Wob

mmcauliffe · 8th July 2008, 18:32

Ok, I don't even have my first breather yet (pick it up this Thursday) and no training, (starts next week) so this may be a stupid question but....

I've been reading a little about WOB and how it does (or could) be a contributor to CO2, so....

Why does the breathing hoses/loops have a corrugated I.D.? I assume the ribs on the exterior add necessary rigidity to the loop/hose so they won't collapse but why can't the I.D. be smooth or even lined with a slick material like Teflon?

I'll take a stab at answering my own question, does it have something to do with wanting to create turbulence and helping to mix the O2 with Dil as it travels down the hose?

**aainslie** · 8th July 2008, 18:39

Happy birthday again, Mike!

Corrugated hoses shorten up normally, but allow you to extend them when needed e.g. getting in and out of kit, or stretching the hose above your head to get water out.

Most of the WOB comes from the scrubber and the mouthpiece, I suspect. Others with more expertise can comment.

David Pye · 8th July 2008, 18:45

Quote: (Originally Posted by mmcauliffe)

<snip>

Why are the loops of a corrugated design internally? I assume the ribs on the exterior add necessary rigidity to the loop/hose but why can't the I.D. be smooth or even lined with a slick material like Teflon?

I'll take a stab at answering my own question, does it have something to do with helping to mix the O2 with Dil?

Doesn't sound like a stupid question to me!

Nah, I don't think that mixing O2 and diluent is a problem.

It's more manufacturing simplicity and weight, as I understand it. Cooper hoses do have smoother linings, but as DrMike found out recently, add another failure mode as they have a wire-supported outer and a thin smooth inner lining.

David

**Gill Envy** · 8th July 2008, 19:22

I think Andrew hit the nail on the head, it's flexibility. You need to be able to turn your head and move around without kinking the hose.

As for WOB and the meg, if your unit comes with the same mouth piece mine did, i'd highly recommend binning it and getting a thicker one that separates your teeth more. here's a thread I started on the subject: http://www.rebreatherworld.com/rebre...tml#post196713
g

Quote: (Originally Posted by aainslie)

Happy birthday again, Mike!

Corrugated hoses shorten up normally, but allow you to extend them when needed e.g. getting in and out of kit, or stretching the hose above your head to get water out.

Most of the WOB comes from the scrubber and the mouthpiece, I suspect. Others with more expertise can comment.

dave t · 8th July 2008, 21:43

Smooth hoses on the inside would indeed improve WOB but its a trade off, corrugated hoses are more flexible and versitle.

Anything that impeds gas flow will have an impact on WOB and corrugations will cause turbulance, but if the rest of the loop is well designed its effect is minimal

Dave

Celia_E · 8th July 2008, 23:12

Yep, flexibility and it also helps keeping them from kinking since they are low pressure and would not keep their shape easily (that last one is my personal guess...)

As far as WOB, well, that is why they have such large diameters too....

Dive safe,

Celia

PCDiver · 9th July 2008, 06:43

What about a hose that is smooth on the inside but with the reinforcements on the outside?

Drmike · 9th July 2008, 07:50

Quote: (Originally Posted by PCDiver)

What about a hose that is smooth on the inside but with the reinforcements on the outside?

this is how copper hoses work. the linner is smooth the 'corrogation' is actually the cloth covered wire

I dont think at these flow rates the corrogations add any significant loss

for good wob what you want is

large hose dia and large bend radii

which can translate to long hoses.....which is likely why boris and sentinel hoses were selected to be long (as well as making them very comfortable - load wise when turning head, more comfortable than my other units)

many people push for small everything. small units, small hoses, small dsvs, small bov, - but in the world of fluid dynamics small often translates to higher resistance to flow = higher wob

8th July 2008, 18:32	#1 (permalink)
mmcauliffe New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Jun 2008 Location: Cave Country, Luraville Florida Posts: 58	Wob Ok, I don't even have my first breather yet (pick it up this Thursday) and no training, (starts next week) so this may be a stupid question but.... I've been reading a little about WOB and how it does (or could) be a contributor to CO2, so.... Why does the breathing hoses/loops have a corrugated I.D.? I assume the ribs on the exterior add necessary rigidity to the loop/hose so they won't collapse but why can't the I.D. be smooth or even lined with a slick material like Teflon? I'll take a stab at answering my own question, does it have something to do with wanting to create turbulence and helping to mix the O2 with Dil as it travels down the hose? Last edited by mmcauliffe : 8th July 2008 at 22:13. Reason: changed wording to clarify my question
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8th July 2008, 18:39	#2 (permalink)
aainslie So Cal Tech Diver Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Apr 2006 Location: LA Posts: 197	Re: Wob Happy birthday again, Mike! Corrugated hoses shorten up normally, but allow you to extend them when needed e.g. getting in and out of kit, or stretching the hose above your head to get water out. Most of the WOB comes from the scrubber and the mouthpiece, I suspect. Others with more expertise can comment. __________________ Andrew Ainslie
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8th July 2008, 18:45	#3 (permalink)
David Pye CK#69 Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: May 2006 Location: Newcastle Upon Tyne Posts: 175	Re: Wob Quote: (Originally Posted by mmcauliffe) <snip> Why are the loops of a corrugated design internally? I assume the ribs on the exterior add necessary rigidity to the loop/hose but why can't the I.D. be smooth or even lined with a slick material like Teflon? I'll take a stab at answering my own question, does it have something to do with helping to mix the O2 with Dil? Doesn't sound like a stupid question to me! Nah, I don't think that mixing O2 and diluent is a problem. It's more manufacturing simplicity and weight, as I understand it. Cooper hoses do have smoother linings, but as DrMike found out recently, add another failure mode as they have a wire-supported outer and a thin smooth inner lining. David
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8th July 2008, 19:22	#4 (permalink)
Gill Envy Shearwater Copis Divers Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,314	Re: Wob I think Andrew hit the nail on the head, it's flexibility. You need to be able to turn your head and move around without kinking the hose. As for WOB and the meg, if your unit comes with the same mouth piece mine did, i'd highly recommend binning it and getting a thicker one that separates your teeth more. here's a thread I started on the subject: http://www.rebreatherworld.com/rebre...tml#post196713 g Quote: (Originally Posted by aainslie) Happy birthday again, Mike! Corrugated hoses shorten up normally, but allow you to extend them when needed e.g. getting in and out of kit, or stretching the hose above your head to get water out. Most of the WOB comes from the scrubber and the mouthpiece, I suspect. Others with more expertise can comment. __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°> Last edited by Gill Envy : 8th July 2008 at 20:45.
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8th July 2008, 21:43	#5 (permalink)
dave t Custom Title Allowed! Current Rebreather/s: Inspiration Classic Inspiration Vision Evolution Sport Kiss Classic Kiss Dolphin Ray Azimuth Home Build Other Rebreather/s: Dolphin Ray Azimuth Home Build Join Date: May 2005 Location: UK Posts: 654	Re: Wob Smooth hoses on the inside would indeed improve WOB but its a trade off, corrugated hoses are more flexible and versitle. Anything that impeds gas flow will have an impact on WOB and corrugations will cause turbulance, but if the rest of the loop is well designed its effect is minimal Dave
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8th July 2008, 23:12	#6 (permalink)
Celia_E Custom Title Allowed! Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Nov 2006 Location: back from paradise... Posts: 107	Re: Wob Yep, flexibility and it also helps keeping them from kinking since they are low pressure and would not keep their shape easily (that last one is my personal guess...) As far as WOB, well, that is why they have such large diameters too.... Dive safe, Celia __________________ "We are now a two Meg family!!!"
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9th July 2008, 06:43	#7 (permalink)
PCDiver Submerge Productions Current Rebreather/s: Inspiration Vision Other Rebreather/s: Inspiration Classic Join Date: Feb 2005 Location: Belgium Posts: 969	Re: Wob What about a hose that is smooth on the inside but with the reinforcements on the outside? __________________ >>>>> www.submergeproductions.com dedicated to promoting technical diving >>>>> Check out our dive show video interviews and Wreck dive videos >>>>> Now also on iTunes and Zune
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9th July 2008, 07:50	#8 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,323	Re: Wob Quote: (Originally Posted by PCDiver) What about a hose that is smooth on the inside but with the reinforcements on the outside? this is how copper hoses work. the linner is smooth the 'corrogation' is actually the cloth covered wire I dont think at these flow rates the corrogations add any significant loss for good wob what you want is large hose dia and large bend radii which can translate to long hoses.....which is likely why boris and sentinel hoses were selected to be long (as well as making them very comfortable - load wise when turning head, more comfortable than my other units) many people push for small everything. small units, small hoses, small dsvs, small bov, - but in the world of fluid dynamics small often translates to higher resistance to flow = higher wob __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by Drmike : 9th July 2008 at 07:59.
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