Re: How Was Dive w/Greg II

Grumman-581 wrote:
Checked my computer... First dive was 140 for 28, second dive was 133
for 25... Both were to the sand on the west side of the ship...

Oh, forgot to add -- 1st dive was with 2 AL80s only filled to 2000 psi,
2nd dive only used a single steel 72 for the dive and the deco...

Had planned to get them all refilled yesterday, but Fill Express had
closed early... Went over to Splashdown to get them filled up, but
parking is crap over there and I didn't fill like hauling 7 tanks a
block or so from the nearest parking spot, so I decided to pass on
them... Got them filled up at Fill Express today... The tank filler
dude had a problem calculating the gas that went into the 4
steel-72s... He came up with this figure that didn't sound at all
right... I calculated it myself and to get his figure, all the 72s
would have had to be pretty damn close to empty, which some of them
weren't... Their procedure appears to be to put like capacity tanks
together and equalize their pressures and then fill all of them in
parallel to the same pressure... So, for my 4 steel-72s, they equalized
at 1700 psi (one or two of them were damn close to full apparently)...
His first calculation came up with something like 237 cu-ft of gas
added to them... That didn't sound exactly right since they would have
only held 288 cu-ft if they were all completely empty... After I told
him that it didn't sound right, he came back with the right number --
around 75 cu-ft... Surprisingly, they don't have a computer program to
help them with this... They just expect the fill guy to be able to
calculate it with a simple calculator... Yeah, I would like to think
that someone with at least a high school education should be able to
calculate it, but it leaves room for error (obviously)...

Since they charge by the cu-ft, I had originally thought that perhaps
they had some sort of meter that measured the cu-ft of gas that was
pumped into the tanks... Turns out that they just use pressure
differential to calculate the cu-ft...

The calculation is probably something like this:
(([ending pressure] - [starting pressure]) / [rated pressure]) * [rated
volume at rated max pressure]

As a side note, most (if not all) of my steel-72s were older than the
fill guy... Starting to make me feel old...

.

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