Water in tank – low pressure or air fill?

[Teamcasa]

In another thread the subject of breathing your tank too low will allow water into the tank. I maintain that as long as there is greater pressure inside the tank than the surrounding pressure, water can not enter. All bets are off if you bring the tank to zero. I also contend that moisture is more likely to enter during a fill than at any other time. In addition, a leaking valve will not allow water in as long as the tank has pressure.

 

[Doc]

True. Just like I said in the other thread.

You missed the point. Try re-reading this: http://www.scubaboard.com/forums/3365991-post80.html

 

[1_T_Submariner]

One of my friend had a pony that free flowed until empty and it did have water in it. I commented that he made his pony into a Thermos. I'm not sure if he went deeper after it was empty? Not sure what effect this would have.

I Think even a few PSI above ambient would keep water out. A defective drier on a compressor would be a good bet. (not sure if Scuba compressors use driers)

 

[Teamcasa]

Here's the fact: Tank valves that are in resort-use, they all leak. It may be barely noticeable, you might need bat's ears or soapy water to notice- but they all leak. Tanks that are filled 3200 psi on Friday Night and racked as the dive staff goes home (for the resort changeover days) are often down to 2200 psi on Sunday morning for the first divers of the new week.

Do a little math. If you rack a tank at, say, 100 psi, the air will leak out within minutes allowing the ambient salty humid air to insidiously enter and affect the threads and further mutz-up the valve. Mutzing is a technical term.

It's easy to have an empty tank begin to assume ambient air, even if you know you racked it with 500 psi. They all leak.

I don’t want to get into a flame over this but I think it has more to do with the heat generated by filling and the resultant cooling down that accounts for the pressure change more than any valve leakage.

 

[Wookie]

A better bet is the failure to blow out the whips prior to attaching to a tank valve, filling in a tub full of water (some misguided souls still think it helps cool the tank), and not ensuring the face of the tank valve is dry prior to hooking up the fill whip. 1 drop of salt water on the face of the valve and blown into the tank with high pressure air atomizes the water, and leaves a very interesting residue on the inside of an aluminum cylinder when seen with a blacklight. The resudue left in a steel tank results in condemnetion of the tank in many cases.

No, I'm not going to fight with you about the joys of filling cylinders in a water bath. It's kind of like the LDS vs internet debate. Or like wrestling with a pig...

 

[marchand]

Quote: Originally Posted by RoatanMan
Here's the fact: Tank valves that are in resort-use, they all leak. It may be barely noticeable, you might need bat's ears or soapy water to notice- but they all leak. Tanks that are filled 3200 psi on Friday Night and racked as the dive staff goes home (for the resort changeover days) are often down to 2200 psi on Sunday morning for the first divers of the new week.

Do a little math. If you rack a tank at, say, 100 psi, the air will leak out within minutes allowing the ambient salty humid air to insidiously enter and affect the threads and further mutz-up the valve. Mutzing is a technical term.

It's easy to have an empty tank begin to assume ambient air, even if you know you racked it with 500 psi. They all leak.

_________________________________________________________________________________

Why won't you try to do a little math. The rate at which air will escape a leaking tank is not constant, it will follow a logarithmic curve which means that the rate at which air will escape will decrease as the pressure drops. Consequently, a tank that looses 1000psi over the course of the first 35hrs will take ~twice as long to drop an additional 1000psi.

Also, I believed there was a discussion on the deco stop about the need to analyze the contents of both tanks on a set of doubles. One guy decided to forever settle the question, so (if I recall correctly) he took his doubles and filled one tank with 40% O2 and the other with air. After I think a week he then analyzed the contents of both tanks and found that they had not equalized (I don't remember the exact values, but I do not believe they were very close at all). What this means is that if a tank leaks till it is completely empty it will assume ambient air, but it will take a very long time before it can cause any damage.

 

[MauiScubaSteve]

I don't have to. Re-read the posts with greater care.

I say "when they're empty", Pete from Belize talks of the issue with extreme low pressure. Low pressure results in "empty". Here's why....

Here's the fact: Tank valves that are in resort-use, they all leak. It may be barely noticeable, you might need bat's ears or soapy water to notice- but they all leak. Tanks that are filled 3200 psi on Friday Night and racked as the dive staff goes home (for the resort changeover days) are often down to 2200 psi on Sunday morning for the first divers of the new week.

Do a little math. If you rack a tank at, say, 100 psi, the air will leak out within minutes allowing the ambient salty humid air to insidiously enter and affect the threads and further mutz-up the valve. Mutzing is a technical term.

It's easy to have an empty tank begin to assume ambient air, even if you know you racked it with 500 psi. They all leak.

This factor also gives rise to another Diver Myth. That 2200 psi tank that I mentioned... the one that new divers often find all racked up for the first dive of the new dive week? You will see this comment often in trip reports and resort/op comment cards: "The tanks were low on the first day so we complained and they kept them filled after that". No, you just pulled tanks that were very recently rotated and filled. They hadn't been sitting, leaking slowly for a weekend.

I've seen my share of dive op and resort operations in tropical environments. If I had a nickel for every tank valve I pulled and worked on, I'd have gotten a real job on an island. In a large-op, quite often at least one guy pulls and changes out valves, one day a week. All day, for 8 hours.

I have worked full time tropical resorts/charters/dive shops for the last 6 years, and while there are shards of truth in your rant, there is also considerable exaggeration. Those may be your facts, but I don't see anybody else saying they are also their facts!

As long as the person doing the vis knows what they are doing and does it every tank (new neck o-ring, cleaned mating surfaces, proper amount of grease properly applied), only a very small percentage of tanks will leak at the neck. Even the half-***** bargain basement vis (re-used neck o-ring, hastily scraped mating surfaces, sloppy greasing) rarely results in 15% neck leaks.

Valve handle leaks are possibly more common, but with the pampered and fussy resort/tourist cliental I've encountered, those tanks are not used long before getting set aside for repair. Additionally, those handles often leak very, very little when closed or opened all the way.

I am the first to admit that most valve o-rings leak a little during the dive, and in my opinion many locations in Hawaii got a bad batch last year, but that o-ring causes no leaks when the valve is shut. I personally doubt that small champaign bubbles are more than a couple breaths over the course of a dive.

I have worked at; a local dive shop with a boat, a 7 resort operation with fill service from a local dive shop, a 2 resort operation with a boat and a high volume resort operation (last 2 with on site compressors). Less than 5% of the tanks drop to 2200 psi in 3 days (and we dive just as much or more on the weekend).

Another thing I have noticed is those tanks will often still be at 2000 psi a week later when someone finally looks into the situation. In other words, when the pressure drops to a certain level it no longer leaks, so the idea of a 100 psi tank which leak a little at 3200 psi loosing the final 100 psi within minutes is ludicrous. If it had that kind of leak it would sound like a tea kettle when full!

Maybe I've been lucky to have better than average vis-ing / valve maintenance, but I did the vis-ing / valve maintenance at the first shop and there were very few neck or valve leaks, so I thought the 10-30% I've seen the last few years was on the sad side.

Perhaps I'm wrong, and I'd love to hear how blessed I am, so let's hear from other tropical resort dive professionals. Maybe Blesi from B&B dive shop (Maui) will tell us how many tanks they find water in and why she thinks it's there. Hopefully others will chime in, SB's been pretty boring this year (until this week).

 

[DeepSeaExplorer]

I guess it depends on where you're at. When I went to Bonaire, almost every tank leaked, so badly in fact you could hear and see the necks bubbling. But, that's just poor maintenance.

On one occasion, we had a lot of diving planned for the next day and loaded up the truck the night before. When we got to the dive site the next day many/most of the tanks were down several hundred PSI, one as low as 2200 IIRC. After that, we just got them the morning of the dive.

As I stated in the other thread, I'm a firm beliver that breathing the tank down is not the source of water in the tanks. I know from experience under controlled conditions. Besides that it just doesn't make sense. If you're breathing the reg and still getting air, how is water going to get in the tank?

Now, if you leave that tank with 100 PSI sitting with a bad neck o-ring and the 100 PSI leaks out, that's a different story. The tank is then open to changing humidity and barometric pressure.

 

[rmannix]

I had an AL80 that had a small amount of water found in it during a visual, the shop asked me where else I had been getting fills but the entire year it only was filled there.
Rarely did I surface without 900 PSI and never below 600. Noticed it was losing air between fills, and figured it was time for a valve rebuild. Following visual showed a crack in the neck. It was a 1982 Luxfer, failed the visual in 1992, before Luxfer acknowlwdged the 6351 alloy problem. I was teaching the whole time and it saw heavy use. Tank is now a nice lamp.

 

[Doc]

I don’t want to get into a flame over this

That should be a SB "given". We're here to share life experiences, not ego.

but I think it has more to do with the heat generated by filling and the resultant cooling down that accounts for the pressure change more than any valve leakage.

True, but remember- that moisture (from the filling) is devoid of salt. Ambient air is not. Also, remember what we are talking about here (the deal where dove ops and resorts demand a 500 psi return) is not defensible scientific reality- it is the "tropical myth" that grew from the occasional empties and the higher prevelance of corrosion due to volume of use, lack of attention, and guests gorilla cranking the valves.

This "truth" grew from a myth. We now assign other reasons to not breathe the tank down, but honest to God... I was "standing there" when this one got thought up. I stood in Caribbean dive ops in the 70's and silently and wide eyed, I absorbed what these dive gods were saying. It musta been so!

I have worked full time tropical resorts/charters/dive shops for the last 6 years, and while there are shards of truth in your rant, there is also considerable exaggeration. Those may be your facts, but I don't see anybody else saying they are also their facts!

I looked at your profile. Mine isn't exactly a full resume, but I gotta tell you that working in Florida and Hawaii in the 1990's isn't what I was referencing my own basis of experiences upon. My still using gear that is older than you isn't a badge of honor, but it does mean that I have used a rock as a hammer occasionaly. Travel the world- and that's what we are talking about here- in the long-ago era that this 500 psi thing arose, that was in the 70's in Cayman (and Nassau, Freeport, etc) At that time, in that era- you were really doing some adventurous diving- that was the edge of the world! Places that had no easy resupply of parts and trained repairmen- certainly no backup supply of tanks that were pulled out of rotation for service. Your experiences in Hawaii and Florida are a great thing- with that you can go anywhere and work- but remember~ we are talking about the birth on an ancient myth that grew legs and standing in the industry... long before you though about diving. Again- not a put-down, just a fact of chronology. It's history, dinosaur stuff.

Valve handle leaks are possibly more common, but with the pampered and fussy resort/tourist cliental I've encountered,

Again, my point exactly. Young Instructors that come to work in far flung Caribbean Islands are quite vocal in their praise of the guests... as compared to the Florida shop they worked in after their IDC at Pro Dive.

I am the first to admit that most valve o-rings leak a little during the dive...I personally doubt that small champaign bubbles are more than a couple breaths over the course of a dive.

There's another point- and this one I'm certain you'll agree- how many guests have registered their panicked distress over a leaking tank... one that was just zizzzzzing out 5psi/hr ? You've seen the panicked pointing and gesturing. Much the same as the alarm generated by a Sherwood Oasis. You have seen one of those antiques, right? They're still in use everywhere. First time somebody sees one, just like an inconsequential tank leak... woo-woo... call 911!

and in my opinion many locations in Hawaii got a bad batch last year, but that o-ring causes no leaks when the valve is shut.

And if you complained, your supply source could have you another batch overnighted to you, delivered to that Hawaiian dive shop by a uniformed guy in a little brown truck. Try that in the bulk of the rest of the dive world. UPS pretty well stops right where diving is still somewhat of an adventure.

I have worked at; a local dive shop with a boat, a 7 resort operation with fill service from a local dive shop, a 2 resort operation with a boat and a high volume resort operation (last 2 with on site compressors). Less than 5% of the tanks drop to 2200 psi in 3 days (and we dive just as much or more on the weekend).

so the idea of a 100 psi tank which leak a little at 3200 psi loosing the final 100 psi within minutes is ludicrous. If it had that kind of leak it would sound like a tea kettle when full!

Ahh, no. And it's irrelevant how it sounds. Remember a working operation has tank racks that are near the compressor noise. Put yourself in that third world environment. If that hissing sound isn't heard by the boss, nothing gets fixed. You are right- it is all about ongoing maint- something that simply doesn't exist in the "no problem, mon" world.

Perhaps I'm wrong, and I'd love to hear how blessed I am, so let's hear from other tropical resort dive professionals.

You heard from Peter in the other thread- an old goat that works in Belize. once again- remember- we aren't talking about reality- we're talking about the ancient urban myth that propagated this "500 psi" minimum rule. Talk to an old timer who worked in an op that didn't have a MallWart just down the street. This is how that myth began.

SB's been pretty boring this year (until this week).

This is a lot of fun, isn't it?

I guess it depends on where you're at. When I went to Bonaire, almost every tank leaked, so badly in fact you could hear and see the necks bubbling. But, that's just poor maintenance.

Bingo. In Bonaire, they have a pretty good pipeline of resupply. It still isn't Maui, but it aint Tobago, either. Here you hit upon another factor: extreme cheapness. Most dive-ops wont spend a nickel to save a buck. Many far flung ops are managed for local money men. Are they on site and are they aware of maint issues? Obviously not.

...We had a lot of diving planned for the next day and loaded up the truck the night before. When we got to the dive site the next day many/most of the tanks were down several hundred PSI, one as low as 2200 IIRC. After that, we just got them the morning of the dive.

That's same exact scenario I stated in the other thread. Now- take that one step further. If you "re-rack" a used tank that you have sucked down real low, the chances of that last couple hundred pounds leaking out un-noticed by the staff- pretty good. That's when the ambient, warm slat air comes in.

As I stated in the other thread, I'm a firm beliver that breathing the tank down is not the source of water in the tanks. I know from experience under controlled conditions. Besides that it just doesn't make sense. If you're breathing the reg and still getting air, how is water going to get in the tank?

True absolutely true. But remember- we are not talking about scientific reality... the point of the discussion is how this strange rule got started in the first place. Again I say- SCUBA folklore that gained credence by dive ops with corroded tanks. They "knew" why this was happening- because you damned tourists were emptying their tanks to zero.

Perception = Reality... begets legend and myth... and then rules carved in stone.

Now, if you leave that tank with 100 PSI sitting with a bad neck o-ring and the 100 PSI leaks out, that's a different story. The tank is then open to changing humidity and barometric pressure.

I think that is what I have been saying all along.