BSAC avoids annual VIP

[tbone1004]

I managed a shop in Tobermory in the very early '80s and I seem to recall that VIPs were just becoming a thing at that time. I have no recollection of there being a series of exploding tanks leading up to this, any more than there have been since. I also recall that the "qualifications" for we inspectors were suspect at best. Thankfully, at least that aspect has been improved.

VIP started as a means to protect the tanks from being condemned from pitting vs. anything exploding.

 

[rjack321]

If you think there is an actual error or omission, contact Mark and let him know. I can't say which way the conversation will go, but I bet one or the other of you will learn something new!

I just looked over my materials, and I would have had to call Mark for clarification. But based on what I found, I think the 3rd paragraph on page 28 of the 5th edition may address your concerns. He certainly does know about that thinner wall, as it is listed in the table on page 30.

I refuse to have any contact with PSI. My "certificate" from them has long since expired and I have no idea what is in their current training materials.

 

[NAM001]

I have a K14 with three filter towers. The first two are entirely 13X dessicant, the third is about half dessicant. I don't know their volume with the cartridges installed, so I don't know the total dwell time. The PMV on the downstream side of the towers is set at the pressure Bauer recommends. The club's compressor has similar filtration and about the same dew point. I could add refrigeration ahead of the coalescer if I were so inclined, I suppose. Increasing the PMV setting would dry the air more by increasing the dwell time but it's kinder to the compressor to leave it where it is set.

I still think that -200F difficult to achieve.

Also, since it's come up elsewhere in the thread, I will add my belief that the dew point is measured at STP (Standard Temperature and Pressure). It's considerably higher (a smaller negative number) under pressure, IIRC. That said, I never see evidence of condensation in my tanks (rust spotting) even when I dive in the winter, so around here, at least, -70 or so is "dry enough."

As stated in other posts I was in error on the -200 it should be -100 and you are also right on how dew point is measured. . while under pressure the RH is always 100% untill chemical drying is imposed.. It can not physically be less. as pressure goes up so does the ability of the air to release water. water removal (mechanical) uses this pressure to ring out the moisture. when it stops coming out you are at 99.999% RH. As psi goes up you ge more water removed. the dew point is a measurement in temperature that will cause the same condensation under standard 1 atm. with out your x13 you will never rerach -100. chemical drying takes over where mechanical stops. -70 is dry enough indeed. the higher the PMV setting the more mechanical drying occures. The more x-13 ,,,, the more chemical drying occurs. filtering after teh x-13 needs to be less than -50 to work properly. I read somewhere 100% rh is 2.5 - 3% by volumn water in the air. and if you pressure the 100% rh air to 10 atm you will remove 90% of the moisture. leaving when returned to 1ATM will mow be 10% rh. That is why after exposing my tanks insides to room air. I fill to perhaps 1000 psi and vent a couple of times. the blending of the 60% rh air in the tank and the compressor DRYER air pretty well removes any untreated atmosphere contaminants from the tank. I have not read the x-13 stuff for a while so i dont know if to get it you have to have a PMV set to 3500 or what ever. No matter what teh output of hte X-13 will be a dwell issue. teh higher teh PMV the drier teh air enter ing teh x-13 bed. normally the Pmv is set to a presure that allows the compressor to run physically ballanced on all stages. I think my rix calls for 1900 psi. and perhaps the bauer at 2500 or so. Quite often i see recommendations of 2800 to max the mechanical condensing. 2800 may be highfor teh ballancing but teh pv only is in play till the tank psi exceeds it. I have seen many configurations using many PVM's one on the compressor output to minimize the start up banging of the last stage floating piston. another the final moisture separator output. and another after each moisture filter stack. even then the use varies if yo are using dedicated stacks or combo stacks. most of us use combo stacks. desicant carbon and perhaps monoxicon.

 

[Bob DBF]

I was trained to leave some gas in the tank I doubt many divers realise they should inspect a tank if has been emptied in this way. It's something I learned from working in the industry and being a sad dive junkie addicted to forums and not from any diver classes or formal training.

Others covered the agencies position, I learned it in my informal scuba class in '62 and again when I certified in '80 (NAUI/PADI class).

The main issue is that the classes now are so short that, except for some major issues, there is no time to reinforce the minor but important points.


Bob

 

[NAM001]

VIP started as a means to protect the tanks from being condemned from pitting vs. anything exploding.

That is very much like PSI operates. fnd any reason to pass but codemn the ones that fail with no question.

 

[BRT]

As stated in other posts I was in error on the -200 it should be -100 and you are also right on how dew point is measured. . while under pressure the RH is always 100% untill chemical drying is imposed.. It can not physically be less. as pressure goes up so does the ability of the air to release water. water removal (mechanical) uses this pressure to ring out the moisture. when it stops coming out you are at 99.999% RH. As psi goes up you ge more water removed. the dew point is a measurement in temperature that will cause the same condensation under standard 1 atm. with out your x13 you will never rerach -100. chemical drying takes over where mechanical stops. -70 is dry enough indeed. the higher the PMV setting the more mechanical drying occures. The more x-13 ,,,, the more chemical drying occurs. filtering after teh x-13 needs to be less than -50 to work properly. I read somewhere 100% rh is 2.5 - 3% by volumn water in the air. and if you pressure the 100% rh air to 10 atm you will remove 90% of the moisture. leaving when returned to 1ATM will mow be 10% rh. That is why after exposing my tanks insides to room air. I fill to perhaps 1000 psi and vent a couple of times. the blending of the 60% rh air in the tank and the compressor DRYER air pretty well removes any untreated atmosphere contaminants from the tank. I have not read the x-13 stuff for a while so i dont know if to get it you have to have a PMV set to 3500 or what ever. No matter what teh output of hte X-13 will be a dwell issue. teh higher teh PMV the drier teh air enter ing teh x-13 bed. normally the Pmv is set to a presure that allows the compressor to run physically ballanced on all stages. I think my rix calls for 1900 psi. and perhaps the bauer at 2500 or so. Quite often i see recommendations of 2800 to max the mechanical condensing. 2800 may be highfor teh ballancing but teh pv only is in play till the tank psi exceeds it. I have seen many configurations using many PVM's one on the compressor output to minimize the start up banging of the last stage floating piston. another the final moisture separator output. and another after each moisture filter stack. even then the use varies if yo are using dedicated stacks or combo stacks. most of us use combo stacks. desicant carbon and perhaps monoxicon.

There is a lot of difference between a -70f and a -80f dew point. -70F returns a dew point of 23F at 3500 psi. A -80F dew point returns a 8F dew point at 3500 psi. One I can live with, one will give me problems. I kept getting little rust spots on the bottom of my tanks. Finally realized that transporting them in temperatures below 20F could do that. I added a section of coiled stainless line in a refrigerated glycol filled tank after the compressor and I feel it made a difference. I have to be careful not to drop the glycol down to 32F because ice forms in the line and no air comes out.

 

[NAM001]

There is a lot of difference between a -70f and a -80f dew point. -70F returns a dew point of 23F at 3500 psi. A -80F dew point returns a 8F dew point at 3500 psi. One I can live with, one will give me problems. I kept getting little rust spots on the bottom of my tanks. Finally realized that transporting them in temperatures below 20F could do that. I added a section of coiled stainless line in a refrigerated glycol filled tank after the compressor and I feel it made a difference. I have to be careful not to drop the glycol down to 32F because ice forms in the line and no air comes out.

I should have said that -70 is good enough for the chemical filtering to work. sorry

 

[TrimixToo]

You can find an online dew point calculator. -65 isn't low enough for me as I may transport filled tanks well below 20 F.

OK...where did I say -65 should be OK for you (or for me)? Scratching head...

 

[TrimixToo]

There is a lot of difference between a -70f and a -80f dew point. -70F returns a dew point of 23F at 3500 psi. A -80F dew point returns a 8F dew point at 3500 psi. One I can live with, one will give me problems. I kept getting little rust spots on the bottom of my tanks. Finally realized that transporting them in temperatures below 20F could do that. I added a section of coiled stainless line in a refrigerated glycol filled tank after the compressor and I feel it made a difference. I have to be careful not to drop the glycol down to 32F because ice forms in the line and no air comes out.

Ah, there's the difference. My diving is all with LP tanks even for my infrequent winter dives. I can tolerate a significantly higher dew point at (ahem) 2640-ish PSI (or, more usual for for my winter dives, 2475-ish PSI) than you can at 3500.

 

[BRT]

Ah, there's the difference. My diving is all with LP tanks even for my infrequent winter dives. I can tolerate a significantly higher dew point at (ahem) 2640-ish PSI (or, more usual for for my winter dives, 2475-ish PSI) than you can at 3500.

Yep. but I think there is a lot of air pumped that is -50 or so.