Ok, tear it apart (New Home Build Design)

canetoad · 22nd December 2007, 01:17

Sorry if I didn't make it clear in the previous post; I do realize that PVC parts can offgas dangerous compounds. I know, as well, that some types of PVC are worse than others & that msds info for each can be obtained.
Thanks,
PM

AD_ward9 · 24th December 2007, 07:16

Quote: (Originally Posted by canetoad)

AD_ward9; I have read many of the previous posts about offgassing & do have some concerns. I know a number of others have used PVC with varying degrees of success but I doubt I'll use this unit long term in any case. Actually; there should be no PVC to PVC gluing involved; only rubber to rubber & only if the mechanical seal I have in mind fails.

Thanks,
PM

If you put it into a pressure pot with a viewing port on it, you often see what looks like white smoke come off PVC. It is not just a little bit of offgasing ...

The chemicals involved can give real long term health problems. That is why Greenpeace are trying to ban PVC, and several other plastics.

However, ignore all the long term effects because there are some short term issues here. Breathing loop and seals. Can your describe your seals in more detail? The look like standard PVC plumbing pipe seals with the elastomer ring inside. Those are the ones I referred to in my first post as being unsuitable for diving.

Alex

canetoad · 24th December 2007, 13:14

AD_ward9; Do you have any details as to what pressure, temp, & O2 levels, etc. the white smoke effect occurred? If it occurred @ or near 1.6 ATM ppO2 that would certainly give me pause. Enough that I would likely find a more suitable replacement material.
As regards seals on the scrubber housing; except for the black grating covering the center opening visible in the photos, all seals are PVC to rubber secured with metal hose clamps. The black grating is an interference fit secured by 2 set screws. Also, if it is not clear in the photos, the scrubber housing is all 1 piece.

Thanks,
PM

AD_ward9 · 24th December 2007, 16:21

Quote: (Originally Posted by canetoad)

AD_ward9; Do you have any details as to what pressure, temp, & O2 levels, etc. the white smoke effect occurred? If it occurred @ or near 1.6 ATM ppO2 that would certainly give me pause. Enough that I would likely find a more suitable replacement material.
As regards seals on the scrubber housing; except for the black grating covering the center opening visible in the photos, all seals are PVC to rubber secured with metal hose clamps. The black grating is an interference fit secured by 2 set screws. Also, if it is not clear in the photos, the scrubber housing is all 1 piece.

Thanks,
PM

Offgasing is not burning. It happens at room temperature and independent of the O2 level. Imagine the part in vacuum: gas comes out of it. Now imagine 10 times the pressure differential of a vacuum: that is a dive to 100msw then back to the surface.

Metal hose clamps work fine for sealing. See the HAZOP on our web site (Deep Life Ltd: Design Submission for Open Revolution ) for hoses.

Alex

22nd December 2007, 01:17	#21 (permalink)
canetoad New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Feb 2007 Location: Florida Posts: 30	Re: Ok, tear it apart (New Home Build Design) Sorry if I didn't make it clear in the previous post; I do realize that PVC parts can offgas dangerous compounds. I know, as well, that some types of PVC are worse than others & that msds info for each can be obtained. Thanks, PM __________________ PM
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24th December 2007, 07:16	#22 (permalink)
AD_ward9 RBW Member Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 2,011	Re: Ok, tear it apart (New Home Build Design) Quote: (Originally Posted by canetoad) AD_ward9; I have read many of the previous posts about offgassing & do have some concerns. I know a number of others have used PVC with varying degrees of success but I doubt I'll use this unit long term in any case. Actually; there should be no PVC to PVC gluing involved; only rubber to rubber & only if the mechanical seal I have in mind fails. Thanks, PM If you put it into a pressure pot with a viewing port on it, you often see what looks like white smoke come off PVC. It is not just a little bit of offgasing ... The chemicals involved can give real long term health problems. That is why Greenpeace are trying to ban PVC, and several other plastics. However, ignore all the long term effects because there are some short term issues here. Breathing loop and seals. Can your describe your seals in more detail? The look like standard PVC plumbing pipe seals with the elastomer ring inside. Those are the ones I referred to in my first post as being unsuitable for diving. Alex Last edited by AD_ward9 : 24th December 2007 at 07:19.
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24th December 2007, 13:14	#23 (permalink)
canetoad New Member Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Feb 2007 Location: Florida Posts: 30	Re: Ok, tear it apart (New Home Build Design) AD_ward9; Do you have any details as to what pressure, temp, & O2 levels, etc. the white smoke effect occurred? If it occurred @ or near 1.6 ATM ppO2 that would certainly give me pause. Enough that I would likely find a more suitable replacement material. As regards seals on the scrubber housing; except for the black grating covering the center opening visible in the photos, all seals are PVC to rubber secured with metal hose clamps. The black grating is an interference fit secured by 2 set screws. Also, if it is not clear in the photos, the scrubber housing is all 1 piece. Thanks, PM __________________ PM
(Offline)

24th December 2007, 16:21	#24 (permalink)
AD_ward9 RBW Member Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 2,011	Re: Ok, tear it apart (New Home Build Design) Quote: (Originally Posted by canetoad) AD_ward9; Do you have any details as to what pressure, temp, & O2 levels, etc. the white smoke effect occurred? If it occurred @ or near 1.6 ATM ppO2 that would certainly give me pause. Enough that I would likely find a more suitable replacement material. As regards seals on the scrubber housing; except for the black grating covering the center opening visible in the photos, all seals are PVC to rubber secured with metal hose clamps. The black grating is an interference fit secured by 2 set screws. Also, if it is not clear in the photos, the scrubber housing is all 1 piece. Thanks, PM Offgasing is not burning. It happens at room temperature and independent of the O2 level. Imagine the part in vacuum: gas comes out of it. Now imagine 10 times the pressure differential of a vacuum: that is a dive to 100msw then back to the surface. Metal hose clamps work fine for sealing. See the HAZOP on our web site (Deep Life Ltd: Design Submission for Open Revolution ) for hoses. Alex
(Offline)

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