Transfill calculations?

[HenrikBP]

I've been trying to do some transfill calculations to plan an upcoming trip and wanted to run my numbers by you guys. Does this look like I got it right?

I'll be diving Catalina AL80 doubles: Total volume: 154 cu.ft. working pressure: 3000 PSI => Tank factor = 5.13 cu.ft./100 PSI

I'll transfill from a HP120: Total volume: 120 cu.ft. Working pressure: 3442 PSI => Tank factor = 3.48 cu.ft./100 PSI

Figure I use 80 cu.ft. on the first dive and then transfill from a full HP120. 80 cu.ft. of gas out of the AL80 doubles leaves me with 74 cu.ft. => ending pressure = (74 cu.ft./5.13 cu.ft./100 PSI) = 1400 PSI (1442 rounded down).

Lynne posted these transfill formulas:

X*TF1 = Y*TF2 => X = (Y*TF2)/TF1
SP1 + X = SP2 - Y => Y = (SP1 + X) - SP2

X = (((SP1 + X) - SP2) * TF2)/TF1

X is pressure rise in the low tank in 100's of psi
Y is pressure drop in fuller tank in 100's of psi

TF1 is tank factor for low tank;
TF2 is tank factor for fuller tank

SP1 is starting pressure in low tank
SP2 is starting pressure in fuller tank

Running the numbers I get a pressure rise in the "low tank" i.e. the AL80 doubles of 800 PSI. That brings me to 2200 PSI or 112 cu.ft. in the doubles after the transfill.

What do you think?

Thanks,

Henrik

 

[TSandM]

Using round numbers, that's what I come up with, too. As a sanity check, the Al80's go up 800 and the 120 goes down 1400. Given the TF ratio of 5 to 3.5, that's about right.

 

[Rainer]

Yup, I get just north of 2200psi (equalization pressure).

 

[HenrikBP]

Thank you guys. It took me awhile to figure out the calculations and I appreciate you guys' confirmation.

Henrik