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mm2002
10-24-2007, 17:56
Every time we get aluminum tanks from our LDS they are filled to 3500 psi. I know they are rated at 3000, and haven't said anything since they are comping us the tanks until ours get back from hydro, but it's always made me wonder. Is this common practice?

texdiveguy
10-24-2007, 18:03
Every time we get aluminum tanks from our LDS they are filled to 3500 psi. I know they are rated at 3000, and haven't said anything since they are comping us the tanks until ours get back from hydro, but it's always made me wonder. Is this common practice?

No.....Its not a good practice to overfill Al. scuba cylinders.

Jipps
10-24-2007, 18:28
no it is not common. Al cylinders are not good to overfill, a few hundered pounds isnt too bad, but 3500 is way over.

mm2002
10-24-2007, 19:17
Kinda what I figured. What keeps going through my mind is that they could be endangering our lives (and quite frankly that pisses me off a bit).
What's difficult is being a dive newb, and trying to talk with the LDS owner about it, who has 25 years experience and every cert imaginable. What really got me thinking was last weekend when I rented a steel HP100, and my wife got the usual AL63. They both were filled to 3500. Being new to this, I still look at our primary regs, and stamped right there is 3000psi, not to mention the same rating on the AL tank. I need to confront him about this, but not sure how. Sure, if I was an experienced diver with 1000 dives I may go chew his ass out, but we're talking a freshly certified dude like me with 16 dives.

skdvr
10-24-2007, 21:05
I understand that could be a tough call to confront someone with both of you being in the positions you are in. What I would probably do is just ask a question about it. "Hey you know, when I have been getting the rentals from you all of the AL tanks have been to 3500 PSI. I did not think this was a safe thing to do." If he says that it really is not a big deal I would then tell him that it makes you a little unconfortable and would rather have the tank with only 3k in it, and that when you are having you personal tanks filled you do not want them over 3k. Overfilling an AL will shorten the life quite a bit from what I am told. At 3500 I would not be worried about the tank exploding or anything because they are hydro'd at much higher pressures but all that overfilling will basically wear out the metal and there will not be enough stretch and rebound to pass another hydro. I appreciate a full fill but I also would like my tanks to be around for a few more than just 5 years.

Please keep us up on what happens with the LDS after you say something. If you decide to say something.

Phil

Jipps
10-24-2007, 22:41
Definately let them know about it when it comes to your personal tanks, but if your worried about the pressure on a rental, check it when u get it. If its too high, either bleed some off or just ask for a different tank. Most dive shops wont mind if u want a different rental as long as you havent left the shop yet. I recomend using your gear to check the pressure, my store just spend a few $100 on new guages for the front and back, because our old ones were reading 200-300 over what the pressure really was. Rarely will you have this problem with your personal gear, especially if you have an air integrated computer.

finflippers
10-24-2007, 23:53
Every time we get aluminum tanks from our LDS they are filled to 3500 psi. I know they are rated at 3000, and haven't said anything since they are comping us the tanks until ours get back from hydro, but it's always made me wonder. Is this common practice?

Is the tanks freshly filled when you get them? They will over fill the tanks some not usually 3500 but about 3200 to 3250 and when it cools it should be just over 3000.

Aussie
10-25-2007, 02:15
I can only comment on tank fills over here (Australia). Australia regulation recommends that scuba cylinders should not be filled over 3000psi or 207bar. Most cylinders would be over filled and allowed to cool down to that amount especially in warm areas.
Luxfer Aluminium cylinders here in Australia have a working pressure of 240bar /3500psi. Luxfer also have a 15 year garrantee on their cylinders also. I think the test pressure of the luxfer here 360bar/5200psi. We also have our cylinders hydro tested every year.

Personally I would prefer my luxfer Al to be filled to 3500psi everytime. If it failed an annual hydro I get a new one.

Aussie

mm2002
10-25-2007, 11:18
The tanks are freshly filled when we get them, but we don't check the pressure until we're at the dive site. I guess when they're hot they must be filling them to what, 3700??
Anyway, I'm glad to hear it's no danger, but I am going to bring it up next time we're at the LDS.
I really appreciate all of your input.

RonFrank
10-25-2007, 11:29
AL80's are hydro'd at 5000psi. The tanks can handle 3500 psi, but yeah, hot, those tanks are likely at 3700~3800 psi. I am assuming that your SPG is accurate, which is something you may want to ensure.

An AL80 filled to 3500psi is not dangerous, or going to explode. I'm betting a lot of divers wished they had this issue. Heck, some LDS's won't fill HP steel tanks to 3500 psi which is what they are made to handle! :smiley5:

DarkCoffee
10-25-2007, 11:38
I have to agree that a 3500 # fill should not be an issue for the AL tank. As a colder water diver, a 3400# fill (room temp) can drop to 3000# or less in cold water.

I would think the more common risk is that the burst disk pressure might be approached if the tank was stored in sunlight and started to heat up.

(A burst disk going in an enclosed space like a van or SUV is something to be experienced to really appreciate:yikes: :yikes:)

Iceman
10-25-2007, 11:44
Man, I wish I had your situation! Instead it is more common for tanks to be filled to 3000 hot then down some number when they cool and another lower number when they hit the water.

Sometimes the OP has a faulty gauge. Last time their gauge said 3K but it was really 2.7K.

By the way, are you sure your gauge is accurate? His gauge?

mitsuguy
10-25-2007, 13:07
I have to agree that a 3500 # fill should not be an issue for the AL tank. As a colder water diver, a 3400# fill (room temp) can drop to 3000# or less in cold water.

I would think the more common risk is that the burst disk pressure might be approached if the tank was stored in sunlight and started to heat up.

(A burst disk going in an enclosed space like a van or SUV is something to be experienced to really appreciate:yikes: :yikes:)

I can't find the calculations right now, but I think a 60 degree difference in ambient (100 degrees to 160 degrees) only equals about a 300-400 psi difference in internal tank pressure... even if you started at 3500, it might be 400-500 psi bump in pressure, and the discs are set to release at 4200 psi... could get pretty close depending....

CompuDude
10-25-2007, 13:48
One way to help (not guarantee) you get the correct pressure on your fills is to get a paint pen and write "3000 psi" on the neck of the tank. Very commonly done around here, with a variety of HP, LP and MP (?) tanks floating around, sometimes it's hard to tell at a glance what should go in.

I have no issue with an Al tank filled to, say, 3300 psi, but 3500 psi on a regular basis is pushing it, IMO. Not likely to actually put your life in danger (the vast majority of tank failures occur during filling, not during use or any other time), but it's definitely shortening the life of your tank. Aluminum is not as elastic as steel and doesn't recover from overfills as well. Hydros happening once every 5 years are completely different from regular overfills.

DarkCoffee
10-25-2007, 14:29
Something along the lines of (P1*V1)/T1 = (P2*v2)/T2 but I always screw up the units.

mm2002
10-25-2007, 19:02
Hydros happening once every 5 years are completely different from regular overfills.

I can definitely relate with that logic. I know from my own engine building experience that, unlike steel, aluminum fatigues with expansion and contraction, and under physical stress. Steel does not "fatigue", it stays pretty consistent in strength throughout it's life.

One decision I've made throughout all this is that when our tanks come back from hydro, I'm going to demand they not be filled over 3000 cold. They can do what they want with their rentals.

cummings66
10-29-2007, 19:32
Something I wanted to say to counter a post which basically seemed to be saying a 3400 psi fill couldn't drop down to 3000 psi. Yes it can if it's a hot fill. I have an HP steel tank and I will guarantee you that a hot fill to 3500 psi will usually result in a cold pressure of 3000 psi. In fact I topped my tank for this past weekends dive and the ending fill pressure was 3700 psi. Care to guess what the cold pressure was? 3100 psi. It was a hot fill that I couldn't convince the monkey to not do. He thought he knew how to fill tanks even though I told him it was too fast and I'd never have 3500 psi. I wish he was around when I came back so I could say I told you so.

Depending on the tank, a hot fill will drop more than you'd realize.

cummings66
10-29-2007, 19:37
I wanted to add, on an AL80 I wouldn't sweat a 3200 psi fill. I don't think I'd demand a 3000 psi fill as they will either give you a hot 3000 fill giving you maybe 2700 psi of air, or they'll ask you to leave the tanks and come back for them. They'll still overfill by a small amount and you'll get your 3000 but you'll make two trips.

When I used AL80's they'd fill them to 3200 psi and I'd have 3000 when I dove it.

mm2002
10-29-2007, 21:17
I don't know if this matters or not, but our LDS has a bunch of larger tanks all hooked up together that they fill the scuba tanks from. They don't fill each one directly from the compressor. Basically, the tank they're filling is just equalizing with the group of larger tanks. That's probably the reason none of our tanks have ever been "hot". I'm guessing that all of the larger tanks must be kept at 3500? I've seen them fill 10 tanks without the compressor ever kicking on.

cummings66
10-29-2007, 21:59
That's called a bank. The theory is you have a bunch of HP tanks filled and then you put valves on them all. You'll open a tank up and fill the scuba tank as much as you can, then you switch to another tank, and so on so forth until your scuba tank has the correct fill.

The tank used first gets lower in pressure up until the last one which will be the highest in pressure, they all start the same however.

The compressor isn't hooked up live, it's used to top those banks up so that they can fill tanks. Getting hot has nothing to do with the source of air, it's how fast they fill a tank. If your tank is stone cold after a fill they're well above average and probably take 30 minutes to fill one tank, very unusual. Also they're way over filling your tanks if you have 3500 psi at the end of a cold fill like that. By cold fill I mean you can touch your tank and it's cold to the touch, not warm or hot.

The actual bank pressure can be very high, exceeding 4500 psi in some cases. Depends on what they fill and their compressor. If you're filling 3500 psi tanks you can bet it's well over 3500 psi to do that or they'd only get a few tanks topped off.

Puffer Fish
10-30-2007, 00:33
I don't know if this matters or not, but our LDS has a bunch of larger tanks all hooked up together that they fill the scuba tanks from. They don't fill each one directly from the compressor. Basically, the tank they're filling is just equalizing with the group of larger tanks. That's probably the reason none of our tanks have ever been "hot". I'm guessing that all of the larger tanks must be kept at 3500? I've seen them fill 10 tanks without the compressor ever kicking on.
You might want to consider that your gauge may be off. I have 4 spg's and two air integrated computers.. the highest (and it happens to be the newest) is off by around 400 psi high... the lowest is 200 psi low. I know because I have a calibration gauge, but most people and most shops do not.

It could be your gauge is just reading high...or their's is reading low.. or some of both...

Before saying anything, take a look at the gauges they are using and see if they are high accuracy ones...if they are, then you are most likely off. If not, then anything is possible.

CompuDude
10-30-2007, 04:15
Something I wanted to say to counter a post which basically seemed to be saying a 3400 psi fill couldn't drop down to 3000 psi. Yes it can if it's a hot fill. I have an HP steel tank and I will guarantee you that a hot fill to 3500 psi will usually result in a cold pressure of 3000 psi. In fact I topped my tank for this past weekends dive and the ending fill pressure was 3700 psi. Care to guess what the cold pressure was? 3100 psi. It was a hot fill that I couldn't convince the monkey to not do. He thought he knew how to fill tanks even though I told him it was too fast and I'd never have 3500 psi. I wish he was around when I came back so I could say I told you so.

Depending on the tank, a hot fill will drop more than you'd realize.

A 700 psi drop from a hot fill? I'd look for another ISP... fills that hot are *really* bad for your tanks.

Generally, 200-300 is to be expected, but 700 psi is really extreme.

cummings66
10-30-2007, 07:07
I agree that that's extreme, but like I said it was this one fill monkey who doesn't know what he's doing. The other two fill it fine, but this one is a dandy. I've talked to the owner and said my piece, but I do know the larger the tank the more likely it is to have a big drop on a hot fill. Take an AL40 and give it a got fill and you'll have less drop than an HP120 like mine given the same fill rate. Percentages.

It's just one know it all fill monkey who can't get it right.

mm2002
10-30-2007, 08:56
That's called a bank. The theory is you have a bunch of HP tanks filled and then you put valves on them all. You'll open a tank up and fill the scuba tank as much as you can, then you switch to another tank, and so on so forth until your scuba tank has the correct fill.

The tank used first gets lower in pressure up until the last one which will be the highest in pressure, they all start the same however.

The compressor isn't hooked up live, it's used to top those banks up so that they can fill tanks. Getting hot has nothing to do with the source of air, it's how fast they fill a tank. If your tank is stone cold after a fill they're well above average and probably take 30 minutes to fill one tank, very unusual. Also they're way over filling your tanks if you have 3500 psi at the end of a cold fill like that. By cold fill I mean you can touch your tank and it's cold to the touch, not warm or hot.

The actual bank pressure can be very high, exceeding 4500 psi in some cases. Depends on what they fill and their compressor. If you're filling 3500 psi tanks you can bet it's well over 3500 psi to do that or they'd only get a few tanks topped off.

Good info, thanks Matthew.
The times we've had to wait for the tanks, it took around 10 to 15 min to fill them, and they weren't warm to the touch (that I remember). Most of the time they are already filled and they just run back and grab us a couple. That was the case last weekend, and when we got to the lake both tanks were at 3500. I wouldn't think gauge inaccuracy is the issue since both mine, and my wifes gauges read the same.

I did finally bring it up to one of the guys (in a nice "play dumb" sorta way), and he said that they just bought a new compressor and they don't have it dialed in yet. That makes no sense to me, but I don't know anything about those types of compressors.

BSea
10-30-2007, 09:27
I did finally bring it up to one of the guys (in a nice "play dumb" sorta way), and he said that they just bought a new compressor and they don't have it dialed in yet. That makes no sense to me, but I don't know anything about those types of compressors.
That doesn't really make much sense. The compressor for a banked system doesn't determine the tank pressure. It's the person filling the tank, and watching the pressure in the tank. Maybe their's has an automatic safety cutoff at 3500 (Not a bad idea actually). That way if the person filling the tanks gets distracted, they wouldn't fill past that point. Regardless, it sounds like he was just giving you an answer to get you to leave him alone.

I have been to a dive shop in the cave country in FL that filled everything to 3600. They had about 10 whips, and filled everything to 3600 unless you asked them to take your tank off early. I wouldn't let him fill my lp tanks that high. Now they got paid by the cubic foot, so I guess it's more profitable for them to fill everything that high. Plus it's pretty standard practise in cave country from my experience.

in_cavediver
10-30-2007, 11:37
I did finally bring it up to one of the guys (in a nice "play dumb" sorta way), and he said that they just bought a new compressor and they don't have it dialed in yet. That makes no sense to me, but I don't know anything about those types of compressors.
That doesn't really make much sense. The compressor for a banked system doesn't determine the tank pressure. It's the person filling the tank, and watching the pressure in the tank. Maybe their's has an automatic safety cutoff at 3500 (Not a bad idea actually). That way if the person filling the tanks gets distracted, they wouldn't fill past that point. Regardless, it sounds like he was just giving you an answer to get you to leave him alone.

I have been to a dive shop in the cave country in FL that filled everything to 3600. They had about 10 whips, and filled everything to 3600 unless you asked them to take your tank off early. I wouldn't let him fill my lp tanks that high. Now they got paid by the cubic foot, so I guess it's more profitable for them to fill everything that high. Plus it's pretty standard practise in cave country from my experience.

Many shops, especially busy ones have installed regulators that limit the pressure automatically. They are standard items on SCBA fill stations as well. That said, smaller low volume shops simply can't justify the cost for the number of tanks filled. As for bank pressures, many run in the 4500-6000psi range. The problem with lower pressure banks is the drop in pressure and full fills. That's why LP tanks are easier to get 'full' fills from small banks.

As for the fill practices, my opinion is AL tanks ought to get either a cold 3000 or 'warmish' 3300-3400 fill. 3500 is just a bit on the outside and I wouldn't worry about it once or twice but I would not want it every time.

Steel tanks, well there are a LOT of steel tanks in cave country that have been through 2-3 hydros (official) and have seen nothing but 'cave fills'. My own 104's who have seen a large number of good fills passed hydro no problem. That said, if buying tanks, the newer HP tanks are pretty much LP tanks with a cave fill. If cost isn't a major difference - why not just get those. Mind you, they are a relatively recent introduction. My 104's are 5.5 years old and 130's didn't exist when I bought them.

Now, change topic - anyone know a good source for LP85's/HP100's? I need 4 or so to go with our new nomad sidemount rigs.