Question about propane tank capacity

[nodine]

If the metal plate on an RV propane tanks says 12.2 gallons does that mean when the tank is at 80% volume it holds 12.2 gallons or is that the 100% volume capacity which is not achievable since 20% of the tank volume must be vapor?

Bob

[Old-Biscuit]

Data Plate is Tank Capacity----12.2 gallons
9.4 gallons usable capacity (40#)
*80% Fill Valve OPD shuts off---gauge should read FULL

[bsshog40]

Mine are suppose to be 30# tanks with each holding 7.1 gal. But at 7.1 gal, that would be 29.962 pounds. No room left for 20% vapor. I just had one tank filled this morning and it held 6.8 gal..There was a bit in it when I took it to fill. By my calculations, I should have at least 6 pounds of space in my tank to accomodate 20% of vapor/gas, which amounts to a little over a gallon of extra room. So my tanks would have to be 35#'s correct?? Or am I missing something? Lol

[KanzKran]

Originally Posted by nodine

If the metal plate on an RV propane tanks says 12.2 gallons does that mean when the tank is at 80% volume it holds 12.2 gallons or is that the 100% volume capacity which is not achievable since 20% of the tank volume must be vapor?

What Old Biscuit said - data plate shows 100% volume on ASME tanks.

Originally Posted by bsshog40

Mine are suppose to be 30# tanks with each holding 7.1 gal. But at 7.1 gal, that would be 29.962 pounds. No room left for 20% vapor. I just had one tank filled this morning and it held 6.8 gal..There was a bit in it when I took it to fill. By my calculations, I should have at least 6 pounds of space in my tank to accomodate 20% of vapor/gas, which amounts to a little over a gallon of extra room. So my tanks would have to be 35#'s correct?? Or am I missing something? Lol

DOT tanks, on the other hand, are normally identified by the volume at 80% fill (usable volume). But you can look at the data on the ring. WC is Water Capacity in pounds when filled to the very top. Propane is about 51.5% as dense at liquid propane at room temperature, so multiply the WC value on the ring by 0.515. Then multiply by 0.8 for the 80% value. That should be around 30 pounds. Again, assuming those are DOT cylinders.

My 20 lb grill tanks show 47.6 lb WC. 51.5% of that is 24.5 lb, and 80% of that is 19.6 lb, which is about what they weigh once the 19 lb Tare Weight (TW - also on the ring) is added when I check tanks after filling.

My ASME tank.

[Old-Biscuit]

30#DOT (portable) cylinders hold 30# of Liquid Propane
Propane weighs 4.2# per gallon
30/4.2=7.14 gallons

[Ray,IN]

DOT tanks, on the other hand, are normally identified by the volume at 80% fill (usable volume). But you can look at the data on the ring---.

DOT portable cylinders are what is used by the RV industry and your BBQ grill, I've never seen a small ASME cylinder used by RV'ers.

Difference between ASME and DOT cylinders:

https://www.propanetankstore.com/dot...k-differences/

https://www.propanetankstore.com/siz...-200-lb-tanks/

[Old-Biscuit]

Originally Posted by Ray,IN

DOT tanks, on the other hand, are normally identified by the volume at 80% fill (usable volume). But you can look at the data on the ring---.

DOT portable cylinders are what is used by the RV industry and your BBQ grill, I've never seen a small ASME cylinder used by RV'ers.

Difference between ASME and DOT cylinders:

https://www.propanetankstore.com/dot...k-differences/

https://www.propanetankstore.com/siz...-200-lb-tanks/

That would be because ASME are Tanks...not cylinders

Motorhomes use ASME Tanks
Trailers/Campers use DOT Cylinders

[nodine]

Originally Posted by Old-Biscuit

Data Plate is Tank Capacity----12.2 gallons
9.4 gallons usable capacity (40#)
*80% Fill Valve OPD shuts off---gauge should read FULL

Thanks Old-Biscuit, that is what I was looking for.

Bob