Calculate tank volume?

[sunnydude]

Without naming the shop, I took my new to me LP95's to get the vis updated and filled. When I was getting rung up the clerk said, "good thing I checked, you wouldn't be very happy to find out you've only got 2600psi". I was a bit confused but then the clerk said they are at 3000psi. This would be all and good but the tanks are LP tanks! So...how much air do I have in there now? Where can I find a calculator?

[spatman]

Without naming the shop, I took my new to me LP95's to get the vis updated and filled. When I was getting rung up the clerk said, "good thing I checked, you wouldn't be very happy to find out you've only got 2600psi". I was a bit confused but then the clerk said they are at 3000psi. This would be all and good but the tanks are LP tanks! So...how much air do I have in there now? Where can I find a calculator?

95cf divided by 2640psi = roughly .036 cf/psi

so 3000psi x .036cf/psi = 108cf


yay, scuba math!

[CaptnJack]

or more simply.
95cf/26 (hundreds of psi) = 3.5 cf per 100 psi
3.5 x 30 (hundreds) = 105cf

(close enough since some would call the same tank a lp98)

[spatman]

i was just writing this when the capt posted his...


another handy way to figure out your tanks volume at any pressure is to use a tank factor of 3.6 for every 100psi on your gauge.

as illustrated above 1psi = .036 cubic feet in your tank.

so 100psi = 3.6 cubic feet

[sunnydude]

Thanks guys.

[Paulicarp]

i was just writing this when the capt posted his...


another handy way to figure out your tanks volume at any pressure is to use a tank factor of 3.6 for every 100psi on your gauge.

as illustrated above 1psi = .036 cubic feet in your tank.

so 100psi = 3.6 cubic feet

that only applies to tanks with this constant, right? it would be different for an AL80, or any tank with a Kt that is not the same.

[Pez7378]

Just calculate the Tank Factor for any given tank as Richard showed.

LP 98/2640x100=TF 3.7

Al 80/3000x100 = TF 2.6

Divide the CuFt capacity by the rated pressure and multiply by 100.

stupid decimal!

[spatman]

that only applies to tanks with this constant, right? it would be different for an AL80, or any tank with a Kt that is not the same.

exactly. you divide the tank's volume by its rated pressure then multiply by 100 to get the tank factor.

so to use an al80 for example (which isn't really 80 cf, btw):

77.4 cf / 3000psi x 100 = about 2.6cf per 100psi.

got 2000psi showing on your gauge?

20 x 2.6 = 52 cf in your tank.

[CaptnJack]

i was just writing this when the capt posted his...


another handy way to figure out your tanks volume at any pressure is to use a tank factor of 3.6 for every 100psi on your gauge.

as illustrated above 1psi = .036 cubic feet in your tank.

so 100psi = 3.6 cubic feet

common round numbers, cf per 100 psi (derived from cf/working psi in 100s)
al80 = 2.5
hp80 = 2.25
lp85/hp100 = 3
lp95/hp119/hp120 = 3.5
lp108/hp130 =4

For me using stuff like 2.5 vs 2.6 adds up to 3cf in an AL80, no big deal and trivial compared to gauge variation anyway. These numbers a little easier to work in your head.

[Paulicarp]

is it safe to overfill that tank to 3000psi, or did that shop make a dangerous mistake?

I've read that some tanks marked with a + are safe to overfill by 10% why is that true for some tanks and not others?

[sunnydude]

The tank is + rated over the 2400, so the 2640 is the full rating. I am going to let some of the air out of the tanks to make sure I don't have a problem.

My Steel 88 that I bought off this board was + rated but when I had the Hydro updated I didn't ask them to do that rating. It would have taken it from 3000 to 3300. I have been tempted to have them re Hydro so then I have all three ~ 95's

[Pez7378]

is it safe to overfill that tank to 3000psi, or did that shop make a dangerous mistake?

I've read that some tanks marked with a + are safe to overfill by 10% why is that true for some tanks and not others?

I've seen tanks filled to 3900 psi before. I'm not too keen on the Hydro test, but I bet it's way above and beyond anything the shops can do to them. Sean, they're fine.

[spatman]

The tank is + rated over the 2400, so the 2640 is the full rating. I am going to let some of the air out of the tanks to make sure I don't have a problem.

My Steel 88 that I bought off this board was + rated but when I had the Hydro updated I didn't ask them to do that rating. It would have taken it from 3000 to 3300. I have been tempted to have them re Hydro so then I have all three ~ 95's

don't let the air out, dude, just go dive it. the tank can handle overfilling once in a while.

the plus rating is only valid for the duration of its 1st hydro. once it's rehydro'd most places won't fill it to it's + rating.

[sunnydude]

the plus rating is only valid for the duration of its 1st hydro. once it's rehydro'd most places won't fill it to it's + rating.

On the 88 there are at least 3 hydros that show the + rating.

[BDub]

he plus rating is only valid for the duration of its 1st hydro. once it's rehydro'd most places won't fill it to it's + rating.

The hydro facility will not test it with the + rating unless you specifically request it. You just have to remember to request it.

As far as your tanks, Sean. I've had my double lp95's pumped up to 3700 before. Just dive em.

[sunnydude]

As far as your tanks, Sunny. I've had my double lp95's pumped up to 3700 before. Just dive em.

Pez...you see that? I am packing 105cu feet for Monday!

[spatman]

The tank is + rated over the 2400, so the 2640 is the full rating. I am going to let some of the air out of the tanks to make sure I don't have a problem.

one thing to keep in mind is that even though the plus rating is 2640psi, that's still the number they use when calculating cf. so when your lp95 is "full" at 2400psi, you actually have a less than 95 cubic feet in your tank.

[Pez7378]

Since were on the topic, and well, most of us involved in this conversation don't have much experience with this stuff, I'd like to hear some stories of tanks gone bad. Bob, CaptJack, Matthew, Romer, Steding, BDub, DMitchell? Anyone? What are some stories that PSI is telling? What have you witnessed?

[spatman]

he plus rating is only valid for the duration of its 1st hydro. once it's rehydro'd most places won't fill it to it's + rating.

The hydro facility will not test it with the + rating unless you specifically request it. You just have to remember to request it.

really? well, color me informed.

[dsteding]

As far as your tanks, Sean. I've had my double lp95's pumped up to 3700 before. Just dive em.

You know they are too full when champagne bubbles are coming out of the burst disc . . .

[CaptnJack]

is it safe to overfill that tank to 3000psi, or did that shop make a dangerous mistake?

I've read that some tanks marked with a + are safe to overfill by 10% why is that true for some tanks and not others?

I have some 3AA steel gas supply tanks in my garage that are 60+ yrs old. Although not officially legal, they can take generous overfills (more than 2400+10%) without any real effects. Long long term (25+yrs) they may fail hydro slightly sooner. But if those fills shorten the life from 80yrs to 30yrs who cares.

[Stu]

Without naming the shop, I took my new to me LP95's to get the vis updated and filled. When I was getting rung up the clerk said, "good thing I checked, you wouldn't be very happy to find out you've only got 2600psi". I was a bit confused but then the clerk said they are at 3000psi. This would be all and good but the tanks are LP tanks! So...how much air do I have in there now? Where can I find a calculator?

Wish I got fills like this. Enjoy the extra BT.

[BDub]

As far as your tanks, Sean. I've had my double lp95's pumped up to 3700 before. Just dive em.

You know they are too full when champagne bubbles are coming out of the burst disc . . .

Minor details

[Pez7378]

For me using stuff like 2.5 vs 2.6 adds up to 3cf in an AL80, no big deal and trivial compared to gauge variation anyway. These numbers a little easier to work in your head.

This is helpful for me. I generally use a calculator for all numbers that add up to more than 1 so any little trick that makes it easier to add is great!

[dsteding]

As far as your tanks, Sean. I've had my double lp95's pumped up to 3700 before. Just dive em.

You know they are too full when champagne bubbles are coming out of the burst disc . . .

Minor details

Breathe it down, the bubbles go away . . .