So 108 cu ft if you're doing recreational diving and 112 cu ft if you're doing technical diving.

 

[elan]

As you are in Canada all new ones (since 2002 ? not sure about the date) they are al reated in bars and all LP cylinders are 184 bars. There is no + rating here. My worthington LP108 has a tank factor of 8.2 ( doubles) if I remember correctly Fabers are the same. PST 104 which are in fact 106 has a factor of 8. It should not be a big deal though

 

[Slamfire]

These have original hydro dates of 2001 and 1997. They still do have the "+" stamp and have "112 cu ft" stamped in the shoulder. The seller was telling me they were LP 120's. He was figuring out 112 cu ft @ 2400 equals 120 cu ft @ 2640. Which is what really started me looking into this mystery.

Initially I was looking into finding out specs about weight and bouyancy to figure out how to adjust the lead I carry. But then I found conflicting information about cylinder capacity. I agree with you that it is really no big deal -- 4.08 and 4.24 are both just plain 4 in real life. It's a little bit more relevant when you do compare it to a LP 120. But I think I'm safe concluding they are not LP 120's because they have "112 cu ft 2400 psi" stamped in the shoulder.

Do you guys know if Faber coats the inside of cylinders? I'm asking because I recall my dad had an old Spanish Nemrod steel with what looked like a glassy coating inside. When I looked inside these OMS everything had a dull dark grey finish (carbon steel?). There were no shiny spots or reddish discolored areas. The cylinders were not in use and in storage for about 6 years. All that time they had 800 psi of a hypoxic mix with only 15% O2. I was thinking the low 02 may have helped avoiding rust.

 

[elan]

No they do not coat them inside AFAIK. I have lp85 s from 2002 and they have a very bit o flashrust from last hydro.

No those are not 120 s for sure. They are 108(112) at 184 bars 2640 psis not at 2400 psi like he thought

BTW mine says DOT 2400+. TC 184. Check if there is a TC stamp there it should say the pressure in bars

 

[Slamfire]

Yep TC 184 in there. Apparently faber has a "phosphatized internal treatment" that explains the non-shiny dark grey color.

Phosphatizing is another name for Parkerizing.

 

[elan]

Yep TC 184 in there. Apparently faber has a "phosphatized internal treatment" that explains the non-shiny dark grey color.

Phosphatizing is another name for Parkerizing.

View attachment 100519

Good to know. Thanks