Why US bottle sizes are confusing

Jump to latest Follow Reply
Chickenthief

Chickenthief

Member
Aug 16, 2019
820
151
Intoxicated, Denmark
So you mention a 90cui bottle but thats the true volume of the bottle ie. 1.47liter



Then you mention a 110cft bottle but not at what pressure that is the volume of air, most often we have to guess that it's 4500psi and in the end a (110ft=3100liters at 4500psi~310bar = 10liter).



The real confusion starts when you fling bottle sizes in minutes!

As all y'all state tank sizes rated in minutes is that total volume or - the safety factor?

http://breatheair.com/2017/11/09/scba-cylinder-breathing-duration-calculation/



Without ie. true tank volume

1min = 40liters

30min = 1200liter/300bar = 4liter

45min = 1800liter/300bar = 6liter

60min = 2400liter/300bar = 8liter

75min = 3000liter/300bar = 10liter

90min = 3600liter/300bar = 12liter





With safety volune (ie. -50bar)

1min = 40liters



30min = 1200liter/300bar (50bar x 4liter =200liter ie 0.66liter) = 3.33liter

45min = 1800liter/300bar (50bar x 6 liter=300liter ie 1.00liter) = 5liter

60min = 2400liter/300bar (50bar x 8liter=400liter ie 1.33liter) = 6.67liter

75min = 3000liter/300bar (50bar x 10liter=500liter ie 1.67liter) = 8.33liter

90min = 3600liter/300bar /50bar x 12liter = 600liter ie 2.00liter) = 10liter





Yet they are the exact same bottles!!!





A 610cui tank is a 110cft tank and also a 90min tank (-SV) and lastly a 10liter tank. See?





Not trying to bash anyone but sometimes it confusing and hard to give proper help for a foringer ;-)
 
Haha yeah it's equally hard trying to make sense of it the other direction too LOL. I know what a 90 min Scott pack is, I've worn them. I have a 98 cu ft bottle but could not find anything to figure out what the heck they would be in liters.

Was chatting with friends about the metric system, saying how it's a lot easier when doing a bunch of calculations if you have equipment that works with metric, drill bits, measuring devices etc. But the tricky part is trying to visualize what 4cm is when you aren't used to it, where "oh it's about four Bic lighters long" is easier as in my mind I have that programmed in my head already.

I don't know how many stone I weigh or how many hands high I am, but I know a guy that is 6'5" tall is tall. :).
 
Upvote 0
The Canadians got it even worse!

They sat right between two chairs.

Canadian system of measurements.1640960224.jpg

 
Upvote 0
Since i have derailed this thread myself let me add:

Know why there was left hand "driving" and why we switched to right?

From ancient times we walked/rode the left side of the road so we could meet our opponent sword hand (right) to sword hand.

The French peasants got tired of being hit by aristocrats horse carriages from the back walking the side of the road and simply switched sides so they could see carriages beforehand and avoid.

The French revolution in 1789 meant changing all established/aristocratic with new. Thus all new measurements and they even implemented a 10hour/100min/100sec day. https://en.wikipedia.org/wiki/Decimal_time

That went off like a fart in a diving helmet, but weight, length metric standards stayed. And an official switch to right hand driving.

https://en.wikipedia.org/wiki/History_of_the_metric_system
 
Upvote 0
Haha yeah it's equally hard trying to make sense of it the other direction too LOL. I know what a 90 min Scott pack is, I've worn them. I have a 98 cu ft bottle but could not find anything to figure out what the heck they would be in liters.

Was chatting with friends about the metric system, saying how it's a lot easier when doing a bunch of calculations if you have equipment that works with metric, drill bits, measuring devices etc. But the tricky part is trying to visualize what 4cm is when you aren't used to it, where "oh it's about four Bic lighters long" is easier as in my mind I have that programmed in my head already.

I don't know how many stone I weigh or how many hands high I am, but I know a guy that is 6'5" tall is tall. :).
Click to expand...

It is even worse than you describe. Very often a bottle size is described or a compressor volume is stated per minute at a volume pressure other than max or atmosphere, which is even more confusing. Of course the pressure used for this number is rarely ever stated. However, it is common to use the magic number of 8 bar, as it is often used to rate low pressure air equipment and tools...........jus sayin!
 
Upvote 0
Its easy to see why tanks are marketed by air CAPACITY rather than liquid volume in applications that use low pressure air. Ex: Firefighter or SCUBA. If the tanks are always filled to max and you are able to use the air down to near zero, then the air CAPACITY is a direct indicator of the usage you will get and makes it easy to do comparisons for the non-technical.

Airgun use? Too many variables. Please, just show me the liquid volume in liters and max fill pressure!



Metric system is pretty solid, but has a few crummy units. I heard Elon Musk call one out, but can't remember what one. My complaint is the glaring hole in length measurement related to the imperial FOOT. The meter is a convenient base because you can scale up or down by 3 decimal places and go from millimeters to kilometers, but the meter itself is not a very good unit for describing things people interact with every day (how tall a person is, how big that room is, etc). This could probably be mitigated by using the decimeter more, but I think I'm the only one who likes that.




 
Upvote 0
While not nearly as necessary with airguns as it is with diving, a bit of reading about the "Ideal Gas Law Deviation" might be of interest.



DW
Click to expand...

I am really confused now. I am fully informed on both basic adiabatics and the gas laws and I see little value in their reference to bottle volume and their max rated pressure. Please elaborate?
 
Upvote 0
While not nearly as necessary with airguns as it is with diving, a bit of reading about the "Ideal Gas Law Deviation" might be of interest.



DW
Click to expand...

I am really confused now. I am fully informed on both basic adiabatics and the gas laws and I see little value in their reference to bottle volume and their max rated pressure. Please elaborate?
Click to expand...

It has to do with gasses not being as compressible at higher pressures (and lower temps). If memory serves, I think that the differences were negligible until around the 4,000 psi stage, but I could be mis-remembering. At higher pressures, such as we dealt with in steel tanks that were "cave" filled, it made enough difference that it was possible to have to get into your reserve gas (best case) due to calculations and run times/gas usage being skewed.



https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/deviation5.html



DW
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu