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Scuba Forum / General / March 2008How fast do you lose a tank of air after blowing gauges off
From a previous thread of mine re OOA situations I recounted my instructor losing his gauges at depth which we treated as an OOA situation. Many people pointed out that while this is a high pressure situation it is low flow so not really out of air. However I am sure I remember the hose stopping flowing well before we hit the 3m SS but it was 30 odd years and numerous bottles of home brew ago . Anybody got the actual figures on how quickly a 88 aluminium would drain after losing the gauges, is it dependent on depth and/or how the gauges came off "dechucka" <dechucka@vomithotmail.com> pounded away at his keyboard resulting in: :From a previous thread of mine re OOA situations I recounted my instructor :losing his gauges at depth which we treated as an OOA situation. Many people [quoted text clipped - 4 lines] :88 aluminium would drain after losing the gauges, is it dependent on depth :and/or how the gauges came off I don't think it's dependant on depth. I think it's a function of how much air is there to start with and how wide open the valve is. Dan Bracuk Never use a big word when a diminutive one will do. ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- > I don't think it's dependant on depth. I think it's a function of how > much air is there to start with and how wide open the valve is. Then try it at 6735 ft and see how quickly it stops bubbling...  SignatureSee NNTP header field "X-Real-Email-Address" to reply by email. Grumman-581 <grumman581-usenet-2008@spambob.net> pounded away at his keyboard resulting in: :Then try it at 6735 ft and see how quickly it stops bubbling... If that's above sea level, maybe. If it's below, I'll take your word for it. Maybe. Dan Bracuk Never use a big word when a diminutive one will do. ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- > If that's above sea level, maybe. If it's below, I'll take your word for > it. > > Maybe. Nope, not above sea level, I'm talking about depth... Run the numbers and calculate the pressure at that depth and you'll see what I'm talking about... SignatureSee NNTP header field "X-Real-Email-Address" to reply by email. > > If that's above sea level, maybe. If it's below, I'll take your word for > > it. [quoted text clipped - 3 lines] > Nope, not above sea level, I'm talking about depth... Run the numbers and > calculate the pressure at that depth and you'll see what I'm talking about... According to my calculations, you should get a very slow seepage... of water into the tank. > According to my calculations, you should get a very slow seepage... of > water into the tank. Yeah, I rounded off the depth... If I hadn't, someone would have complained about me having too many significant digits... <grin> SignatureSee NNTP header field "X-Real-Email-Address" to reply by email. > > According to my calculations, you should get a very slow seepage... of > > water into the tank. > > Yeah, I rounded off the depth... If I hadn't, someone would have > complained about me having too many significant digits... <grin> On second thought, I was wondering if it would matter if the tank were "upright" or inverted... If the tank were upright, would the air want to rise even though the water was pushing in (perhaps once equilibrium was reached)? >>> According to my calculations, you should get a very slow seepage... of >>> water into the tank. [quoted text clipped - 6 lines] > If the tank were upright, would the air want to rise even though the water > was pushing in (perhaps once equilibrium was reached)? If upright ALL the air would immedately escape upwards. (or water would flow in and push the air up, depending how you look at it!) > > "Grumman-581" <grumman581-usenet-2008@spambob.net> wrote in message news:pan.2008.03.10.22.45.20.672000@grumman581-usenet-2008-spambob-net... > >>> According to my calculations, you should get a very slow seepage... of > >>> water into the tank. [quoted text clipped - 9 lines] > If upright ALL the air would immedately escape upwards. > (or water would flow in and push the air up, depending how you look at it!) Immediately? It doesn't happen "immediately" at the surface. Is this true even if the external pressure was greater than the internal pressure? Does it depend on the size of the orifice? > Immediately? It doesn't happen "immediately" at the surface. > > Is this true even if the external pressure was greater than the internal > pressure? > > Does it depend on the size of the orifice? If the pressures are equalized and the orifice is facing upwards, there is a chance that water will go into the tank, but it's going to be fairly slowly considering how small the orifice is on our valves... It's probably going to be a function of the capilary action and surface tension of the water combined with the orifice diameter... SignatureSee NNTP header field "X-Real-Email-Address" to reply by email. [Default] Thus spake Grumman-581 <grumman581-usenet-2008@spambob.net>: >> Immediately? It doesn't happen "immediately" at the surface. >> [quoted text clipped - 8 lines] >going to be a function of the capilary action and surface tension of the >water combined with the orifice diameter... In this kind of situation, what you would have would be burping. Some water would get in until finally enough air was burped out to accomodate more air. Try it with a bottle of shampoo. > From a previous thread of mine re OOA situations I recounted my instructor > losing his gauges at depth which we treated as an OOA situation. Many people [quoted text clipped - 4 lines] > 88 aluminium would drain after losing the gauges, is it dependent on depth > and/or how the gauges came off If ya read the thread, the numbers are there from, as I remember, Al Wells and Scott. On the high pressure side, there is no need for volume so both the first stage and hp hose have pinhole passages. Regardless of where the failure is, the air escapes at high pressure but low flow. Did Al say 22 minutes to empty a full tank? It would be about the same whether the Bourdon tube burst or the hose burst. On the low pressure side, the regulator is built to flow a large volume, and the tank will drain considerably faster than it will in the case of a hp failure. A second stage free flow may occur with the demand valve wide open or less than wide open. With the valve wide open, the tank would drain about as fast as a ruptured lp hose or loss of the hose from the first stage. 8 - 10 minutes to drain a full tank is my guess, but someone will correct me. O-ring failure (extrusion of a large chunk of the o-ring) will drain the tank about as quickly as a lp failure because the gap between the 1st stage and the tank valve is still pretty small. Scott gave burst disk numbers which are a pretty fast drain rate, because that's what the burst disk is designed to do - dump pressure fast. None of these are depth dependent until the tank gets down to the ambient pressure, i.e. about 60# at about 100', then flow will stop. esg >> From a previous thread of mine re OOA situations I recounted my >> instructor losing his gauges at depth which we treated as an OOA [quoted text clipped - 34 lines] > > esg I am going to agree with Mike on this one. Here is Al's link. http://tinyurl.com/3e2wr9 If your SPG fails (as in lets gas escape), then worst case scenario is the same as a HP hose failure. About 22 minutes at any depth with a full Al80. >>> From a previous thread of mine re OOA situations I recounted my >>> instructor losing his gauges at depth which we treated as an OOA [quoted text clipped - 40 lines] > same as a HP hose failure. About 22 minutes at any depth with a full > Al80. Thanks for the link must of missed that post. I will have to go back to my log book to see exactly what happened. Probably find we were only at 6m it was a free flow and he didn't use my air and I have embellished the story over the years [Default] Thus spake "dechucka" <dechucka@vomithotmail.com>: >Thanks for the link must of missed that post. I will have to go back to my >log book to see exactly what happened. Probably find we were only at 6m it >was a free flow and he didn't use my air and I have embellished the story >over the years ie. we've been drinking too much. Which can never happen. >I am going to agree with Mike on this one. Here is Al's link. >http://tinyurl.com/3e2wr9 > >If your SPG fails (as in lets gas escape), then worst case scenario is >the same as a HP hose failure. About 22 minutes at any depth with a >full Al80. 22 minutes? HP hose failure? I don't think so, Tim. That looks like a typo to me. How about 2 minutes? Why does he choose to use minutes there instead of seconds as in all the other scenarios? How can a free flowing HPR drain a system faster than a "failed" HP hose? Are we talking full end cut off or just a minor cut? This would be more informative if all the units were seconds and all the values specified instead of "same within..." otherwise these estimates are totally useless. I suppose the uselessness of these data support the conclusion that any equipment failure should lead to an OOA abort. Quote: I completed the test on the surface (0 feet) with 4 aluminum 80s and a Zeagle D50 regulator. Here are the results 1. Failed Burst Disk = 72 seconds 2. Failed HP Hose = 22 minutes 3. Failed LP Hose = 83 seconds 4. Free Flow High Performance Regulator = 255 seconds I then repeated the test at 4 atms / 99ft 1. Failed Burst Disk = Same within a second or 2 2. Failed HP Hose = Same within a minute 3. Failed LP Hose = Same within a second or 2 4. Free Flow High Performance Regulator = 155 seconds I then repeated the test at 8 atms / 231ft 1. Failed Burst Disk = Same within a second or 2 2. Failed HP Hose = did not complete due to time restraints but would assume it would be with a minute difference 3. Failed LP Hose = Same within a second or 2 4. Free Flow High Performance Regulator = 91 seconds > 22 minutes? HP hose failure? I don't think so, Tim. That looks like a > typo to me. How about 2 minutes? I dunno about the actual numbers, but I'm quite certain that an HP hose failure (as in full cut, or just leaving the hose off the 1st stage) will take closer to 22 minutes than 2 minutes to empty an AL80. The 1st stage has a restriction in the HP port (look inside the port) to limit the flow through the port. SignatureArt Greenberg artg at eclipse dot net > How can a free flowing HPR drain a system faster than a "failed" HP hose? > Are we talking full end cut off or just a minor cut? This would be more > informative if all the units were seconds and all the values specified > instead of "same within..." otherwise these estimates are totally useless. > I suppose the uselessness of these data support the conclusion that any > equipment failure should lead to an OOA abort. The HP hoses tend to have rather small orifices in the fittings on the ends, unlike the LP hoses... I believe that many of the regulators also have small diameter orifices for the same reason... Assuming that it takes 22 minutes to empty an AL80 through a burst HP hose, one could probably get away with making a cheap set of doubles by hooking a short HP hose between two 1st stages... You would still want a 2nd stage on each 1st stage, but for shallower depths, you could probably get away with not having to switch 2nd stages periodically... One of these days, I'm going to have to give that a try... SignatureSee NNTP header field "X-Real-Email-Address" to reply by email. >>I am going to agree with Mike on this one. Here is Al's link. >>http://tinyurl.com/3e2wr9 [quoted text clipped - 9 lines] > How can a free flowing HPR drain a system faster than a "failed" HP > hose? Because of a better impedance match. Bernouilli rules. A broken HP line is basically a constant mass flow orifice, whichs flow is governed _only_ by supply pressure and orifice diameter, and not by ambient pressure. Unless you crack the reg side threads. Some reg do net have a throttle orifice inside the reg, some do. A free flowing perfomance reg, like a Jetstream, will blow out all the valve will deliver, that is something above 1100 l/min. > I completed the test on the surface (0 feet) with 4 aluminum 80’s and > a Zeagle D50 regulator. [quoted text clipped - 20 lines] > 3. Failed LP Hose = Same within a second or 2 > 4. Free Flow High Performance Regulator = 91 seconds This is consistent. Matthias > Because of a better impedance match. > Bernouilli rules. A broken HP line is basically a constant mass flow > orifice, whichs flow is governed _only_ by supply pressure and orifice > diameter, and not by ambient pressure. But the supply pressure is meaured in psig, not psia, so ambient pressure would have to have an effect upon it... SignatureSee NNTP header field "X-Real-Email-Address" to reply by email. >>I am going to agree with Mike on this one. Here is Al's link. >>http://tinyurl.com/3e2wr9 [quoted text clipped - 13 lines] > totally useless. I suppose the uselessness of these data support the > conclusion that any equipment failure should lead to an OOA abort. I doubt it is a typo. While the hose and the gauge are under high pressure, it is very low flow. Others have pointed this out. Your LP hose is designed for much higher volume and will therefore empty the tank faster. Your SPG which attaches to the HP port needs very little volume to read the tank. Maybe the author used minutes because he didn't want to write "1320 seconds". Or maybe to emphasize the difference in how fast the gas is depleted from the tank. > >I am going to agree with Mike on this one. Here is Al's link. > >http://tinyurl.com/3e2wr9 [quoted text clipped - 5 lines] > 22 minutes? HP hose failure? I don't think so, Tim. That looks like a > typo to me. How about 2 minutes? It is not a typo. Al's report of 22 minutes is consistent with a test done in 1999 by Undercurrent. In their test, it took 20 minutes to lose 55 cubic feet (AL80; 2500psi - 400psi). That article (February 1999) is still online, here: http://www.undercurrent.org/UCnow/articles/SpareAir9902.shtml > Why does he choose to use minutes there > instead of seconds as in all the other scenarios? In the case of the Undercurrent test, they simply got impatient after 20 minutes, so they stopped the test. Since the tank still wasn't yet empty (nor had it started completely full), they reported how much was still left. > How can a free flowing HPR drain a system faster than a "failed" HP > hose? Because they have different sized holes (orifices) for which any flow to occur through. An HP failure will drain a tank faster than an LP failure if the diameter of the holes are nominally the same. However, since 1982, they've not been. Contemporary regulator designs have purposefully restricted the HP port's orifice diameter so that it is close to the design ideal, which is communication of pressure information without any flow in the event of a hose failure. LP stages are specifically designed to supply volumes of gas. HP stages merely only need to communicate pressure to a gage. > Are we talking full end cut off or just a minor cut? In some of the tests (Undercurrent's), the HP hose was completely removed: a bare port in the regulator body. This is even more severe than cutting the full end off. > This would be more informative if all the units were > seconds... It might be, but don't look a gift horse in the mouth. When you've personally paid for the data collection, then you can complain about how it was reported. > and all the values specified instead of > "same within..." otherwise these estimates are > totally useless. None of these are estimates; they were DIRECT EVIDENCE TESTING. The variations in test measurement precision that you're complaining about are on the magnitude of only 5-10%, but you're neglecting the fact that the first trial that was done on dry land (where its easy) and the next two were done underwater (where its not as easy). > I suppose the uselessness of these data support the > conclusion that any equipment failure should lead to an OOA abort. I supposed that instead of complaining, you intend to go out and do your own dives to 100fsw and 230fsw to collect "more accurate" data to satisfy your need for greater precision. While you're at it, I suggest that you use 10 different brands of regulators, because variations in their internal designs will be a source of variation that is comparable to the variation you're complaining about here. If you don't do this, then some armchair a.shole can criticize your data collection as "useless" too. In any event, the question is not if an equipment failure should or should not lead to a dive abort. The question is in the knowledge of its severity so as to know if you have a small or large amount of time with which to handle the failure. For example, if its an HP hose, there's essentially no need for you to skip a safety stop. -hh > [Al wrote] > Quote: [quoted text clipped - 22 lines] > 3. Failed LP Hose = Same within a second or 2 > 4. Free Flow High Performance Regulator = 91 seconds > From a previous thread of mine re OOA situations I recounted my > instructor losing his gauges at depth which we treated as an OOA [quoted text clipped - 4 lines] > actual figures on how quickly a 88 aluminium would drain after losing > the gauges, is it dependent on depth and/or how the gauges came off For the depths that we dive, it is quite unlikely that we would notice any difference in the time that it took to empty a tank with a blown HP hose or gauge... Although it might take a bit of time for a full tank to empty, you need to look at it in the worst case of when you are already down to 500 psi or so and getting ready to ascend... If you assume 22 minutes for a full 3000 psi AL80 and a linear flow rate (bad assumption, I suspect), you are losing 136 psi per minute which gives you less than 4 minutes before you are truly out of air... If you start up immediately, you'll probably be OK, but if you try to spend some time trying to fix the problem (and you fail), you might be out of air by the time you make it to the surface... SignatureSee NNTP header field "X-Real-Email-Address" to reply by email. |
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