kc
Regular Diver
Posts: 16
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Post by kc on Nov 3, 2005 18:54:33 GMT -8
Hi you guys, i'm determined to dive using this methodology in vintage diving (quarry i go to is only 23' deep or so) but there's one thing i'm paranoid about and was seeking help on: water entering your tank
for example if you're using an spg you generally know to go up at about 500 psi or more which is more than enough to keep water out, but what about when you're not using one? Just how much psi does it take to keep water out? I mean suppose you dive till your reg gets hard to breathe then ascend... is there any chance of water getting in this way?
Thanks so much for the replies.
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Post by duckbill on Nov 4, 2005 0:12:59 GMT -8
Hi KC. If you are going to forego the SPG, you'd better be using a reserve valve of some type. The J-valve is the most common, and works very well. It is always a good idea to use a SPG in conjunction with the J-valve the first few dives to verify that the reserve function is, indeed, working properly, and to determine for future reference at what pressure the mechanism activates. Once the J-valve indicates reserve pressure it is time to surface, not play for 10 more minutes. Knowing your air consumption becomes much more important when diving this way so that you can estimate how much time you have left in your air supply at any given time for any given depth and activity.
As far as I know, water should not enter the system as long as the pressure inside the tank(s) exceeds that of the ambient external pressure, i.e. 14.7 psig@ 33 fsw, 29.4 psig@ 66 fsw, etc. I may be wrong to say that and I'm sure that someone will let us know if I am. However, I would never push that threshhold anywhere near that far. Besides, once your intermediate pressure drops below about 90(?) psi or so (depending on the design of the regulator), you would begin to have difficulty drawing breaths. It should become obvious before the pressure drops low enough for water to enter.
Get this: When I first started diving J-valved doubles, I had to figure out how it was safe for the tanks (as far as water entering) to suck one tank dry before tripping the J-valve to equalize the remaining pressure from the J-valved side into both tanks. That's when I figured out that the one tank does not become even nearly completely empty due to the facts mentioned above regarding breathability and the IP. My twin 50s' J-valve activates at 700 psi and they equalize to 400 psi once tripped, which means that there was 100 psi remaining in the non-J-valved tank before I tripped the J-valve. Fun stuff!
Most J-valves activate at around 300-400 psi for singles, 500 for doubles, and 700 for triples. I, personally, like my doubles to trip at 700, so that they equalize to 400 psi once tripped.
Everyone has their own preference for what pressure signals end-of-dive, but keep in mind that not all tanks are created equal. 500 psi in a aluminum 80 equates to approximately 13 cu.ft. of remaining air- a pretty good amount to consider adequate for emergency reserve for recreational diving. Let's take that 13 cu. ft. of air and see what different tanks would have to be, pressure-wise, to retain that same 13 cu. ft. Steel 72 = 450 psi Twin 38s= 300 psi Twin 50s= 260 psi, nearly half that of the aluminum 80, but the same amount of air! Some dive shops raise their eyebrows at this when I bring them in for a fill, so I have to sometimes explain it to them and hope they can understand it. It all has to do with the capacity and working pressure of the tank(s) in question. You can do the math for any tank. Divide the working pressure of a tank by it's capacity to find psi/cu. ft. Then multiply that by 13 cu.ft. (or whatever one feels is an adequate amount of emergency reserve air) to find the pressure for 13 cu. ft. of air for that tank. Example: For a standard steel 72: 2475 psi/71.55 cu.ft. = 34.59 psi/cu.ft. 34.59 psi/cu.ft. X 13 cu. ft. = 449.67 psi@13cu.ft.
Food for thought.
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Post by nemrod on Nov 4, 2005 0:33:18 GMT -8
Is your tank a steel tank? If not it is not so big a deal. Take the valve off and dump it out--lol. I think you are worrying over a non issue, water cannot get into a tank with some air pressure still remaining. The way water often gets in is to empty the tank but even then the regulator is in place and water would have to back flow through it. The way water get's in most tanks is during filling. Either moisture in the air or when they drop the tank in the fill bath water enters the opening in the valve and then when connected to the fill valve and pressure is turned on it is pushed into the tank. I agree, find a J valve for your vintage diving and confirm that it works before depending upon it and of course periodicaly check to ensure it has not been activated. James
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Post by Captain on Nov 4, 2005 5:50:44 GMT -8
It is virtually impossible to get water in a tank while diving. As Nemrod said most water get in during filling.
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Post by SeaRat on Nov 4, 2005 9:14:46 GMT -8
It is virtually impossible to get water in a tank while diving. As Nemrod said most water get in during filling. Actually, it is not implossible to get water into a tank while diving. All you need to do is: 1. Use a single hose regulator, with a normally-open first stage (diaphragm). 2. Suck all the air out of it on the surface (this can happen when diving in high chop situations). 3. Descend (if you descend to about 33 feet, or two atmospheres pressure absolute, you will create quite a suction, but any descent will create the negative pressure if the tank is not pressurized). 4. Touch the purge button of the second stage. This opens the demand stage, and the vacuum will suck the water into the tank. Note that this is most easily accomplished with a single hose regulator. Double hose regulators have air surrounding the second stage, and (usually) non-return valves in the mouthpiece which would keep the second stage dry. Therefore, KC's concerns are from his training while using a single hose regulator, and not from vintage equipment (double hose regulators). All the information above is correct about use of a J-valve. Usually, the spring pressure setting is about 300 psi for a single tank, and that is above ambient pressure. So if you're at 33 feet, the J-valve's 300 psi spring will activate fully at 314.7 psi (theoretically). At 66 feet, that's 329.4 psi ambient, but guage pressure will be 300 psi. John
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Post by luis on Nov 4, 2005 10:43:13 GMT -8
I believe the only J valve that compensates for depth was the Scubapro DCAR valve. The DCAR stood for Depth Compensated Adjustable Reserve valve. I recall when they introduced it and they made a big deal about it.
The DCAR valve has a small orifice to allow ambient pressure to push on the reserve valve plunger. It also has a slotted piece on the top you can push down and turn to change the spring tension. That changes the reserve from 300 psi to 600 psi.
All other valves that I am aware of have a sealed reserve chamber in the valve with no means of sensing or compensating for changes in ambient pressure.
In my experience, I have found it difficult (not impossible) to drain tank below about 80 psi with a two stage regulator. It could happen if you have a leak or free flow. Another way you can drain a tank easily is with a BC power inflator at the surface (I know that doesn’t apply in this vintage diving situation).
I dive a lot in fairly shallow water (less than 30 ft) and it is not uncommon for me to suck my tank down to where my Royal gets hard to breathe (at the end of my dive when I am close to shore). At that point I am very careful that not much more air is released.
As long as air under pressure (any pressure) comes out of the tank nothing can go into the tank, unless it is at higher pressure. This could normally only happen with the filler hose. This is way it is imperative the valve and filler hose connection is dry before filling.
Like SeaRat explained taking a tank with very low pressure back down into deeper water is another way of getting water into it; with either the valve open (with no regulator) or through some regulators. If I can not get any more useful air out of the tank I make sure my valve is closed.
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kc
Regular Diver
Posts: 16
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Post by kc on Nov 4, 2005 11:39:25 GMT -8
Is your tank a steel tank? If not it is not so big a deal. Take the valve off and dump it out--lol. Nope i'm using an al 80 and a dw mistral, but if a person did that they'd have to get a vip, unless they knew how to vip (which i don't) and i don't plan on using a j-valve either, just for the record (various reasons, ebay, have to get it checked, possibly rebuild etc. ) if i specifically wanted to dive a j valve i'd be different. but they're just not practical for my purposes/circumstances atm. The way i understand it... just k valves were used from about 1950-1960 w/ no spg right? That's pretty much the type of method i was going to use. I heard somewhere that a reg will get hard to breathe around 200 - 100 psi or so is that correct? I'm really not concerned w/ an out of air situation, i've got a pony bottle for that if worse comes to worse. and a buddy for that... i was just worried about the water in the tank = explosion issue, anyway thanks again for the replies, they've been usefull/interesting and again i appreaciate it.
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Post by nemrod on Nov 4, 2005 12:18:35 GMT -8
"Nope i'm using an al 80 and a dw mistral, but if a person did that they'd have to get a vip, "
No, why would you have to get a VIP? You can remove the valve on an EMPTY tank and reinstall it yourself and it cannot affect a VIP and who would know anyway--it is your tank.
"The way i understand it... just k valves were used from about 1950-1960 w/ no spg right?"
No, in that period J valves were commonly used with no SPG.
"That's pretty much the type of method i was going to use. I heard somewhere that a reg will get hard to breathe around 200 - 100 psi or so is that correct?"
Well, maybe, maybe not.
"i was just worried about the water in the tank = explosion issue, anyway thanks again for the replies, they've been usefull/interesting and again i appreaciate it."
Explosion? never heard of a tank exploding because it got a few drops of water in it. Aluminum tanks do not explode and neither will a few drops of water cause it serious damage that it would explode.
"Hi you guys, i'm determined to dive using this methodology in vintage diving (quarry i go to is only 23' deep or so) but there's one thing i'm paranoid about and was seeking help on: water entering your tank"
If your determined to do something a certain way then why ask opinions?
Nemrod
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kc
Regular Diver
Posts: 16
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Post by kc on Nov 4, 2005 15:33:12 GMT -8
" If your determined to do something a certain way then why ask opinions? Nemrod Just because a person is determined to do something doesn't mean they'll do it - which is the purpose of this thread. As for tanks exploding from water on the inside i've heard of it on the internet. there was a dock worker whos tank exploded from rust on the inside due to water going back up in it, and there was another account.
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Creed
Pro Diver
Posts: 189
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Post by Creed on Nov 4, 2005 18:51:29 GMT -8
" If your determined to do something a certain way then why ask opinions? Nemrod Just because a person is determined to do something doesn't mean they'll do it - which is the purpose of this thread. As for tanks exploding from water on the inside i've heard of it on the internet. there was a dock worker whos tank exploded from rust on the inside due to water going back up in it, and there was another account. If you have your tank vip'd every year, any corrosion will be caught long before it is a danger. I would suggest either finding an old Dacor valve with a high pressure port on it(and attach an spg), or using a J valve. But either way, don't worry about water in the tank unless you totally drain that puppy. Even then, if you are uncomfortable, drop it by your lds for a quick inspect and fill.
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Post by luis on Nov 4, 2005 19:29:06 GMT -8
There have been several studies related to tank corrosion. In particular at Battelle Memorial Institute and the University of Rhode Island. To make a long story short, the presence of water, especially salt water, in combination with the high partial pressure of oxygen in a SCUBA tank can cause enough oxidation to cause a tank to fail in a relatively short time period. It is worst for steel tanks, but aluminum tanks will also pit.
In one test (in the 1970’s) at the University of Rhode Island they kept steel tanks with a little salt water and full pressure in a warm environment. At the end of a 100 day test the tanks had lost as much as 2/3 of the wall thickness. This is enough for a catastrophic failure / explosion.
If your tank is ever fully discharged (empty) you don’t need a new VIP sticker, but you do need to make sure the inside is dry before refilling. The easiest way to check is to look inside.
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kc
Regular Diver
Posts: 16
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Post by kc on Nov 4, 2005 20:09:30 GMT -8
That was some neat info Luis, thanks. btw Nemrod: www.divinghistory.com/timeline.htm1951 - The Reserve Valve (later designated "J" valve by U.S. Divers according to its placement in their 1953 catalog) was released. You were right, however i could have sworn i heard a guy say on a diving msgboard that they didn't "catch on" till the 60's /70's. It really couldn't possibly been the 70's though according to other info on the above link. But anyway he used a k valve only at that time, and the method i described, and so did people he knew. I can't really remember the details of the msgboard thread, though. Maybe j valves were on short supply where he lived at the time... *shrugs*
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Post by SeaRat on Nov 4, 2005 20:30:13 GMT -8
I believe the only J valve that compensates for depth was the Scubapro DCAR valve. The DCAR stood for Depth Compensated Adjustable Reserve valve. I recall when they introduced it and they made a big deal about it. The DCAR valve has a small orifice to allow ambient pressure to push on the reserve valve plunger. It also has a slotted piece on the top you can push down and turn to change the spring tension. That changes the reserve from 300 psi to 600 psi. All other valves that I am aware of have a sealed reserve chamber in the valve with no means of sensing or compensating for changes in ambient pressure... From the 1972 Scubapro catelog: The advantage of this valve wasn't that it was "depth compensated," but that you could change it from a 300-psi reserve to a 600-psi reserve. The fact is that all J-valves and automatic (calibrated oriface) reserve valves are depth compensated, in that they function through the regulator. Here's what Fred Roberts in Basic Scuba says: There has been a great deal of misunderstanding of this concept, and in fact some instructors and authors have gotten it wrong: Please note that Mr. Balder in the above writing is wrong. If that were true, then at somewhere around 670 feet of sea water there would be no reserve at all. Mr. Roberts has this one pegged correctly, as when we use a diving regulator, the system senses the ambient pressure. Concerning the Scubapro D.C.A.R. valve, I have one, and I appreciate this being brought up as I did not know I could change it from 300 psi to 600 psi, and I'm going to set mine at 600 psi. But the depth compensating part of it is simply a marketing tool as all these J-valves had that built-in quality, and there is not much difference in the spring mechanisms between the manufacturers. Bill Barada, in Let's Go Diving (1962), calls the J-valve a "constant reserve" valve giving 300 psi of reserve. In their 1970 catelog, US Divers Company says that the "J" Valve is "The U.S. Divers invention that gives you a foolproof, time-tested and reliable 300 psi pressure-compensated air reserve warning." John
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Post by nemrod on Nov 4, 2005 22:51:17 GMT -8
KC, in the 50s and 60s there were several regulators with built in reserve mechanisms or sonic alarms etc. I bought in 1966 a Calypso J. The J was because it had a built in J type reserve so the regulator could use the increasingly common, as rental, K valve tanks and still have a conventional 300 psi reserve. You will hear lot's of stuff on the internet but this place is populated by people who were atually there and actually diving at that time----I barely qualify among these guys---many actually were involved in early dive instruction, wrote texts and papers and are in fact experts. When I arrived on the diving scene circa 1966 as a pre teen I definitly had a J valve tank when diving as did most every one unless they had a spg or a regulator with a reserve mechanism. I had, during that time, a Mistral and a Calypso J. I also had a Nemrod outfit which was also J valve. Sure, people dove then and now with a K valve and no spg or reserve----in shallow diving I am sure you can get away with it--I would not prefer to push my luck needlessly.
"As for tanks exploding from water on the inside i've heard of it on the internet. there was a dock worker whos tank exploded from rust on the inside due to water going back up in it, and there was another account. "
Again this is mostly urban legend. There have been some ruptured tanks but a lot of this is gross exaggeration. Also, by the way, you mentioned you had an aluminum 80. Aluminum does not "rust". Rust is by definition the reaction residue Noun) or process (verb) which by oxygen combines with ferrous material--IRON. Steel alloy such as what steel tanks are constructed from contain iron. Steel is an iron alloy. Aluminum contains no iron and can therefore not rust. It can corrode via other reactive processes but generally the damage occurs more slowly and with the 6061 aluminum alloy used in aluminum tanks can be self limiting to a degree. The short is that you do not need to worry so much about water in your tanks regardless of what you read on the "internet". If your having your tank inspected yearly unless something unusual is going on then I am sure your OK.
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kc
Regular Diver
Posts: 16
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Post by kc on Nov 5, 2005 0:55:00 GMT -8
Actually Nemrod these are actual news reports not urban legends. If you don't believe the dangers of tank explosion from rust/corrosion whatever you want to call it look on the internet and you'll find them. Didn't you see Luis's post? That's some more examples. Just because a person's asking vintage diving questions and has a low post count doesn't mean they're a drooling idiot lol.
Anyway in regard to the other things you said yeah i saw one of those single hose regs w/ the reserve like you're talking about on ebay. Makes me wonder if one of the out of business mfg.'s ever made a 2 hose reg w/ a reserve like that. You know i just happened to think... there's probably a working j valve for sale on this site. Think i'll go check...
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