Conversion of Cylinder sizes

decoweenie · 8th August 2007, 03:45

Quote: (Originally Posted by 2002scubasteve)

How can this be?

Since you divide by a higher pressure, obviously you get a lower displacement L.

As the Imperial unit gives the rated capacity (in 95 cf, for example) at certain rated pressure. They go hand-in-hand and must be used together.

The moment you raise the pressure, the rated capacity is no longer the same (at 95 cf). It should increased.

In Metric unit, the L is the equivalent water displacement of the tank. So multiplying by pressure gives you the internal gas capacity.

For example, there are 7L with 200 bar tanks, and also 7L with 223 bar tanks available. The external size of these 2 tanks are the same and should displace the same amount of water when submerged.

***jradomski*** · 8th August 2007, 04:18

Quote: (Originally Posted by decoweenie)

This is a rough calculation...

Convert cf into free liters using: cf * 28.3 = free liters
Convert rated pressure into bar using: psi / 14.5 = bar
Convert free liter at pressure into displacement: free liter / bar = L

For example, 80cf 3200psi into Metric equivalent:

80cf * 28.3 = 2,264 free liters
3200psi / 14.5 = 220 bar
2264 free liters / 220 bar = 10 L

As said, just roughly...

except most al "80s" are actually 77.4 cuft when using air..

***jradomski*** · 8th August 2007, 04:23

Quote: (Originally Posted by 2002scubasteve)

I have used the conversion formula given here cuFT/0.035/rated pressure,but I don't understand that a tank with lower pressure holds more liters? Example: a 95 steel tank with 2400psi(165.474bar) holds 16.40 liters.
same tank at 2650 holds 14.85 liters according to this formula. How can this be?

In the us the tanks are rated at the 10% overfil capacity (2640 vs 2400).. so one you lose the + rating it falls back to the normal working pressure so it no longer a 95 its 10% less.. at 2400 a "95" is not a 95..

cramerdn · 8th August 2007, 14:45

Quote: (Originally Posted by decoweenie)

For example, there are 7L with 200 bar tanks, and also 7L with 223 bar tanks available. The external size of these 2 tanks are the same and should displace the same amount of water when submerged.

Actually the internal size is the same and they should hold the same ammount of water if you filled them with water.

Not really an important distinction, but what the hey.

cramerdn · 8th August 2007, 15:07

Quote: (Originally Posted by jradomski)

Quote: (Originally Posted by decoweenie)

This is a rough calculation...

Convert cf into free liters using: cf * 28.3 = free liters
Convert rated pressure into bar using: psi / 14.5 = bar
Convert free liter at pressure into displacement: free liter / bar = L

For example, 80cf 3200psi into Metric equivalent:

80cf * 28.3 = 2,264 free liters
3200psi / 14.5 = 220 bar
2264 free liters / 220 bar = 10 L

As said, just roughly...

except most al "80s" are actually 77.4 cuft when using air..

Aluminum 80s are 77.4 cu ft (assuming a 3000 psi fill). The "neutrally Bouyant" AL 80s are 77.4 cu ft when filled to 3300 psi, their normal fill preasure. Those two tanks have a liquid capacity of 11.11 and 10.32 liters respectivly.

Your best bet is to scour through tank specification pages unit you find the actual liquid capacity for the tank. Then use that with the conversion factors above to find out the real capacity in free liters or cu ft, which ever way your bread is buttered.

Also you will need that real capacity to acuratly calculate SAC rates, otherwise the preasue used while doing the test is meaningless.

8th August 2007, 03:45	#11 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,510	Re: Conversion of Cylinder sizes Quote: (Originally Posted by 2002scubasteve) How can this be? Since you divide by a higher pressure, obviously you get a lower displacement L. As the Imperial unit gives the rated capacity (in 95 cf, for example) at certain rated pressure. They go hand-in-hand and must be used together. The moment you raise the pressure, the rated capacity is no longer the same (at 95 cf). It should increased. In Metric unit, the L is the equivalent water displacement of the tank. So multiplying by pressure gives you the internal gas capacity. For example, there are 7L with 200 bar tanks, and also 7L with 223 bar tanks available. The external size of these 2 tanks are the same and should displace the same amount of water when submerged. __________________ "...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..." - Rebreather World PM
(Offline)

8th August 2007, 04:18	#12 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 2,849	Re: Conversion of Cylinder sizes Quote: (Originally Posted by decoweenie) This is a rough calculation... Convert cf into free liters using: *cf 28.3 = free liters Convert rated pressure into bar using: psi / 14.5 = bar Convert free liter at pressure into displacement: free liter / bar = L** For example, 80cf 3200psi into Metric equivalent: 80cf * 28.3 = 2,264 free liters 3200psi / 14.5 = 220 bar 2264 free liters / 220 bar = 10 L As said, just roughly... except most al "80s" are actually 77.4 cuft when using air.. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.
(Online)

8th August 2007, 04:23	#13 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 2,849	Re: Conversion of Cylinder sizes Quote: (Originally Posted by 2002scubasteve) I have used the conversion formula given here cuFT/0.035/rated pressure,but I don't understand that a tank with lower pressure holds more liters? Example: a 95 steel tank with 2400psi(165.474bar) holds 16.40 liters. same tank at 2650 holds 14.85 liters according to this formula. How can this be? In the us the tanks are rated at the 10% overfil capacity (2640 vs 2400).. so one you lose the + rating it falls back to the normal working pressure so it no longer a 95 its 10% less.. at 2400 a "95" is not a 95.. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.
(Online)

8th August 2007, 14:45	#14 (permalink)
cramerdn Obey my dog! Current Rebreather/s: Evolution Dolphin Other Rebreather/s: Dolphin Join Date: Dec 2006 Location: Townsville QLD Posts: 511	Re: Conversion of Cylinder sizes Quote: (Originally Posted by decoweenie) For example, there are 7L with 200 bar tanks, and also 7L with 223 bar tanks available. The external size of these 2 tanks are the same and should displace the same amount of water when submerged. Actually the internal size is the same and they should hold the same ammount of water if you filled them with water. Not really an important distinction, but what the hey. __________________ "Its better to live one day as a tiger than an entire life as a worm." "But who's ever heard of a worm skin rug?"
(Offline)

8th August 2007, 15:07	#15 (permalink)
cramerdn Obey my dog! Current Rebreather/s: Evolution Dolphin Other Rebreather/s: Dolphin Join Date: Dec 2006 Location: Townsville QLD Posts: 511	Re: Conversion of Cylinder sizes Quote: (Originally Posted by jradomski) Quote: (Originally Posted by decoweenie) This is a rough calculation... Convert cf into free liters using: *cf 28.3 = free liters Convert rated pressure into bar using: psi / 14.5 = bar Convert free liter at pressure into displacement: free liter / bar = L** For example, 80cf 3200psi into Metric equivalent: 80cf * 28.3 = 2,264 free liters 3200psi / 14.5 = 220 bar 2264 free liters / 220 bar = 10 L As said, just roughly... except most al "80s" are actually 77.4 cuft when using air.. Aluminum 80s are 77.4 cu ft (assuming a 3000 psi fill). The "neutrally Bouyant" AL 80s are 77.4 cu ft when filled to 3300 psi, their normal fill preasure. Those two tanks have a liquid capacity of 11.11 and 10.32 liters respectivly. Your best bet is to scour through tank specification pages unit you find the actual liquid capacity for the tank. Then use that with the conversion factors above to find out the real capacity in free liters or cu ft, which ever way your bread is buttered. Also you will need that real capacity to acuratly calculate SAC rates, otherwise the preasue used while doing the test is meaningless. __________________ "Its better to live one day as a tiger than an entire life as a worm." "But who's ever heard of a worm skin rug?"
(Offline)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode