Please expand upon this statement.
Roak
tank filling theory...e.g. getting the pressure right
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Roak
In So Cal, or at least in the LDS that I have been in they all fill tanks in a water tank. It allows the operator to get more volume into a cyllinder at the time of filling. I dont really think that 1 or 2 hundred lbs will make much differance to the average sport diver in contrast to a tech diver who might be making penetrations into an overhead environment. I dont use aluminum tanks any more but they were always filled in a cooling tank also. Most all of the dive boats in this area re-fill on deck in the open air and the pressure commonly drops around 250-350 lbs after you hit the water. I use a low pressure steel as it is easiest to get a slight overfill on a boat rather than a short fill for a 3000 plus lb rated tank. I have done some deep jumps and also some wrecks with penetration, thats the only time I am really concerned with getting the last drop as it were. Any of the later dives I always take a completely redundant air supply and its also filled to the brim-so to speak.
Dive safe....the best workout for diving, is diving.
Dive safe....the best workout for diving, is diving.
FredT
Guest
Partially correct.
The working pressure is rated at 70°F. A tank may be filled to the point that it will cool to rated pressure at 70°F. This is the same pressure the tank woud be if the tank was filled to rated pressure at 70°F and then setting the tank out on deck in the tropical sun.
The energy transfer (heat) created when a tank is filled is constant for the same PSI/volume added to the tank. The differences to the apparent heat of filling between Al/Steel and fast/slow is the thermal mass of the tank and the rate of fill allows cooling by radiation and convection during the fill. An Al tank has 3 times as much metal to absorb the heat when compared to a steel tank. A fast dry fill does not allow the tank to radiate much heat during the fill process. Places that fill lots of tanks often use refrigerated water to cool them during the fill so they can run more tanks through the fill station each day by increasing the fill rate. A "water fill" requires great care with the fill whips to prevent water from entering the tank if a whip is accidentally dtropped in the tank, or the valve is momentarily submerged before the whip is firmly attached and pressurized.
In any case if the tank is too hot to rest it on a bare shoulder immediately after a fill, slow the fill down!
Ok, Roak asked me to expand, but I think FREDT summed it up pretty well.
The issue of filling tanks in water is a sticky one. Some people/agencies believe that you should never fill in water, because it has minimal benefit, and it forces water into the cylinder.
They may be right, however, what we have found is that if you do not drop the whip or the tank valve below the surface of the water, there is NO chance of water going into the cylinders.
The way we have our tub set up, the tanks slide in, and just lean against the side, so the whole tank is NOT submerged. just the bottom half or so of it. The whips NEVER get wet, nor are they ever SUBMERGED.
Steel tanks heat up during a fill. Alot more than aluminum, which tends to dissipate the heat much better than steel. Steel tanks need to be filled slower, and cooled off in a water tub in order to ensure a good fill.
I stated earlier a 600 psi per minute fill. That is kinda fast, and I think steels we do more like 300 psi per minute.
Also, service pressure is measured at 70 deg f. I left that part out, thanks for that FREDT.
We actually never have a problem giving good fills because of the slow fill rate and out water tub. People actually thank us on a regular basis for the good fills...
I think people are used to getting shorted a couple hundred pounds on a fill. You really need to be patient, and let it take more time, and you will get a good fill.
I also fill all my own tanks, so I never have a problem with getting a good fill, unless I am in a rush to get to the pool, and then my tanks get a short fill. But, in a pool, its no big deal. I like a real FULL fill for all open water dives however. I dont like getting my tanks filled somewhere else...
Roak, did that help???
The issue of filling tanks in water is a sticky one. Some people/agencies believe that you should never fill in water, because it has minimal benefit, and it forces water into the cylinder.
They may be right, however, what we have found is that if you do not drop the whip or the tank valve below the surface of the water, there is NO chance of water going into the cylinders.
The way we have our tub set up, the tanks slide in, and just lean against the side, so the whole tank is NOT submerged. just the bottom half or so of it. The whips NEVER get wet, nor are they ever SUBMERGED.
Steel tanks heat up during a fill. Alot more than aluminum, which tends to dissipate the heat much better than steel. Steel tanks need to be filled slower, and cooled off in a water tub in order to ensure a good fill.
I stated earlier a 600 psi per minute fill. That is kinda fast, and I think steels we do more like 300 psi per minute.
Also, service pressure is measured at 70 deg f. I left that part out, thanks for that FREDT.
We actually never have a problem giving good fills because of the slow fill rate and out water tub. People actually thank us on a regular basis for the good fills...
I think people are used to getting shorted a couple hundred pounds on a fill. You really need to be patient, and let it take more time, and you will get a good fill.
I also fill all my own tanks, so I never have a problem with getting a good fill, unless I am in a rush to get to the pool, and then my tanks get a short fill. But, in a pool, its no big deal. I like a real FULL fill for all open water dives however. I dont like getting my tanks filled somewhere else...
Roak, did that help???
In the 70's in or near Daytona Beach there was a shop that had an old soda machine. For you older folks, remember the ones that looked like an ice cream freezer full of circulating water w/ the soda bottles sitting in the water? They had one of these w/ which they set the tanks in to fill them. The water was right at freezing. The claim was that your fills went up when you left the shop, not down. I have no memory of how well this worked on our steel 71.2's but we thought it was a neat idea at the time. Never seen it anywhere since (chilled).
so far, both my own LDS, and a shop that was near todays dive site "shorted" me 300 psi, and put 3000 into my 3300 psi tank, even though both places acknowledged verbally that they were aware that my tank was rated at 3300psi (at 70F).
I'm stumped why this happened....My dive buddy today suggested that they might have taken my tank off when it hit 3000 without thinking, since most AL80's are rated to 3000.....
I may need to be more persistent....Any other ideas/suggestions to get the extra 300 psi?
Many thanks!
Sean
I'm stumped why this happened....My dive buddy today suggested that they might have taken my tank off when it hit 3000 without thinking, since most AL80's are rated to 3000.....
I may need to be more persistent....Any other ideas/suggestions to get the extra 300 psi?
Many thanks!
Sean
Ontario Diver
Guest
I think your buddy is right. Take some Duct tape and write on it "FILL TO 3300 PSI" and stick it to the tank. Then explain it to the fill jockey....
scubafanatic
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....you might have to get sneaky.......install a DIN tank valve on it......chances are they'll go ahead and assume it's a HP steel 3500 psi tank and give you that much......which might cool down to the 'target' 3200-3300 psi you're after.
( I use modular valves, DIN with screw-in yoke inserts on my LP steels.....however, even if I don't remove the insert and let them fill it as a yoke valve, they still usually fill it such that I end up with 3000 psi 'cold'.......however, I've taken the time to find 'cooperative' dive shops that understand LP steels are perfectly fine with a bit of overfill)
( I use modular valves, DIN with screw-in yoke inserts on my LP steels.....however, even if I don't remove the insert and let them fill it as a yoke valve, they still usually fill it such that I end up with 3000 psi 'cold'.......however, I've taken the time to find 'cooperative' dive shops that understand LP steels are perfectly fine with a bit of overfill)
sheck33
Contributor
True only when the process is adiabatic.
In general dT/dt is proportional to dP/dt, the faster i try to increase the pressure the hotter the tank will end up being.
This is similar to the tank valve getting very cold when you open it all the way and let the gas out very quickly, this DOES happen adiabatically
anybody correct me if i am wrong
plsdiver4377
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I have the same problem since 4 of my tanks are 3300's. I have found that I have to remind them whenever I get them filled, and I still end up short due to cooling. One shop will usually overfill by 200 to help with this problem though.:mean:
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