Whats a good fill?

[Jeff Pack]

With my plus rated tanks, (lp95's) lately at my favorite LDS, I seem to getting about 2400psi after a fill.

When I had tanks filled up in Seattle, they came back at 2600.

So what should I expect a tank to come back at? Cuz 200 psi on an LP tank is about 2 cu ft of air.

[mz53480]

With my plus rated tanks, (lp95's) lately at my favorite LDS, I seem to getting about 2400psi after a fill.
When I had tanks filled up in Seattle, they came back at 2600.
So what should I expect a tank to come back at? Cuz 200 psi on an LP tank is about 2 cu ft of air.

I would think ~2600 would be appropriate. Do they know your expectations and that the tanks are + rated?

[Mattleycrue76]

A good fill is one that has you looking at the pressure gauge, doing a double take, and then tip toeing to your car and laying the tanks in your trunk as if they were full of TNT

[diverden]

My definition of a good fill is when you get in the water you're at the rated pressure. Of course this would mean that at room temperature they are probably over-filled by around 200-400 psi. That would require over-filling by roughly 400-600 psi. It really depends if the shop tops off after the tanks cool or going a bit over. So, it depends on the shop and who is filling and how they feel about a bit of an over-fill. I was kind of sick of worrying about it so just kept getting bigger tanks and eventually going to doubles.

[LCF]

Well, the saying in cave country is that your dive is over when your tanks are full . . .

But in reality, if my tanks are + rated, I'd expect a 2640 fill at room temperature. If you are gauging them at home in a garage or back yard, you've lost a couple hundred psi from temperature drop, this time of year.

[Dusty2]

My take is if you get to the dive site with less than the rated pressure in your tank you just got took. This is especially true with LP tanks since they require less PSI's then standard tanks and less wear on fill equipment. The ratings on tanks are ultra conservative and marked as such to cover everyone involved in filling and servicing them as well as the end user. There are lots of bull stories used by fill station people to excuse sloppy work but they are just that. BULL. All tanks have a very generous safety margin built in by law so there is no excuse for a short fill.

Some shops will go out of there way to insure you get what you expect. Those are the shops I will return to time after time. Some shops are ultra conservative and won't see my tanks more than once or get any other business from me. Fills are not a money maker and as such tend to be low priority in most shops and relegated to the "new guy" while the boss sells gear. Most shops don't seem to grasp the fact that people tend to hang out at shops that supply good air and good fills. I put in allot time and money getting to a dive site and if my tanks are under filled when I set up then the overall cost per minute of dive time just went up dramatically and I am not a happy guy. You know I not only will not go back to that shop but I will assure that I never send a buddy that way either.

In cave country it is SOP to overfill LP tanks because peoples lives depend on it. In open water diving people are much more forgiving because they have more room in their planning and ways to exit if tanks aren't topped off.

[eliseaboo]

LP tanks were always a challenge at my old shop because they'd come in very low, and the steel tanks seemed to heat up faster than the AL. I always thought this seemed strange (wouldn't steel, as a better conductor than AL, be better at conducting the heat away? Maybe it holds the heat better?) I usually had to fill LP steels twice, and HPs sometimes three times. If you have a plus rating and you're in a new place, point it out. If the "new guy" is filling it s/he might not know yet. Also, if you are at a shop you aren't yet familiar with check your tank before you leave. If they have a problem with you checking, or won't top it off if it is low, then find another shop.

[lamont]

3800 psi fills in Al80s kind of freak me out a bit.

overfilled LP72s also would freak me out.

anything over 3800 psi is also a bit worrisome.

[Dusty2]

+1 on the 3800 psi al80's

I won't go above 3200 on aluminum tanks.

3800 on HP steel is prefect for me. In the winter especially.

In cave country overfilled LP72 doubles is the norm!

[BASSMAN]

3800 psi fills in Al80s kind of freak me out a bit.

overfilled LP72s also would freak me out.

anything over 3800 psi is also a bit worrisome.

Wow! And I thought a LP tank to 3000 psi was good!

[Nwbrewer]

I always thought this seemed strange (wouldn't steel, as a better conductor than AL, be better at conducting the heat away? Maybe it holds the heat better?) I usually had to fill LP steels twice, and HPs sometimes three times. If you have a plus rating and you're in a new place, point it out.

Aluminum is a far better thermal conductor than Steel, 120-180W/(m*K) vs 12-45W/(m*K).

For me an Aluminum fills of +/-100psi is fine, for my steels I'm pretty happy when it's at rated pressure when I hit the dive site. Of course I'm usually hitting the surface with plenty of gas, so I don't sweat it too much. I always gauge my tanks at the shop. If it's a little light and I need all the gas for the planned dive I just ask them to top it off. No one has ever complained.

[Jeff Pack]

I just checked my last fills, and 2 of the 3 were 2560 at room temp.(68)

So to really check these, you need to check at room temp?

[LCF]

Well, IIRC, the rules say that tanks are to be filled to the rated pressure at 70 degrees Fahrenheit. So if you check your pressure in a 50 degree garage, it's always going to be below the rated pressure, if the shop is following the rules.

Just to correct one thing: Cave country dive shops don't overfill tanks because people's lives depend on it. A cave diver plans the amount of penetration into the cave that he can safely do on the gas that he has. Cave country shops overfill tanks because cave divers want to do longer dives than they can do on tanks filled to the rated pressure. In MX, where aluminum tanks are the rule, tanks are not overfilled.

[Nwbrewer]

I just checked my last fills, and 2 of the 3 were 2560 at room temp.(68)

So to really check these, you need to check at room temp?

I believe you are over-thinking this one. If 80psi is going to make or break your dive, consider a bigger tank.

[spatman]

I just checked my last fills, and 2 of the 3 were 2560 at room temp.(68)

Also keep in mind that there often is a 100-200 psi discrepancy between gauges. Close enough is usually good enough.

[cardiver]

I just checked my last fills, and 2 of the 3 were 2560 at room temp.(68)

Also keep in mind that there often is a 100-200 psi discrepancy between gauges. Close enough is usually good enough.

TWSS

[spatman]

I just checked my last fills, and 2 of the 3 were 2560 at room temp.(68)

Also keep in mind that there often is a 100-200 psi discrepancy between gauges. Close enough is usually good enough.

TWSS

you need to start dating women with higher standards, ron.

[CaptnJack]

Its pretty easy to get "rated pressure at room temp" in a LP tank. The problem I suspect is lowly shop employees who don't actually know how hot the gas is relative to the rate of fill and the resulting pressure drop. At some shops I know they are filling fast enough that they need to fill that lp tank to 3100 so that it'll cool to 2640. Vs. If they filled much much slower they'd only need to hit 2800 to cool to 2640. There are common misunderstandings about how much or even if you can fill a tank beyond rated pressure (legally). The answer is yes you can as long as its at rated pressure when the gas inside is at 70F.

Don't get distracted by the discussions about "cave fills" and whether you should or can expect your shop to deliver more than 2640 at 70F (you can't).

I would just mention to your shop that your tanks are cooling to quite a bit less than their current + rated pressure and to please fill them slower or overfill them more to compensate for that drop in pressure upon cooling better.

[diverden]

I just checked my last fills, and 2 of the 3 were 2560 at room temp.(68)

So to really check these, you need to check at room temp?

I believe you are over-thinking this one. If 80psi is going to make or break your dive, consider a bigger tank.

Like you started the thread with, ±2 cubic feet (roughly 2%) shouldn't really alter your dive planning. HOWEVER, if you pay $10-12 for a cylinder of air it can be frustrating if you're consistently short. If you want a "good fill" tell them what you want. Also, you can browse the store or have some dive shop chit-chat while your tank cools and you can ask them to top it off, and/or check the pressure before you leave.

[Bric Martin]

I have found that if the fills are low and you ask the shop to top them off that most shops will do this. I showed up at a dive site once with my tanks 2/3 full, the shop had mistaken my tanks for LP. I now check the tanks pressure and o2 before I leave the shop. Most times my tanks are full or slightly over, but if they are within 200 psi I don't sweat it.

[Jeff Pack]

Thx guys, I just wanted to know how to accurately check, so it appears, check at room temp.

If I'm at 2600(plus or minus a few) don't sweat it.

But I will let them know my expectations next time.

[Dusty2]

My first rule is always leave your tanks over night, chances are if they are rushed you won't get a good fill and it's always better to check O2 after the mix has had time to settle, second show up at the shop with your own pressure gauge and O2 analyzer. This usually is enough to get the message across that you expect good fills and that you are serious about what you breath and pay for without allot of need for conversation or bull.

[airsix]

Put this on your Christmas list.
I showed up to an important dive with an empty bottle once. I never pick up bottles without this in hand now.

[Dusty2]

Put this on your Christmas list.
I showed up to an important dive with an empty bottle once. I never pick up bottles without this in hand now.

+1 never empty but way to low to complete the dive as planed.

[kagey747]

A good fill is the one you are happy with. I have yet to feel cheated because I tell the shop what I expect and always check the tank with MY gauge before paying... any discrepancies are corrected before I leave. I have never had a fill station not want to give me what I ask for, as long as I let them know when I drop it off (of course, I've never asked for 3800psi in an AL80), although I have found short fills a couple of times, they were fixed on the spot.