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Ladyvalea
10-11-2008, 00:25
Ok I'm a newbie on tank fills.. huh....I get my tank filled at my LDS I think it was to 3000psi? so I take it to CSSP and dive for about 45 mins and get the tank to 500psi ...we get out and take a rest for about 20mins and my hubby takes the tank to get refilled at the CSSP tank station
So I get ready to dive again and my new tank fill reads 2300psi something like that? I don't remember now...but is there a reason the man did not fill the tank closer to the 3000 psi ??? I Not being cheap?? Huh???

is there a rule in tank fills? to close to the end of a dive? something about being hot?? these were 80 alu tanks thanks

fire diver
10-11-2008, 02:56
Sounds like you just got a short fill. If they fill your tank too quickly, it gets hot. once the tank cools down, especially after hitting the water, it colls down and shows the real amount of fill.

When I fill my own tanks, I usually lose about 200-300 PSI, 700 is a lot. I would have asked to be toppped off before the dive.

Grin
10-11-2008, 06:43
When I pick my tanks up I always grab a pressure gauge and see what's in them. Due to the heat thing they might have 2800-3300. Usually they are right around 3000, but it's nice to know if you got a good fill(3300:smiley20:). And if it's not at 3000, just show them, and they'll be glad to bring it up to 3000 for you, right then and there.
When i first started diving I just trusted them and I ended up with situations like this one on rare occasion. It could be your tank leaked down due to a bad valve or more likely a valve not cranked off all the way, or the tank filler could have shorted you my mistake. You'll never know if you don't check when you pick your tanks up. I've rigged a new tank and then went to turn the valve on and nothing :smiley29:. It happens! And guessing is usually all you have to go on.

SynCitizen
10-11-2008, 09:19
IMO it comes down to this... You are ultimately responsible for all of your gear. Whether it's air fill, o-rings, weights locked in, gauges working, etc etc .... everything.
Sure a dive shop should fill it properly and most times they will, but mistakes happen. You can rent gear and assume everything is there and something could be missing/broken and you dont find out till your gearing up.
Leave nothing to chance when dealing with gear. In the end it doesn't even matter who's fault it is if your 100 miles away from a shop.

skdvr
10-11-2008, 10:39
One thing to condsider is that when you are diving and then getting fills. If your tanks sit for a little while outside they will get hot even before you start filling them. Then you take them to the fill station and they maybe fill a little faster than they should because there is a ton of people trying to get fills, so the tank gets extra hot, then when you get in the water they really cool down so they get fairly low. Just one of those things at a quarry when trying to do multiple dives off of one tank. What I try to do is after a fill if I am not diving for a little while I will just take the tank down to the quarry and just dunk it in the water for a few min then stick it in the shade. I will then check it just before I get rigged up and if it is really low I will have them top it off. Most of the time I just deal with the fills, unless they are really low....

Phil

fisheater
10-11-2008, 12:13
For my HP fills, I usually drop off my tank at the LDS on my way to lunch and pick it up again afterwards. That gives the LDS time to fill the tank, let it cool and top it off again.

ReefHound
10-11-2008, 13:24
People have covered the quick/hot fills aspect. In addition, they may short fill a bit if there is a line waiting. So a hot fill to 2800 might cool to 2300. One more thing is their gauges may be reading a bit high. They may think they filled it to 3100 when it was really only 2800.

Usually it's not a big deal. I love local diving but there's usually not anything so fascinating that after 60 minutes I'm thinking "if only I had 5 more minutes". Whereas if I am on a Caribbean weekend and I'm paying $1000 for six dives then I want every last minute that I deserve.

And there's the principle of it. I'll bet the fill operator wouldn't be so happy if you shorted him on the fee by a buck or two.

Crimediver
10-11-2008, 20:06
My lds usually gives me a slight overfill to allow for cooling. Once in a while I need a wee bit more and I will tell them to give me a "Hatteras Fill ".
That is a seccret code that lets the shop know that I need more air than normal and the sake of the free world hinges upon my mission not being compromised by not having enough air to fill a lift bag, etc.

Vercingetorix
10-11-2008, 22:55
I've had my tank filled at CSSP many, many times times. In this case, you got a short-fill. I know this is frustrating, given that fills are $8, which is really stiff. My tank is rated for 3300 psi; I have to point that out. You may have to point out that your AL is rated for 3000; a lot of LP steel tanks are rated for 2400. Perhaps the employee got a bit confused there.

JahJahwarrior
10-12-2008, 06:21
My lds usually gives me a slight overfill to allow for cooling. Once in a while I need a wee bit more and I will tell them to give me a "Hatteras Fill ".
That is a seccret code that lets the shop know that I need more air than normal and the sake of the free world hinges upon my mission not being compromised by not having enough air to fill a lift bag, etc.

That's kind of cool and funny at the same time :)


I am lucky to live where I live....well actually the dive shops in Orlando look at my doubles weird and I usually have to educate them on how a manifold works, and they never give me a good fill....but up there in Gainesville/High Springs Florida area, I balk if the shop calls anything under 3600 "full." :D Really it's just because I'm lazy, it's easier to remember your turn pressure if it is the same as the operating pressure of the tank... ;)

I used to have a 3300 psi aluminum tank and I almost never got good fills...people refuse to overfill aluminum much at all :( But hey always stand up to dive shops who try to push you around, know what is a good fill and make sure you get one! (especially at $8/pop!!)

cummings66
10-12-2008, 10:19
Just remember, there is an acceptable overfill for al cylinders depending on temps and such. It's not large but it's enough that when it cools you have 3000 psi in a 3000 psi cylinder.

To grossly exceed those values is irresponsible and perhaps dangerous in an AL cylinder. Keep in mind, a fill to test pressure while not dangerous does reduce the lifespan of a cylinder and at some point it will go boom. That's why test fills are done in that special device the hydro shop owns, if it goes boom it's not going to kill somebody.

For this conversation, you got a short fill by accident. Always check your cylinders to insure you have the air you need for a given dive before you leave the shop.

ReefHound
10-12-2008, 11:51
To grossly exceed those values is irresponsible and perhaps dangerous in an AL cylinder. Keep in mind, a fill to test pressure while not dangerous does reduce the lifespan of a cylinder and at some point it will go boom. That's why test fills are done in that special device the hydro shop owns, if it goes boom it's not going to kill somebody.

It's also why they use water and not gas. The cylinder just splits rather than going kaboom.

Daddy Diver
10-12-2008, 15:18
This explanation might help.

The ratio of pressure times volume divided by temperature is always the same. It is expressed mathmatically as PV/T=PV/T. To fill you cylinder, the pump takes 80 cubic ft of air at ambient temperature and pressure adn shoves it into your dive tank and into a much smaller space, thus raising the pressure and the temperature. As the air cools down back to ambient temperature, the pressure also drops. As a tank is filled, the temperature in the tank rises. If the tank is filled quickly and not allowed sufficient time to cool while filling, you wil hit 3000 psi and be "full" but hot and thus once it cools, not be completly full. The sure is to slowly fill the tank so that the heat created by the increased pressure can dissipate such that there is not sufficient heat (in excess of ambient temp) to affect the pressure inside the tank. I know I try to take 1/2 hour to fill my hihgpressure steel tanks.

I' have no knowledge in the area of overfilling tanks or exceeding their ratings, but I would not advise it as some have here.

in_cavediver
10-12-2008, 16:08
This explanation might help.

The ratio of pressure times volume divided by temperature is always the same. It is expressed mathmatically as PV/T=PV/T. To fill you cylinder, the pump takes 80 cubic ft of air at ambient temperature and pressure adn shoves it into your dive tank and into a much smaller space, thus raising the pressure and the temperature. As the air cools down back to ambient temperature, the pressure also drops. As a tank is filled, the temperature in the tank rises. If the tank is filled quickly and not allowed sufficient time to cool while filling, you wil hit 3000 psi and be "full" but hot and thus once it cools, not be completly full. The sure is to slowly fill the tank so that the heat created by the increased pressure can dissipate such that there is not sufficient heat (in excess of ambient temp) to affect the pressure inside the tank. I know I try to take 1/2 hour to fill my hihgpressure steel tanks.

I' have no knowledge in the area of overfilling tanks or exceeding their ratings, but I would not advise it as some have here.

Hey, that just the ideal gas laws. Why not play with the real gas laws with variable compressibility? You know, when the mix changes based on pressure! Oxygen/nitrogen are fairly close in compressibility but He isn't.

As for overfilling - I am cave diver so enough said on that. (so nice of them to stamp turn pressures on the tank neck though)

Crimediver
10-12-2008, 19:27
Yeah, I also have 3 or 4 3300 Al 100's that would constantly get shortchanged on fills. Then the same shop would try to put over 3000 psi in a lp 72 tank. I guess they figure it all evens out....

captain
10-12-2008, 19:44
Remember full means rated pressure at 70 degrees F. That means if it is a 90 degree day and pressure is at rated pressure, say 3000 psi, it is not full. If it is a 40 degree day and it is at rated pressure it is over filled.