Wow! Meg design - dont know if I like this

sensor330 · 27th April 2007, 23:30

Quote: (Originally Posted by Drmike)

um the membrane lets gas through otherwise how would the sensor work?

But anyway the membrane comes away with the sensor body (see prev drawing) leaving just a hole.

Yeah your right I shouldn't post so early in the morning ,brain hasn't started working yet. Although the if membrane remained there it would probably stop a full blown shit show. If I'm not getting the correct reading from one of the cell I'll terminate the dive but if the membrane breaks away with the top half it's irrelevant anyway because you'll be a full blown shit show in a matter or minutes.

tecdivertraining · 28th April 2007, 02:21

Quote: (Originally Posted by RonMicjan)

excerpt from meg checklist...

<snip>
____ 16. Inspect sensors and sensor wires.
____ 17. Install sensor moisture pad.
____ 18. Install sensor carriage assembly.
____ 19. Positive pressure test sensor carriage assembly (one-way water check valve).
____ 20. Negative pressure test sensor carriage assembly.
____ 21. Inspect lid assembly for waterproof integrity (O-rings, and all fixed components).
<snip>

item 16 covers actually looking at sensors, verifying they are snug in the threads, thier molex plugs, plug covers, the wires leading to them and one should notice if they are visibly cracked, wouldnt one?

19 and 20 are positive and negative tests on the sensor carriage only (not the whole loop, that comes later) and this test will uncover any bypass problems, whether they are o ring or cell body related. I have heard of zero problems in this regard, other than 2 misassembly issues and the next design change will address that.

I know mike and know he is very experienced, but I think this just reaffirms the need for crossover training that is rig specific. Mike, unless you do the training and learn the nuts and bolts of every item on the checklist, I suggest you dont dive the rig. (not saying this was your intention)

The checklist is a reminder of all the things one has to do when preparing the rig, it is NOT a comprehensive list, otherwise it would be 4 pages long. There are little sub items that fall under each item that are taught as part of the course. The first time anyone puts the meg together as a student it takes about 4 hours to cover the checklist. (no kidding!) but after some experience it comes down to about 18-30 minutes. I do a complete setup in 18 minutes pretty consistantly.

the pressure across the sensors during diving is minimal, just the resistance of the scrubber material, I dont have the numbers, but its way less than the failure spec of the sensor and less than the positive and negative carriage check will put across them. there is no temperature difference from front to back side as the gas is moving between those two points in a matter of one breath and it will heat evenly in a few minutes of diving.

why the question of moisture on cells? In 250 hours of diving I have not had a single problem with that. Divers attitude in water, the moisture channel around the base of cells and the moisture pad all serve to prevent that problem. I dive in very cold to tropical water and no cell face moisture problems.

Ron your above post is spot on But I still see certified divers having completed the ISC check list at the centre not really perform a good pre-dive check prior to jumping in.

On a recent course I gave my three student a homework assignment to produce a good pre-dive check list they could use, one of them came up with the 3'm for MACHINE - ME - MATE (Buddy) I am happy to email it to users if they think it would be useful( I tried to upload it but my mac is having problems) its just a good way of checking common failures that could have occurred during transportation prior to the dive site and addresses some issues when diving with OC buddies.

Mathew@tecdivertraining.com

Cheers

SteveL · 28th April 2007, 09:05

Guys I dont dive a MEG but if the drawings Mike did are representative then the cells are inside the loop so how would a pos / neg test show a failure of this nature ???

If a cell did break off then there is a path for CO2 to bypass the scrubber I agree, but I cant see how a P/N test shows this up.

I am a G&T down + 3/4 bottle Cardy - so might be missing something -

S

***schford*** · 28th April 2007, 09:36

You do a test on JUST the head before you plumb it into the Loop.

Stuart

SteveL · 28th April 2007, 11:25

Quote: (Originally Posted by schford)

You do a test on JUST the head before you plumb it into the Loop.

Stuart

That would explain it then -thanks

S

Gibbon · 28th April 2007, 11:39

Quote: (Originally Posted by schford)

You do a test on JUST the head before you plumb it into the Loop.

Stuart

I guess it is just lucky that although Teledyne do not specify that their cells can cope with a pressure differencial across them in reality their cells can cope with a BAR or so

Has anyone actually tested how destructive pressure is across teledyne cells?

***schford*** · 28th April 2007, 14:31

I am probably being slow but why would the location at each end of the scrubber be at a different pressure?

Temperature difference I can see as cold o2 comes in cools gas down then gas goes through scrubber which warms up gas....

mverick · 28th April 2007, 14:32

Quote: (Originally Posted by schford)

I am probably being slow but why would the location at each end of the scrubber be at a different pressure?

Temperature difference I can see as cold o2 comes in cools gas down then gas goes through scrubber which warms up gas....

The air has to pass through the scrubber material. Giving a very slight back pressure. The differential is there. But it's minimal...

**UWSojourner** · 28th April 2007, 15:06

Quote: (Originally Posted by mverick)

The air has to pass through the scrubber material. Giving a very slight back pressure. The differential is there. But it's minimal...

The pressure will be very small. The pressure of the predive test itself will be large relative to the actual dive pressure. If the cells are that delicate I would think the predive test would provide some possibility for damaging the cells.

**wedivebc** · 28th April 2007, 16:49

Quote: (Originally Posted by Gibbon)

I guess it is just lucky that although Teledyne do not specify that their cells can cope with a pressure differencial across them in reality their cells can cope with a BAR or so

Has anyone actually tested how destructive pressure is across teledyne cells?

I knew this girl in Halifax once who could suck start a diesel engine but in most cases the pressure involved is pretty low.

27th April 2007, 23:30	#41 (permalink)
sensor330 Custom Title Allowed! Current Rebreather/s: Megalodon Other Rebreather/s: Not Bought Yet Inspiration Classic Join Date: Feb 2005 Location: Victoria, British Columbia, Canada Posts: 585	Re: Wow! Meg design - dont know if I like this Quote: (Originally Posted by Drmike) um the membrane lets gas through otherwise how would the sensor work? But anyway the membrane comes away with the sensor body (see prev drawing) leaving just a hole. Yeah your right I shouldn't post so early in the morning ,brain hasn't started working yet. Although the if membrane remained there it would probably stop a full blown shit show. If I'm not getting the correct reading from one of the cell I'll terminate the dive but if the membrane breaks away with the top half it's irrelevant anyway because you'll be a full blown shit show in a matter or minutes.
(Offline)

28th April 2007, 02:21	#42 (permalink)
tecdivertraining RebreatherWorld Sponsor Current Rebreather/s: Inspiration Classic Inspiration Vision Evolution Megalodon Ouroboros Dolphin Other Rebreather/s: Not Bought Yet Dolphin Join Date: May 2005 Location: Phuket, Thailand Posts: 462	Re: Wow! Meg design - dont know if I like this Quote: (Originally Posted by RonMicjan) excerpt from meg checklist... <snip> ____ 16. Inspect sensors and sensor wires. ____ 17. Install sensor moisture pad. ____ 18. Install sensor carriage assembly. ____ 19. Positive pressure test sensor carriage assembly (one-way water check valve). ____ 20. Negative pressure test sensor carriage assembly. ____ 21. Inspect lid assembly for waterproof integrity (O-rings, and all fixed components). <snip> item 16 covers actually looking at sensors, verifying they are snug in the threads, thier molex plugs, plug covers, the wires leading to them and one should notice if they are visibly cracked, wouldnt one? 19 and 20 are positive and negative tests on the sensor carriage only (not the whole loop, that comes later) and this test will uncover any bypass problems, whether they are o ring or cell body related. I have heard of zero problems in this regard, other than 2 misassembly issues and the next design change will address that. I know mike and know he is very experienced, but I think this just reaffirms the need for crossover training that is rig specific. Mike, unless you do the training and learn the nuts and bolts of every item on the checklist, I suggest you dont dive the rig. (not saying this was your intention) The checklist is a reminder of all the things one has to do when preparing the rig, it is NOT a comprehensive list, otherwise it would be 4 pages long. There are little sub items that fall under each item that are taught as part of the course. The first time anyone puts the meg together as a student it takes about 4 hours to cover the checklist. (no kidding!) but after some experience it comes down to about 18-30 minutes. I do a complete setup in 18 minutes pretty consistantly. the pressure across the sensors during diving is minimal, just the resistance of the scrubber material, I dont have the numbers, but its way less than the failure spec of the sensor and less than the positive and negative carriage check will put across them. there is no temperature difference from front to back side as the gas is moving between those two points in a matter of one breath and it will heat evenly in a few minutes of diving. why the question of moisture on cells? In 250 hours of diving I have not had a single problem with that. Divers attitude in water, the moisture channel around the base of cells and the moisture pad all serve to prevent that problem. I dive in very cold to tropical water and no cell face moisture problems. Ron your above post is spot on But I still see certified divers having completed the ISC check list at the centre not really perform a good pre-dive check prior to jumping in. On a recent course I gave my three student a homework assignment to produce a good pre-dive check list they could use, one of them came up with the 3'm for MACHINE - ME - MATE (Buddy) I am happy to email it to users if they think it would be useful( I tried to upload it but my mac is having problems) its just a good way of checking common failures that could have occurred during transportation prior to the dive site and addresses some issues when diving with OC buddies. Mathew@tecdivertraining.com Cheers __________________ Mathew Partridge Technical Director Pro-Tech Dive College www.protechdivers.com www.tech-ccr.com
(Offline)

28th April 2007, 09:05	#43 (permalink)
SteveL Custom Title Allowed! Current Rebreather/s: MK 15.X Other Rebreather/s: Inspiration Classic Join Date: Nov 2005 Location: Sydney Australia Posts: 222	Re: Wow! Meg design - dont know if I like this Guys I dont dive a MEG but if the drawings Mike did are representative then the cells are inside the loop so how would a pos / neg test show a failure of this nature ??? If a cell did break off then there is a path for CO2 to bypass the scrubber I agree, but I cant see how a P/N test shows this up. I am a G&T down + 3/4 bottle Cardy - so might be missing something - S
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28th April 2007, 09:36	#44 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,562	Re: Wow! Meg design - dont know if I like this You do a test on JUST the head before you plumb it into the Loop. Stuart __________________ Bailout and Kit Management account for Murphy's Law The only bad question is one you did not ask and later wish you had. Use of Rebreather World is subject to the Rebreather World Terms & Conditions of Use
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28th April 2007, 11:25	#45 (permalink)
SteveL Custom Title Allowed! Current Rebreather/s: MK 15.X Other Rebreather/s: Inspiration Classic Join Date: Nov 2005 Location: Sydney Australia Posts: 222	Re: Wow! Meg design - dont know if I like this Quote: (Originally Posted by schford) You do a test on JUST the head before you plumb it into the Loop. Stuart That would explain it then -thanks S
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28th April 2007, 11:39	#46 (permalink)
Gibbon Southern Monkey Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2005 Location: East Devon Posts: 224	Re: Wow! Meg design - dont know if I like this Quote: (Originally Posted by schford) You do a test on JUST the head before you plumb it into the Loop. Stuart I guess it is just lucky that although Teledyne do not specify that their cells can cope with a pressure differencial across them in reality their cells can cope with a BAR or so Has anyone actually tested how destructive pressure is across teledyne cells?
(Offline)

28th April 2007, 14:31	#47 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,562	Re: Wow! Meg design - dont know if I like this I am probably being slow but why would the location at each end of the scrubber be at a different pressure? Temperature difference I can see as cold o2 comes in cools gas down then gas goes through scrubber which warms up gas.... __________________ Bailout and Kit Management account for Murphy's Law The only bad question is one you did not ask and later wish you had. Use of Rebreather World is subject to the Rebreather World Terms & Conditions of Use
(Offline)

28th April 2007, 14:32	#48 (permalink)
mverick ScubaPimp Current Rebreather/s: Megalodon Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Aug 2005 Posts: 545	Re: Wow! Meg design - dont know if I like this Quote: (Originally Posted by schford) I am probably being slow but why would the location at each end of the scrubber be at a different pressure? Temperature difference I can see as cold o2 comes in cools gas down then gas goes through scrubber which warms up gas.... The air has to pass through the scrubber material. Giving a very slight back pressure. The differential is there. But it's minimal...
(Online)

28th April 2007, 15:06	#49 (permalink)
UWSojourner Pacific Northwest Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Portland Oregon Posts: 556	Re: Wow! Meg design - dont know if I like this Quote: (Originally Posted by mverick) The air has to pass through the scrubber material. Giving a very slight back pressure. The differential is there. But it's minimal... The pressure will be very small. The pressure of the predive test itself will be large relative to the actual dive pressure. If the cells are that delicate I would think the predive test would provide some possibility for damaging the cells.
(Offline)

28th April 2007, 16:49	#50 (permalink)
wedivebc Dave Tomblin Current Rebreather/s: Megalodon Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Other CCR Join Date: Feb 2005 Location: Vancouver Island BC Canada Posts: 1,444	Re: Wow! Meg design - dont know if I like this Quote: (Originally Posted by Gibbon) I guess it is just lucky that although Teledyne do not specify that their cells can cope with a pressure differencial across them in reality their cells can cope with a BAR or so Has anyone actually tested how destructive pressure is across teledyne cells? I knew this girl in Halifax once who could suck start a diesel engine but in most cases the pressure involved is pretty low. __________________ Cheers, Dave.... Man is the only animal burdened with the knowledge he will eventually die
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