materials for rebreather construction

OceanOpportunity · 17th January 2007, 23:32

Hey all,

Does anyone have any specific materials science or other technical references referring to the use of PVC for rebreather components? info on reactivity with various gasses, under pressure, with CaOH rxn's, etc?

thanks.

montyg · 18th January 2007, 04:44

Hi

While I dont have exactly what you asked for (tech specs & MSDS), may I suggest that you consider other properties of PVC aside from chemical resistance? (i.e. the fact that it's not as strong at low temperatures)

HTH

rgds
monty

whoizrob · 18th January 2007, 18:09

If you do a search you should find them.. it wasn't too long ago if I remember correctly. One of my bigger concerns would be the PVC off gassing nasty chemicals into the loop. Just a thought...

Rob

Crazyduck · 18th January 2007, 19:47

You might want to refer to the following:
Link:
http://www.ndc.noaa.gov/pdfs/NOAA%20...al%20Draft.pdf

Section 2.21 (page 4 of 9)
Talks directly to PVC topic.

I would start doing a seach on PVC and NEDU and see what pops up.

Regards, Andrew

Genesis · 19th January 2007, 02:30

Be careful that you look at the "correct" PVC grade.

There's more than one.

Specifically, there are grades of PVC that are considered drinking-water safe - that is, they do not offgas into the water conducted through them, and thus the US government (at least) considers it safe to drink water conducted through those pipes. Note that drinking water pipes may have water "held" in them for a relatively long period of time (e.g. days) before being withdrawn and consumed.

I personally am comfortable with using those grades of PVC, as if they don't offgas into conducted water, it is reasonable to presume they would not do so materially into air in them. This does NOT apply to those which are designated "DWW" (e.g. drain pipe) or similar.

And again - this is my personal view on the matter (there are some PVC components in my K1 homebuild)

The document referenced above speaks to PVC coatings, which of course are distinct from solid PVC extrusions (e.g. pipe)

There are of course other material properties to be concerned with, as has been noted, especially under very cold conditions. One must consider whether or not environmental conditions that could lead to trouble are going to be encountered by the device.

OceanOpportunity · 19th January 2007, 21:22

I am VERY familiar with the NOAA doc referenced, as I was one of the independent reviewers during its first cut several years ago. I think there has been a stigma attached to the use of PVC due to the off-gassing issue, but as Karl stated, the grades of PVC generally suitable for water storage are effective. Also, PVC is used in alot of medical breathing bags/non-rebreather masks. The temperature concern is obviously simple enough to address (i.e. dont use it in freezing temps), but the specs I've read make it suitable for the normal ranges of temps experienced in temperate to tropical climates.

PVC is a very durable material, easily machinable, inexpensive, and readily available...so I'm digging deep for specific data or publications referencing data that would deter my efforts. If its out there, please pass along..I can't find any, other than the general comments in line with the stigma.

thanks for the help!

Crazyduck · 19th January 2007, 21:48

Sorry, I am far from am expert.

I have read a few things on PVC and Navy comments.
However, the guys in “homebuilt rebreathers” have made and use a series of PVC products and they seem very interesting.

PVC seems to cause the biggest problems in scrubbers with the temperature issues and other factors. I like LEXAN, Delrin, HDPE or an Ultra Density Delrin as good options.

I personally like LEXAN- that’s what’s sitting at home calling my name for a simple small- scrubber can. Plus, it does not shatter like Acrylic.

Aluminum, I think could work well- but when we use Aluminum at work for harsh environment or wash down environments we have it hard anodized and then Teflon coated.

There are other processes and materials but some are very expensive and I really don’t want to breathe into beryllium cooper. (Yuck….) that was a joke….

This looks like a very interesting book-
Link- http://www.bestpub.com/bookstore2.asp
Book title- LIFE SUPPORT SYSTEMS DESIGN
M.L. Nuckols, Ace J. Sarich and Wayne C. Tucker

Good luck
Best Regards, Andrew

PS- is it your group that took over the CCR2000?

OceanOpportunity · 19th January 2007, 22:23

Hello Andrew,

we were involved with the CCR2000 project for only a brief time in 2003/2004. I am not sure what its current status is, but I know that the website is still up Scuba Diving Rebreather Underwater Closed Circuit Rebreather.

Our current project is an academic-driven collaboration involving student researchers from MIT and the Univ of Rhode Island, along with a corporate partner. We anticipate a website launch within 2007 sometime. The unit will not be going into production, rather used as a research tool and platform gor ongoing rebreather R&D.

DepthCharge · 19th January 2007, 22:30

Quote: (Originally Posted by Crazyduck)

Sorry, I am far from am expert.

I personally like LEXAN- that’s what’s sitting at home calling my name for a simple small- scrubber can. Plus, it does not shatter like Acrylic.

You might want to look into how Lexan reacts with alkalines before you try it out. Not very favorably IIRC Acrylic is a better choice believe it or not

marekm · 20th January 2007, 20:07

In regards to lexan (polycarbonate plastic) and alkaline solutions (such as caustic cocktail), from my own tests I have found that lexan starts to deteriorate after about one month of constant contact with a 1M NaOH solution. So you could still use a lexan scubber canister but don't expect it to last forever, especially if you get some flooding of the lime.

-Marek

17th January 2007, 23:32	#1 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 517	materials for rebreather construction Hey all, Does anyone have any specific materials science or other technical references referring to the use of PVC for rebreather components? info on reactivity with various gasses, under pressure, with CaOH rxn's, etc? thanks.
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18th January 2007, 04:44	#2 (permalink)
montyg Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Feb 2007 Location: Cape Town, South Africa Posts: 223	Re: materials for rebreather construction Hi While I dont have exactly what you asked for (tech specs & MSDS), may I suggest that you consider other properties of PVC aside from chemical resistance? (i.e. the fact that it's not as strong at low temperatures) HTH rgds monty
(Online)

18th January 2007, 18:09	#3 (permalink)
whoizrob New Member Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Apr 2006 Location: Sacramento Posts: 72	There have been some good threads on material selection... If you do a search you should find them.. it wasn't too long ago if I remember correctly. One of my bigger concerns would be the PVC off gassing nasty chemicals into the loop. Just a thought... Rob
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18th January 2007, 19:47	#4 (permalink)
Crazyduck Underwater Mechanic Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Mar 2005 Location: TEXAS, Dallas/ Ft.Worth Posts: 704	Re: materials for rebreather construction You might want to refer to the following: Link: http://www.ndc.noaa.gov/pdfs/NOAA%20...al%20Draft.pdf Section 2.21 (page 4 of 9) Talks directly to PVC topic. I would start doing a seach on PVC and NEDU and see what pops up. Regards, Andrew __________________ Howdy Senor- What’s Happening! Rob Davie April 2005- Presently in a state of transition from Open Circuit to Closed Circuit. "You will not be punished for your anger; you will be punished by it." - Buddha.
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19th January 2007, 02:30	#5 (permalink)
Genesis Bubbless Box of Death Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Oct 2005 Location: Sunny Florida Posts: 1,394	Re: materials for rebreather construction Be careful that you look at the "correct" PVC grade. There's more than one. Specifically, there are grades of PVC that are considered drinking-water safe - that is, they do not offgas into the water conducted through them, and thus the US government (at least) considers it safe to drink water conducted through those pipes. Note that drinking water pipes may have water "held" in them for a relatively long period of time (e.g. days) before being withdrawn and consumed. I personally am comfortable with using those grades of PVC, as if they don't offgas into conducted water, it is reasonable to presume they would not do so materially into air in them. This does NOT apply to those which are designated "DWW" (e.g. drain pipe) or similar. And again - this is my personal view on the matter (there are some PVC components in my K1 homebuild) The document referenced above speaks to PVC coatings, which of course are distinct from solid PVC extrusions (e.g. pipe) There are of course other material properties to be concerned with, as has been noted, especially under very cold conditions. One must consider whether or not environmental conditions that could lead to trouble are going to be encountered by the device. __________________ "A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American." http://www.denninger.net http://www.diversunion.org/liability.htm - Fix the Diving Cert racket
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19th January 2007, 21:22	#6 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 517	Re: materials for rebreather construction I am VERY familiar with the NOAA doc referenced, as I was one of the independent reviewers during its first cut several years ago. I think there has been a stigma attached to the use of PVC due to the off-gassing issue, but as Karl stated, the grades of PVC generally suitable for water storage are effective. Also, PVC is used in alot of medical breathing bags/non-rebreather masks. The temperature concern is obviously simple enough to address (i.e. dont use it in freezing temps), but the specs I've read make it suitable for the normal ranges of temps experienced in temperate to tropical climates. PVC is a very durable material, easily machinable, inexpensive, and readily available...so I'm digging deep for specific data or publications referencing data that would deter my efforts. If its out there, please pass along..I can't find any, other than the general comments in line with the stigma. thanks for the help! __________________ Michael Lombardi Oceans of Opportunity www.oceanopportunity.com Elected Director, Society for Human Performance in Extreme Environments MN'07, The Explorers Club Project Manager, Diving a Dream
(Offline)

19th January 2007, 21:48	#7 (permalink)
Crazyduck Underwater Mechanic Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Mar 2005 Location: TEXAS, Dallas/ Ft.Worth Posts: 704	Re: materials for rebreather construction Sorry, I am far from am expert. I have read a few things on PVC and Navy comments. However, the guys in “homebuilt rebreathers” have made and use a series of PVC products and they seem very interesting. PVC seems to cause the biggest problems in scrubbers with the temperature issues and other factors. I like LEXAN, Delrin, HDPE or an Ultra Density Delrin as good options. I personally like LEXAN- that’s what’s sitting at home calling my name for a simple small- scrubber can. Plus, it does not shatter like Acrylic. Aluminum, I think could work well- but when we use Aluminum at work for harsh environment or wash down environments we have it hard anodized and then Teflon coated. There are other processes and materials but some are very expensive and I really don’t want to breathe into beryllium cooper. (Yuck….) that was a joke…. This looks like a very interesting book- Link- http://www.bestpub.com/bookstore2.asp Book title- LIFE SUPPORT SYSTEMS DESIGN M.L. Nuckols, Ace J. Sarich and Wayne C. Tucker Good luck Best Regards, Andrew PS- is it your group that took over the CCR2000? __________________ Howdy Senor- What’s Happening! Rob Davie April 2005- Presently in a state of transition from Open Circuit to Closed Circuit. "You will not be punished for your anger; you will be punished by it." - Buddha.
(Offline)

19th January 2007, 22:23	#8 (permalink)
OceanOpportunity for a world of water Current Rebreather/s: Other CCR Dolphin Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Other CCR Dolphin Home Build Join Date: Nov 2006 Location: Providence, RI USA Posts: 517	Re: materials for rebreather construction Hello Andrew, we were involved with the CCR2000 project for only a brief time in 2003/2004. I am not sure what its current status is, but I know that the website is still up Scuba Diving Rebreather Underwater Closed Circuit Rebreather. Our current project is an academic-driven collaboration involving student researchers from MIT and the Univ of Rhode Island, along with a corporate partner. We anticipate a website launch within 2007 sometime. The unit will not be going into production, rather used as a research tool and platform gor ongoing rebreather R&D. __________________ Michael Lombardi Oceans of Opportunity www.oceanopportunity.com Elected Director, Society for Human Performance in Extreme Environments MN'07, The Explorers Club Project Manager, Diving a Dream
(Offline)

19th January 2007, 22:30	#9 (permalink)
DepthCharge New Member Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Home Build Join Date: Mar 2005 Location: upstate NY Posts: 229	Re: materials for rebreather construction Quote: (Originally Posted by Crazyduck) Sorry, I am far from am expert. I personally like LEXAN- that’s what’s sitting at home calling my name for a simple small- scrubber can. Plus, it does not shatter like Acrylic. You might want to look into how Lexan reacts with alkalines before you try it out. Not very favorably IIRC Acrylic is a better choice believe it or not __________________ Later, John It's better to beg forgiveness than ask permission
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20th January 2007, 20:07	#10 (permalink)
marekm Banned Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Oct 2006 Location: Brisbane, Australia Posts: 196	Re: materials for rebreather construction In regards to lexan (polycarbonate plastic) and alkaline solutions (such as caustic cocktail), from my own tests I have found that lexan starts to deteriorate after about one month of constant contact with a 1M NaOH solution. So you could still use a lexan scubber canister but don't expect it to last forever, especially if you get some flooding of the lime. -Marek
(Offline)

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