GLENFWB
Contributor
Does anyone have a link to a site that lists the cubic foot capacities for an LP 108 at various pressures? Also, anyone know of any good discussions of gas matching on the web?
Gas Matching with LP 108's
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pressure/2640*108=cubic feet
Tank factor for a 108 is 4.1. That means you have 4.1 cf per 100psi.
4.1 x 26.4 (2640/100) = 108cf
4.1 x 30 = 123cf
4.1 x 36 = 147.6cf
It's part of my cavern/cave courses, as well as my Advanced Nitrox/Deco courses, but I'll be more than happy to discuss gas matching in more detail on Friday.
4.1 x 26.4 (2640/100) = 108cf
4.1 x 30 = 123cf
4.1 x 36 = 147.6cf
It's part of my cavern/cave courses, as well as my Advanced Nitrox/Deco courses, but I'll be more than happy to discuss gas matching in more detail on Friday.
Yes, you should definitely cover this in your intro course. Jim Wyatt has a good explanation and a chart on his site:
Cave Dive Florida Gas Matching Table & Example
Cave Dive Florida Gas Matching Table & Example
I found for me, the best way to understand was to actually put the calculations into a worksheet. The attached worksheet will allow you to input the values for tank size, rated pressure and actual pressure and it will do the gas management calculations. I also did the same for nitrox calculations in the sheet. This is nothing earth shattering, but it is just how I remember stuff, by working through the problem of setting up the formulas.
OP
GLENFWB
Contributor
Thanks Rob. Josh and I have been trying to work through gas matching with his HP 100's and LP 108's. I am trying to get a handle on as many things as I can before taking Intro. At my age I try to minimize information overload!
OP
GLENFWB
Contributor
ShagMan
Contributor
I took cavern with Rob and we did go over gas matching, but I haven't been keeping a few of the skills in practice (gas matching, s-drills and advanced signaling skills).
I've been more focused on good bouyancy, getting my gear settled, reel work, things like that.
Glen and I are trying our best to brush up on our needed skills for Intro.
Subscribing to this thread for the good info!
I've been more focused on good bouyancy, getting my gear settled, reel work, things like that.
Glen and I are trying our best to brush up on our needed skills for Intro.
Subscribing to this thread for the good info!
runawaylobster
Guest
I saw some good links in this thread, Nice spreadsheet...
mine always work but they never look nice too.
Just a quick reminder though that you can do a quick check prior
to entering the water but you do need to do your final gas calculations
(Critical air supply and turn pressures) after you have done your
safety checks, gas shares etc.
Why? because a) you will use some
gas doing all that stuff
and also b) If there is a differential between water
temperature and air temperature your available PSI will change especially
with the large volumes of gas we cave divers carry.
For a Florida example, on one of those cold wintry mornings your gas will expand
when you enter the nice toasty spring water (that only a few months ago
felt cold to you) your gauge will read higher after a short while, jeez you might
even get an extra 100 psi. Of course the more scary scenario is that the colder
spring water in the summer causes your gas to contract and your carefully calculated
1/3 is actually more than the true volume you end up with!! now that's scary.
LL
mine always work but they never look nice too.
Just a quick reminder though that you can do a quick check prior
to entering the water but you do need to do your final gas calculations
(Critical air supply and turn pressures) after you have done your
safety checks, gas shares etc.
Why? because a) you will use some
gas doing all that stuff
and also b) If there is a differential between water
temperature and air temperature your available PSI will change especially
with the large volumes of gas we cave divers carry.
For a Florida example, on one of those cold wintry mornings your gas will expand
when you enter the nice toasty spring water (that only a few months ago
felt cold to you) your gauge will read higher after a short while, jeez you might
even get an extra 100 psi. Of course the more scary scenario is that the colder
spring water in the summer causes your gas to contract and your carefully calculated
1/3 is actually more than the true volume you end up with!! now that's scary
.LL
loquat149
Contributor
Here's a slightly modified version of a table someone posted on one of the tech forums a year or so ago that I've found useful. You can print it out, fold in half, laminate, and stick it in your wetnotes and easily perform in-water gas matching. I'd recommend running through a number of examples topside to make sure you understand how it works. After a while, you'll start to see some patterns emerge, such as what happens when a dive team uses lp85's, 95's, and 104's, etc. Also note that while not all cylinders are listed, you can add your own data or use substitutions (e.g., lp98s = lp95's, etc.).
Good luck,
Dave
Good luck,
Dave
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