Ventilation Fan in Loop

Lure_Angler · 19th February 2007, 13:43

Dear all,

It just occur to me:

What would happen if I place a ventilation fan (read: motherboard cooling fans), blowing in the direction of the gas flow in a rebreather's loop?

I reckon we'll probably get better WOB, better scrubbed air since the gas now moves thru the scrubber more times.

we could probably do away with the check valves too = better WOB?

Con: more electronics, one more point of failure. whirring sound from fan scares fish away?

comments pls, thank you.

TC

Sutty · 19th February 2007, 14:39

Museums of old anaesthetic equipment include a "circle" system (i.e. loop with absorber etc, run semi-closed), which used the energy of gas injection to help circulate the gas around the loop. Long since abandoned, interesting as the WOB of current circle systems is awful (I tried breathing on one).

Problems with your idea include:

1. Electric fan in a condensing atmosphere
2. Probably still need valves in case of failure
3. If fan fails will increase WOB compared to no fan
4. Might need to monitor gas flow in the loop to confirm operation

However there could be some mileage in powered gas movement for very deep dives with high gas densities in the loop. Not sure I'd fancy testing it though!

Neil

divetheworld · 19th February 2007, 14:45

Quote: (Originally Posted by Lure_Angler)

I reckon we'll probably get <snip> better scrubbed air since the gas now moves thru the scrubber more times.
comments pls, thank you.

TC

Potential for the opposite. Think dwell time........

AD_ward9 · 19th February 2007, 14:51

Some tit bits that may help, from someone who has actually done this for a very deep rebreather:

1. Each blade of a fan, such as a computer fan, can develop around 4mbar of pressure differential across it, due to their low speed (they have a small diameter, so linear speeds compared to an aircraft propeller, is low and the area involved is small). The blades do work more efficiently at depth, increasing linearly with pressure in ATM, but 3 times less efficiently in helium.

2. You can increase the pressure by stacking blades like a turbine. If you are trying to reduce the WOB, then it is probably because the WOB is too high. This means you are probably going for a reduction in breathing resistance in excess of 25mbar (the EN14143:2003 breathing resistance limit). That requires 8 or so blades. An 8 blade compressor is noisy.

3. Fans contain PVC and volatile greases.

4. Doing this with optimal control causes the inhale counterlung to be always full, and the counterlung to be always empty when balanced, and when not, both counterlungs are full.

5. There are better ways to achieve reductions in WOB. You do not describe what your reasons are: is it a bad design of rebreather or that you want to dive where no man has gone before on SCUBA?

Alex

Quote: (Originally Posted by Lure_Angler)

Dear all,

It just occur to me:

What would happen if I place a ventilation fan (read: motherboard cooling fans), blowing in the direction of the gas flow in a rebreather's loop?

I reckon we'll probably get better WOB, better scrubbed air since the gas now moves thru the scrubber more times.

we could probably do away with the check valves too = better WOB?

Con: more electronics, one more point of failure. whirring sound from fan scares fish away?

comments pls, thank you.

TC

**Dave Sutton** · 19th February 2007, 19:18

[quote=Lure_Angler;97324]whirring sound from fan scares fish away? /quote]

No, just the odd diver who is afraid of being blown up in an 02 fire with a motor running in a high PP02 environment. Not only is this an idea that has no value from any performance standpoint, it is frankly dangerous. Hyperbaric environments with high PP02 potentials are always a fireproof environment, lighting is a hyperbaric chamber is done with fiber optic tubes (no electrics in the chamber), heating is done with water heat exchangers, fans are run remotely thru magnetic drives, etc. NO MOTORS would ever be allowed... and a rebreather loop ought to be handled the same way. There is no problem to solve here, so why make one up?

Dive more. Dream less.

Dave

AD_ward9 · 19th February 2007, 19:27

Dave, I would differ on the issue of O2 compatibility here.

A decent fan has a DC brushless direct drive motor. What is the reason for it not being in the loop?

The windings are copper. Copper is a highly O2 compatible material.
The blades of the fan are coated aluminium, as is the fan frame. For a PPO2 of only 1.3, that is fine.
The iron armature may be nickel plated, but in any case is protected from the gas stream. Davy Lamp principle applies - only slight pun intended: Sir Humphry Davy invented it in 1816 and saved very many lives.
The problem is the bearings: the grease has to be replaced, but that is fairly simple.
The PVC has to be replaced: it is the wires from the windings. That is fairly simple again, replacing with Kynar covered multistrand plated wire.

Where is the O2 hazard?

I am not saying the fan is the way to do this, but the issue is not one of O2 compatibility, if properly executed. They are instead the practical issues: noise, size, power, control.

It is also not a dream: Manned underwater rebreather dives to 450msw have been carried out in the sea with one of the breathing assistance systems that has been developed (not ours, alas, so far). It is a real issue for diving in places such as off of Brazil, where dives to 300m are carried out daily. Not many rebreathers work well at 300m. Or 600m. These are quite serious dives. There is a need for breathing assistance in rebreathers for this sort of stuff and at least three companies have units that do just that, or try to. I do not suggest for a moment, the divers on this thread had in mind such dives, but that is where breathing assistance has its application. Some caves dives could also benefit from these systems.

Incidentally, if the fan/piston/bellows shift the same amount of air as your lungs, then the scrubber dwell time is not affected. This control is not trivial.

Alex
[quote=Dave Sutton;97394]

Quote: (Originally Posted by Lure_Angler)

whirring sound from fan scares fish away? /quote]

No, just the odd diver who is afraid of being blown up in an 02 fire with a motor running in a high PP02 environment. Not only is this an idea that has no value from any performance standpoint, it is frankly dangerous. Hyperbaric environments with high PP02 potentials are always a fireproof environment, lighting is a hyperbaric chamber is done with fiber optic tubes (no electrics in the chamber), heating is done with water heat exchangers, fans are run remotely thru magnetic drives, etc. NO MOTORS would ever be allowed... and a rebreather loop ought to be handled the same way. There is no problem to solve here, so why make one up?

Dive more. Dream less.

Dave

**Gill Envy** · 19th February 2007, 19:45

TC, while I can't speak to the value of your suggestion, I have wondered if creating such a thing to dry out the loop post dive wouldn't be the way to go. I've even looked at computer fans for the purpose and may someday get around to creating a hose fitting.
g

Quote: (Originally Posted by Lure_Angler)

Dear all,

It just occur to me:

What would happen if I place a ventilation fan (read: motherboard cooling fans), blowing in the direction of the gas flow in a rebreather's loop?

I reckon we'll probably get better WOB, better scrubbed air since the gas now moves thru the scrubber more times.

we could probably do away with the check valves too = better WOB?

Con: more electronics, one more point of failure. whirring sound from fan scares fish away?

comments pls, thank you.

TC

HooKeTePoo · 19th February 2007, 22:59

Quote: (Originally Posted by Gill Envy)

I have wondered if creating such a thing to dry out the loop post dive wouldn't be the way to go. I've even looked at computer fans for the purpose and may someday get around to creating a hose fitting.
g

I was thinking about this the other day g. I have been doing multiple dives back 2 back to recover a hard drive for a guy and my loop/lungs could have used some dryness bad! maybe just detach & plug scrubber insert fan adapter into p-port on lung (inhale side) I would just worry about deforming/stressing mushroom valves, shortening the life.. maybe add in a timer. That sort of thing would be great between dives and after cleaning/disinfecting the loop.
Are we just gadget crazy?

**Dave Sutton** · 20th February 2007, 00:11

Quote: (Originally Posted by HooKeTePoo)

I was thinking about this the other day g. I have been doing multiple dives back 2 back to recover a hard drive for a guy and my loop/lungs could have used some dryness bad! maybe just detach & plug scrubber insert fan adapter into p-port on lung (inhale side) I would just worry about deforming/stressing mushroom valves, shortening the life.. maybe add in a timer. That sort of thing would be great between dives and after cleaning/disinfecting the loop.
Are we just gadget crazy?

No, electric fan driers have been common for years for drying loops. I use a hair drier set to produce no heat, just air. The first Halcyon "refrigerators" used to come with a drying blower. Really, when diving day to day it's not an issue, just leave it damp. But preparing for storage is made easier, for sure.

The idea of running a fan inside a rebreather "not designed for saturation diving" while diving is, in my opinion, not sensible. And even in deep diving (IE 300 meters+) we did not find the need, however we did have an assisted breathing system "to an extent" with the push-pull system "vacuuming" exhaust gas back to the bell for scrubbing and then subsequently "pushing" the scrubbed gas back to the divers helmet.

In case anyone is interested, here is the system I worked on back in the late 70's and early 80's. The system was being evaluated by Santa Fe Engineering and Construction, my employer at the time. Divex and Santa Fe were "joined at the waist", we being the largest user of the Divex-3000 umbilical fed mixed gas rebreather.

Arawak System

It was a beautifully built thing. The pump pack sat on the outside of the SDC (Bell) and the helmet was a work of art.

Here's a shot of the hemet, courtesy of Divex:

Divex

I'd love to have one, the latching mechanism was like jewelry. When you pulled the bail down and it latched, it felt like you had closed the door of the space shuttle. Recirc hoses came down the front of the diver, and then to the backpack. Gorgeous stuff.

In any case, I am still not sure about fans for any submerged application.....

Dave

AD_ward9 · 20th February 2007, 01:36

Quote: (Originally Posted by Dave Sutton)

The idea of running a fan inside a rebreather "not designed for saturation diving" while diving is, in my opinion, not sensible.

On this we agree, well ... almost. Breathing assist is needed where the WOB is more than permitted in EN14143, after all other alternatives have been exhausted. The only time that happens is in extremely deep dives. I can see some technical diving applications for that, but overwhelmingly it is sat diving. The difference between extreme cave diving with deco habitats and sat diving starts to become blurred.

Quote: (Originally Posted by Dave Sutton)

And even in deep diving (IE 300 meters+) we did not find the need, however we did have an assisted breathing system "to an extent" with the push-pull system "vacuuming" exhaust gas back to the bell for scrubbing and then subsequently "pushing" the scrubbed gas back to the divers helmet.

Flow through was a nice idea, but the biggest obstruction and limit to the WOB is the diver's mouth. That is, the opening formed by the diver's teeth and jaw is smaller than any in rebreather designed for deep diving. The rest of the rebreather can manage 7 to 10sqcm of cross section easily, but the teeth are the problem. One needs something to bite on to get the jaw open, rather than the oro-nasal mask. This sort of diving favours really old guys ..

Thanks for raising the Arawak system. It was a very nice idea for the time and very well engineered. With many good ideas there is a tiny drawback, which grows and overwhelms it. For the RB211 turbo fan jet engine that sunk Rolls Royce in 1971, it was a frozen chicken: carbon fibre turbine blades do not like the US acceptance test of firing a chicken straight out of a deep freeze into them when running. For the Arawak, the big umbilical was its "frozen chicken". Pulling an umbilical for straight surface supply is hard enough, but with the hoses for the Arawak on it as well, was too much.

The Arawak provided flow through, like in a free flow helmet, rather than actual breathing assist, unless the diver chose to try and sync, in which case there would be a tiny bit of assist, and his work output would then also be synchronised, unfortunately.

The manned trials I referred to was not Arawak but a genuine breathing assist by a company in Norway 18 years ago. An area that has been rekindled, with divers starting to replace ROVs for some tasks and some of the extreme cave dives.

Alex

19th February 2007, 13:43	#1 (permalink)
Lure_Angler New Member Current Rebreather/s: Home Build Not Bought Yet Other Rebreather/s: Home Build Not Bought Yet Join Date: Nov 2006 Location: Singapore Posts: 68	Ventilation Fan in Loop Dear all, It just occur to me: What would happen if I place a ventilation fan (read: motherboard cooling fans), blowing in the direction of the gas flow in a rebreather's loop? I reckon we'll probably get better WOB, better scrubbed air since the gas now moves thru the scrubber more times. we could probably do away with the check valves too = better WOB? Con: more electronics, one more point of failure. whirring sound from fan scares fish away? comments pls, thank you. TC
(Offline)

19th February 2007, 14:39	#2 (permalink)
Sutty Classic Kiss diver Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Jun 2005 Location: Glossop, Derbyshire, UK Posts: 837	Re: Ventilation Fan in Loop Museums of old anaesthetic equipment include a "circle" system (i.e. loop with absorber etc, run semi-closed), which used the energy of gas injection to help circulate the gas around the loop. Long since abandoned, interesting as the WOB of current circle systems is awful (I tried breathing on one). Problems with your idea include: 1. Electric fan in a condensing atmosphere 2. Probably still need valves in case of failure 3. If fan fails will increase WOB compared to no fan 4. Might need to monitor gas flow in the loop to confirm operation However there could be some mileage in powered gas movement for very deep dives with high gas densities in the loop. Not sure I'd fancy testing it though! Neil __________________ Never forget that life is a finite resource.
(Offline)

19th February 2007, 14:45	#3 (permalink)
divetheworld Dive porn pimp Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Classic Kiss Other CCR Join Date: Mar 2005 Location: Leeds, England Posts: 1,636	Re: Ventilation Fan in Loop Quote: (Originally Posted by Lure_Angler) I reckon we'll probably get <snip> better scrubbed air since the gas now moves thru the scrubber more times. comments pls, thank you. TC Potential for the opposite. Think dwell time........ __________________ Attitude and self praise is no reccomendation. Dont try to be a great man, just be a man and let history be the judge of you. *WWW.NARKEDAT90.CO.UK* *http://www.grpservices.com/pursuit/* Supporting Shearwater Research Products in Europe Last edited by divetheworld : 19th February 2007 at 23:24.
(Offline)

19th February 2007, 14:51	#4 (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: Ventilation Fan in Loop Some tit bits that may help, from someone who has actually done this for a very deep rebreather: 1. Each blade of a fan, such as a computer fan, can develop around 4mbar of pressure differential across it, due to their low speed (they have a small diameter, so linear speeds compared to an aircraft propeller, is low and the area involved is small). The blades do work more efficiently at depth, increasing linearly with pressure in ATM, but 3 times less efficiently in helium. 2. You can increase the pressure by stacking blades like a turbine. If you are trying to reduce the WOB, then it is probably because the WOB is too high. This means you are probably going for a reduction in breathing resistance in excess of 25mbar (the EN14143:2003 breathing resistance limit). That requires 8 or so blades. An 8 blade compressor is noisy. 3. Fans contain PVC and volatile greases. 4. Doing this with optimal control causes the inhale counterlung to be always full, and the counterlung to be always empty when balanced, and when not, both counterlungs are full. 5. There are better ways to achieve reductions in WOB. You do not describe what your reasons are: is it a bad design of rebreather or that you want to dive where no man has gone before on SCUBA? Alex Quote: (Originally Posted by Lure_Angler) Dear all, It just occur to me: What would happen if I place a ventilation fan (read: motherboard cooling fans), blowing in the direction of the gas flow in a rebreather's loop? I reckon we'll probably get better WOB, better scrubbed air since the gas now moves thru the scrubber more times. we could probably do away with the check valves too = better WOB? Con: more electronics, one more point of failure. whirring sound from fan scares fish away? comments pls, thank you. TC Last edited by AD_ward9 : 19th February 2007 at 19:24.
(Offline)

19th February 2007, 19:18	#5 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Evolution Megalodon rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,907	Re: Ventilation Fan in Loop [quote=Lure_Angler;97324]whirring sound from fan scares fish away? /quote] No, just the odd diver who is afraid of being blown up in an 02 fire with a motor running in a high PP02 environment. Not only is this an idea that has no value from any performance standpoint, it is frankly dangerous. Hyperbaric environments with high PP02 potentials are always a fireproof environment, lighting is a hyperbaric chamber is done with fiber optic tubes (no electrics in the chamber), heating is done with water heat exchangers, fans are run remotely thru magnetic drives, etc. NO MOTORS would ever be allowed... and a rebreather loop ought to be handled the same way. There is no problem to solve here, so why make one up? Dive more. Dream less. Dave __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com Last edited by Dave Sutton : 19th February 2007 at 19:24.
(Offline)

19th February 2007, 19:27	#6 (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: Ventilation Fan in Loop Dave, I would differ on the issue of O2 compatibility here. A decent fan has a DC brushless direct drive motor. What is the reason for it not being in the loop? The windings are copper. Copper is a highly O2 compatible material. The blades of the fan are coated aluminium, as is the fan frame. For a PPO2 of only 1.3, that is fine. The iron armature may be nickel plated, but in any case is protected from the gas stream. Davy Lamp principle applies - only slight pun intended: Sir Humphry Davy invented it in 1816 and saved very many lives. The problem is the bearings: the grease has to be replaced, but that is fairly simple. The PVC has to be replaced: it is the wires from the windings. That is fairly simple again, replacing with Kynar covered multistrand plated wire. Where is the O2 hazard? I am not saying the fan is the way to do this, but the issue is not one of O2 compatibility, if properly executed. They are instead the practical issues: noise, size, power, control. It is also not a dream: Manned underwater rebreather dives to 450msw have been carried out in the sea with one of the breathing assistance systems that has been developed (not ours, alas, so far). It is a real issue for diving in places such as off of Brazil, where dives to 300m are carried out daily. Not many rebreathers work well at 300m. Or 600m. These are quite serious dives. There is a need for breathing assistance in rebreathers for this sort of stuff and at least three companies have units that do just that, or try to. I do not suggest for a moment, the divers on this thread had in mind such dives, but that is where breathing assistance has its application. Some caves dives could also benefit from these systems. Incidentally, if the fan/piston/bellows shift the same amount of air as your lungs, then the scrubber dwell time is not affected. This control is not trivial. Alex [quote=Dave Sutton;97394] Quote: (Originally Posted by Lure_Angler) whirring sound from fan scares fish away? /quote] No, just the odd diver who is afraid of being blown up in an 02 fire with a motor running in a high PP02 environment. Not only is this an idea that has no value from any performance standpoint, it is frankly dangerous. Hyperbaric environments with high PP02 potentials are always a fireproof environment, lighting is a hyperbaric chamber is done with fiber optic tubes (no electrics in the chamber), heating is done with water heat exchangers, fans are run remotely thru magnetic drives, etc. NO MOTORS would ever be allowed... and a rebreather loop ought to be handled the same way. There is no problem to solve here, so why make one up? Dive more. Dream less. Dave Last edited by AD_ward9 : 19th February 2007 at 20:07.
(Offline)

19th February 2007, 19:45	#7 (permalink)
Gill Envy Shearwater Copis Divers Current Rebreather/s: Other CCR Other Rebreather/s: Evolution Other CCR Join Date: Nov 2005 Location: seattle Posts: 1,347	Re: Ventilation Fan in Loop TC, while I can't speak to the value of your suggestion, I have wondered if creating such a thing to dry out the loop post dive wouldn't be the way to go. I've even looked at computer fans for the purpose and may someday get around to creating a hose fitting. g Quote: (Originally Posted by Lure_Angler) Dear all, It just occur to me: What would happen if I place a ventilation fan (read: motherboard cooling fans), blowing in the direction of the gas flow in a rebreather's loop? I reckon we'll probably get better WOB, better scrubbed air since the gas now moves thru the scrubber more times. we could probably do away with the check valves too = better WOB? Con: more electronics, one more point of failure. whirring sound from fan scares fish away? comments pls, thank you. TC __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°>
(Offline)

19th February 2007, 22:59	#8 (permalink)
HooKeTePoo New Member Current Rebreather/s: Dolphin Other Rebreather/s: Dolphin Join Date: Jun 2006 Location: Austin Tx Posts: 19	Re: Ventilation Fan in Loop Quote: (Originally Posted by Gill Envy) I have wondered if creating such a thing to dry out the loop post dive wouldn't be the way to go. I've even looked at computer fans for the purpose and may someday get around to creating a hose fitting. g I was thinking about this the other day g. I have been doing multiple dives back 2 back to recover a hard drive for a guy and my loop/lungs could have used some dryness bad! maybe just detach & plug scrubber insert fan adapter into p-port on lung (inhale side) I would just worry about deforming/stressing mushroom valves, shortening the life.. maybe add in a timer. That sort of thing would be great between dives and after cleaning/disinfecting the loop. Are we just gadget crazy?
(Offline)

20th February 2007, 00:11	#9 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Evolution Megalodon rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,907	Re: Ventilation Fan in Loop Quote: (Originally Posted by HooKeTePoo) I was thinking about this the other day g. I have been doing multiple dives back 2 back to recover a hard drive for a guy and my loop/lungs could have used some dryness bad! maybe just detach & plug scrubber insert fan adapter into p-port on lung (inhale side) I would just worry about deforming/stressing mushroom valves, shortening the life.. maybe add in a timer. That sort of thing would be great between dives and after cleaning/disinfecting the loop. Are we just gadget crazy? No, electric fan driers have been common for years for drying loops. I use a hair drier set to produce no heat, just air. The first Halcyon "refrigerators" used to come with a drying blower. Really, when diving day to day it's not an issue, just leave it damp. But preparing for storage is made easier, for sure. The idea of running a fan inside a rebreather "not designed for saturation diving" while diving is, in my opinion, not sensible. And even in deep diving (IE 300 meters+) we did not find the need, however we did have an assisted breathing system "to an extent" with the push-pull system "vacuuming" exhaust gas back to the bell for scrubbing and then subsequently "pushing" the scrubbed gas back to the divers helmet. In case anyone is interested, here is the system I worked on back in the late 70's and early 80's. The system was being evaluated by Santa Fe Engineering and Construction, my employer at the time. Divex and Santa Fe were "joined at the waist", we being the largest user of the Divex-3000 umbilical fed mixed gas rebreather. Arawak System It was a beautifully built thing. The pump pack sat on the outside of the SDC (Bell) and the helmet was a work of art. Here's a shot of the hemet, courtesy of Divex: Divex I'd love to have one, the latching mechanism was like jewelry. When you pulled the bail down and it latched, it felt like you had closed the door of the space shuttle. Recirc hoses came down the front of the diver, and then to the backpack. Gorgeous stuff. In any case, I am still not sure about fans for any submerged application..... Dave __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com Last edited by Dave Sutton : 20th February 2007 at 00:18.
(Offline)

20th February 2007, 01:36	#10 (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: Ventilation Fan in Loop Quote: (Originally Posted by Dave Sutton) The idea of running a fan inside a rebreather "not designed for saturation diving" while diving is, in my opinion, not sensible. On this we agree, well ... almost. Breathing assist is needed where the WOB is more than permitted in EN14143, after all other alternatives have been exhausted. The only time that happens is in extremely deep dives. I can see some technical diving applications for that, but overwhelmingly it is sat diving. The difference between extreme cave diving with deco habitats and sat diving starts to become blurred. Quote: (Originally Posted by Dave Sutton) And even in deep diving (IE 300 meters+) we did not find the need, however we did have an assisted breathing system "to an extent" with the push-pull system "vacuuming" exhaust gas back to the bell for scrubbing and then subsequently "pushing" the scrubbed gas back to the divers helmet. Flow through was a nice idea, but the biggest obstruction and limit to the WOB is the diver's mouth. That is, the opening formed by the diver's teeth and jaw is smaller than any in rebreather designed for deep diving. The rest of the rebreather can manage 7 to 10sqcm of cross section easily, but the teeth are the problem. One needs something to bite on to get the jaw open, rather than the oro-nasal mask. This sort of diving favours really old guys .. Thanks for raising the Arawak system. It was a very nice idea for the time and very well engineered. With many good ideas there is a tiny drawback, which grows and overwhelms it. For the RB211 turbo fan jet engine that sunk Rolls Royce in 1971, it was a frozen chicken: carbon fibre turbine blades do not like the US acceptance test of firing a chicken straight out of a deep freeze into them when running. For the Arawak, the big umbilical was its "frozen chicken". Pulling an umbilical for straight surface supply is hard enough, but with the hoses for the Arawak on it as well, was too much. The Arawak provided flow through, like in a free flow helmet, rather than actual breathing assist, unless the diver chose to try and sync, in which case there would be a tiny bit of assist, and his work output would then also be synchronised, unfortunately. The manned trials I referred to was not Arawak but a genuine breathing assist by a company in Norway 18 years ago. An area that has been rekindled, with divers starting to replace ROVs for some tasks and some of the extreme cave dives. Alex Last edited by AD_ward9 : 20th February 2007 at 03:04.
(Offline)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode