Expedition-level Mk 15.x MCCR in 90 seconds!

Philippe GERIN · 3rd July 2007, 14:50

Did you keep the accumulator for a specific reason or did you just leave it there because it's part of the "standard" rig (if any of our rig can be named that way)? Do you think it could act as a buffer so that the downstream pressure is less variable? Did you try without it ?
Best
Philippe

jeff h · 3rd July 2007, 15:42

I noticed the stated flow rates are for Helium flow at 50 psig. What IP are you using with the 0.75 liter valve and what output of O2 are you getting?

Thanks,

-Jeff

**Dave Sutton** · 3rd July 2007, 16:31

Quote: (Originally Posted by caveseeker7)

Don't I remember a recent 5 page thread regarding needle valves ...

And to do that to a MK ...

All agreed. It'll only have value above a needle valve if it acts as advertised.

Needle valves are not "bad" per-se. What I do not see as having value is the idea of adjusting them "on the fly". One buried inside the chassis is really just a pre-dive adjustable orifice. I don't see the value to one if you are using a diaphragm regulator that can be key-adjusted for IP, as that sets the flow. I *do* see them as value on a piston first stage system that cannot be dialed-in for IP to set flow, so *if* you wanted to bury one inside a Mark-15 that's not a bad design.

What works, works. Having an easy to swap-in orifice system for a Mark-15 sitting in your kit to save a trip after a pod fails is nice. Yes, you could just fly manually, but if you can take 10 minutes to remove the solenoid, add an orifice (no matter what sort) and then to revert to a KISS type system monitored on the secondary? Why not. For the guys who have old analog REV-G pods with bad transistors to the solenoid (IE: the primary and secondary work, but the solenoid is not fired) this would be a neat way to keep the rig going without changing the pod.

Best,

Dave

teksimple · 3rd July 2007, 16:31

Quote: (Originally Posted by Philippe GERIN)

Did you keep the accumulator for a specific reason or did you just leave it there because it's part of the "standard" rig (if any of our rig can be named that way)? Do you think it could act as a buffer so that the downstream pressure is less variable? Did you try without it ?
Best
Philippe

I wondered if the accumulator would cause issues, but since it worked just fine with it on, I never tried it with it off. I like the fact that I can switch back and forth in just minutes, changing only what was needed.

teksimple · 3rd July 2007, 16:43

Quote: (Originally Posted by jeff h)

I noticed the stated flow rates are for Helium flow at 50 psig. What IP are you using with the 0.75 liter valve and what output of O2 are you getting?

Thanks,

-Jeff

Yes, the Porter valve was originally designed to be used for the carrier gas (helium) of a gas chromatograh, so the flow element number will be considerably different for a gas with different R and viscosity values (like oxygen). The guys at Porter Instruments are familiar with it. The knob on my unit using the 400 laminar flow element has been turned down to about 0.25 liters /minute from the approximate 170psi/11.7 bar intermediate pressure.

**Gill Envy** · 3rd July 2007, 16:55

Thanks Simon, have some green! that helped a lot. What a cool device...i'll probably never have a need for one, but soo cool to see it getting "discovered" and understanding it's value in an mCCR application for getting around the IP depth limitation issue. Like so many other little widgets, maybe it's price will come down if it gets mass produced...interested in seeing if it eventually becomes the tool for even shallow mCCR diving. it's kind of a nice inbetween of a needle valve and a CFO...adjustible but stable enough to leave alone during a dive to pretty much any depth...

my little axe to grind: this may make the solenoid irrelevant for many, if not all applications. Certainly the average set point controller adds more than $800 to the cost of a rebreather.

In any case, being able to switch back and forth between eCCR and mCCR will make managing equipment failure without lossing dive time a lot more feasable for eCCR divers.

g

Quote: (Originally Posted by SimonK)

OK an attempt to explain it in plain english and a wonderful oppertunity to make an ass of myself by getting it wrong.

The gas flows through a set of very small tubes which enforce laminar flow. The flow rate is proportional to the pressure differential across the tubes. The clever bit about laminar flow is that as the absolute pressure increases so does the gas density, and as a result the viscosity. The increase in viscosity results in reduced volumetric flow to maintain the same pressure differential. So if we maintain the pressure differential as the ambient pressure goes up the volumetric flow reduces and the mass flow (volume x density) stays constant.

Laminar flow: turn a tap on until you get a smooth flow of water, thats laminar flow. Turn the tap on further and the water flow becomes chaotic - thats turbulent flow.

Simon

teksimple · 3rd July 2007, 17:04

To accommodate the number of PM requests for the Swagelok parts I used, here they are:

SS-300-6-2 1/8" to 3/16" reducing union (2)
SS-200-SET 1/8" ferrule set (not needed if you are a pipe forming genius and do not need to redo a section like I had to)
1/8" OD stainless tubing (as needed)

I should not have to explain that you need to carefully cut and debur, as well as clean (boiling water and TSP/soap) all tubing and parts to be used for oxygen service.

SimonK · 3rd July 2007, 22:02

Quote: (Originally Posted by Gill Envy)

Thanks Simon, have some green! that helped a lot. What a cool device...i'll probably never have a need for one, but soo cool to see it getting "discovered" and understanding it's value in an mCCR application for getting around the IP depth limitation issue. Like so many other little widgets, maybe it's price will come down if it gets mass produced...interested in seeing if it eventually becomes the tool for even shallow mCCR diving. it's kind of a nice inbetween of a needle valve and a CFO...adjustible but stable enough to leave alone during a dive to pretty much any depth...

my little axe to grind: this may make the solenoid irrelevant for many, if not all applications. Certainly the average set point controller adds more than $800 to the cost of a rebreather.

In any case, being able to switch back and forth between eCCR and mCCR will make managing equipment failure without lossing dive time a lot more feasable for eCCR divers.

g

Gill

having done a bit more reading it looks like my explanation isn't quite right. The viscosity of oxygen only changes by about 10% over a 30 Bar range. Something else must be going on to get a constant mass flow, more reading required!

Simon

**Gill Envy** · 3rd July 2007, 22:38

Quote: (Originally Posted by SimonK)

Gill

having done a bit more reading it looks like my explanation isn't quite right. The viscosity of oxygen only changes by about 10% over a 30 Bar range. Something else must be going on to get a constant mass flow, more reading required!

Simon

thanks for the correction Simon. hope the explanation you find is something I can wrap my mind around as well as your previous one.
g

hrdubwd · 4th July 2007, 01:45

Quote: (Originally Posted by SimonK)

The gas flows through a set of very small tubes which enforce laminar flow. The flow rate is proportional to the pressure differential across the tubes. The clever bit about laminar flow is that as the absolute pressure increases so does the gas density, and as a result the viscosity. The increase in viscosity results in reduced volumetric flow to maintain the same pressure differential. So if we maintain the pressure differential as the ambient pressure goes up the volumetric flow reduces and the mass flow (volume x density) stays constant.

There is something wrong here. All the sources say something to this effect:
"The impact of pressure is minor, and the viscosity correction for pressure is less than 10% for [these] gases for pressures up to 34.5 bar."

For example:
from Barrow, Physical Chemistry, 4th ed, p 49 (McGraw-Hill)
"The theoretical derivation therefore makes the prediction that the viscosity of a gas should be independent of the pressure and proportional to the square root of the absolute temperature. This rather remarkable result (it seems "reasonable" that the viscosity of a gas should increase as the gas is compressed and becomes more dense) was one of the few theoretical deductions to be made before the experimental measurements had been performed. Maxwell's prediction of this behaviour and its subsequent experimental verification provided one of the most dramatic triumphs of the kinetic molecular theory."

On this basis, I can only conclude that *if * mass flow rate is constant for this device there is something else going on. It is not as simple as it seems, and it is unlikely to be an 'auto-compensation' based on density for laminar flow. If the rotameter trial data is recalculated to get mass flow it would help, but I think we need to be a bit cautious at the moment. The "clever bit" seems not to be true.

BWD

3rd July 2007, 14:50	#41 (permalink)
Philippe GERIN ccr apprentice Current Rebreather/s: Megalodon Classic Kiss Other Rebreather/s: Join Date: May 2005 Location: Strasbourg, France Posts: 636	Re: Expedition-level Mk 15.x MCCR in 90 seconds! Did you keep the accumulator for a specific reason or did you just leave it there because it's part of the "standard" rig (if any of our rig can be named that way)? Do you think it could act as a buffer so that the downstream pressure is less variable? Did you try without it ? Best Philippe
(Online)

3rd July 2007, 15:42	#42 (permalink)
jeff h New Member Current Rebreather/s: Megalodon Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Feb 2006 Location: Michigan Posts: 97	Re: Expedition-level Mk 15.x MCCR in 90 seconds! I noticed the stated flow rates are for Helium flow at 50 psig. What IP are you using with the 0.75 liter valve and what output of O2 are you getting? Thanks, -Jeff
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3rd July 2007, 16:31	#43 (permalink)
Dave Sutton Diveshop of Horrors Current Rebreather/s: Sport Kiss MK 15.X rEvo Other CCR Azimuth Home Build Other Rebreather/s: Classic Kiss rEvo Other CCR Azimuth Home Build Join Date: Jun 2006 Location: Narragansett, Rhode Island and Hackettstown, New Jersey Posts: 2,672	Re: MK15.... with ... a NEEDLE VALVE ! Quote: (Originally Posted by caveseeker7) Don't I remember a recent 5 page thread regarding needle valves ... And to do that to a MK ... All agreed. It'll only have value above a needle valve if it acts as advertised. Needle valves are not "bad" per-se. What I do not see as having value is the idea of adjusting them "on the fly". One buried inside the chassis is really just a pre-dive adjustable orifice. I don't see the value to one if you are using a diaphragm regulator that can be key-adjusted for IP, as that sets the flow. I do see them as value on a piston first stage system that cannot be dialed-in for IP to set flow, so if you wanted to bury one inside a Mark-15 that's not a bad design. What works, works. Having an easy to swap-in orifice system for a Mark-15 sitting in your kit to save a trip after a pod fails is nice. Yes, you could just fly manually, but if you can take 10 minutes to remove the solenoid, add an orifice (no matter what sort) and then to revert to a KISS type system monitored on the secondary? Why not. For the guys who have old analog REV-G pods with bad transistors to the solenoid (IE: the primary and secondary work, but the solenoid is not fired) this would be a neat way to keep the rig going without changing the pod. Best, Dave __________________ "Changes in Lattitudes, Changes in Attitudes, Nothing remains quite the same".... www.nobubblediving.com Last edited by Dave Sutton : 3rd July 2007 at 16:34.
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3rd July 2007, 16:31	#44 (permalink)
teksimple Enlightened Alpinist Current Rebreather/s: MK 15.X Other Rebreather/s: Sport Kiss Classic Kiss Join Date: Apr 2005 Location: Back in Hawaii Posts: 503	Re: Expedition-level Mk 15.x MCCR in 90 seconds! Quote: (Originally Posted by Philippe GERIN) Did you keep the accumulator for a specific reason or did you just leave it there because it's part of the "standard" rig (if any of our rig can be named that way)? Do you think it could act as a buffer so that the downstream pressure is less variable? Did you try without it ? Best Philippe I wondered if the accumulator would cause issues, but since it worked just fine with it on, I never tried it with it off. I like the fact that I can switch back and forth in just minutes, changing only what was needed. __________________ ---- _____________ "I don't know the percentage of the Internet that's valid, do you? Jesus, it's scary." - Hunter S. Thompson
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3rd July 2007, 16:43	#45 (permalink)
teksimple Enlightened Alpinist Current Rebreather/s: MK 15.X Other Rebreather/s: Sport Kiss Classic Kiss Join Date: Apr 2005 Location: Back in Hawaii Posts: 503	Re: Expedition-level Mk 15.x MCCR in 90 seconds! Quote: (Originally Posted by jeff h) I noticed the stated flow rates are for Helium flow at 50 psig. What IP are you using with the 0.75 liter valve and what output of O2 are you getting? Thanks, -Jeff Yes, the Porter valve was originally designed to be used for the carrier gas (helium) of a gas chromatograh, so the flow element number will be considerably different for a gas with different R and viscosity values (like oxygen). The guys at Porter Instruments are familiar with it. The knob on my unit using the 400 laminar flow element has been turned down to about 0.25 liters /minute from the approximate 170psi/11.7 bar intermediate pressure. __________________ ---- _____________ "I don't know the percentage of the Internet that's valid, do you? Jesus, it's scary." - Hunter S. Thompson
(Offline)

3rd July 2007, 16:55	#46 (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: Expedition-level Mk 15.x MCCR in 90 seconds! Thanks Simon, have some green! that helped a lot. What a cool device...i'll probably never have a need for one, but soo cool to see it getting "discovered" and understanding it's value in an mCCR application for getting around the IP depth limitation issue. Like so many other little widgets, maybe it's price will come down if it gets mass produced...interested in seeing if it eventually becomes the tool for even shallow mCCR diving. it's kind of a nice inbetween of a needle valve and a CFO...adjustible but stable enough to leave alone during a dive to pretty much any depth... my little axe to grind: this may make the solenoid irrelevant for many, if not all applications. Certainly the average set point controller adds more than $800 to the cost of a rebreather. In any case, being able to switch back and forth between eCCR and mCCR will make managing equipment failure without lossing dive time a lot more feasable for eCCR divers. g Quote: (Originally Posted by SimonK) OK an attempt to explain it in plain english and a wonderful oppertunity to make an ass of myself by getting it wrong. The gas flows through a set of very small tubes which enforce laminar flow. The flow rate is proportional to the pressure differential across the tubes. The clever bit about laminar flow is that as the absolute pressure increases so does the gas density, and as a result the viscosity. The increase in viscosity results in reduced volumetric flow to maintain the same pressure differential. So if we maintain the pressure differential as the ambient pressure goes up the volumetric flow reduces and the mass flow (volume x density) stays constant. Laminar flow: turn a tap on until you get a smooth flow of water, thats laminar flow. Turn the tap on further and the water flow becomes chaotic - thats turbulent flow. Simon __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°> Last edited by Gill Envy : 3rd July 2007 at 16:57.
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3rd July 2007, 17:04	#47 (permalink)
teksimple Enlightened Alpinist Current Rebreather/s: MK 15.X Other Rebreather/s: Sport Kiss Classic Kiss Join Date: Apr 2005 Location: Back in Hawaii Posts: 503	Re: Expedition-level Mk 15.x MCCR in 90 seconds! To accommodate the number of PM requests for the Swagelok parts I used, here they are: SS-300-6-2 1/8" to 3/16" reducing union (2) SS-200-SET 1/8" ferrule set (not needed if you are a pipe forming genius and do not need to redo a section like I had to) 1/8" OD stainless tubing (as needed) I should not have to explain that you need to carefully cut and debur, as well as clean (boiling water and TSP/soap) all tubing and parts to be used for oxygen service. __________________ ---- _____________ "I don't know the percentage of the Internet that's valid, do you? Jesus, it's scary." - Hunter S. Thompson
(Offline)

3rd July 2007, 22:02	#48 (permalink)
SimonK Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Oct 2005 Location: Cumbria UK Posts: 231	Re: Expedition-level Mk 15.x MCCR in 90 seconds! Quote: (Originally Posted by Gill Envy) Thanks Simon, have some green! that helped a lot. What a cool device...i'll probably never have a need for one, but soo cool to see it getting "discovered" and understanding it's value in an mCCR application for getting around the IP depth limitation issue. Like so many other little widgets, maybe it's price will come down if it gets mass produced...interested in seeing if it eventually becomes the tool for even shallow mCCR diving. it's kind of a nice inbetween of a needle valve and a CFO...adjustible but stable enough to leave alone during a dive to pretty much any depth... my little axe to grind: this may make the solenoid irrelevant for many, if not all applications. Certainly the average set point controller adds more than $800 to the cost of a rebreather. In any case, being able to switch back and forth between eCCR and mCCR will make managing equipment failure without lossing dive time a lot more feasable for eCCR divers. g Gill having done a bit more reading it looks like my explanation isn't quite right. The viscosity of oxygen only changes by about 10% over a 30 Bar range. Something else must be going on to get a constant mass flow, more reading required! Simon
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3rd July 2007, 22:38	#49 (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: Expedition-level Mk 15.x MCCR in 90 seconds! Quote: (Originally Posted by SimonK) Gill having done a bit more reading it looks like my explanation isn't quite right. The viscosity of oxygen only changes by about 10% over a 30 Bar range. Something else must be going on to get a constant mass flow, more reading required! Simon thanks for the correction Simon. hope the explanation you find is something I can wrap my mind around as well as your previous one. g __________________ Gill Envy ...Because I wasn't born with gills! ><(°>><(°>><(°>><(°>><(°>><(°>><(°>><(°>
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4th July 2007, 01:45	#50 (permalink)
hrdubwd New Member Current Rebreather/s: Classic Kiss Other Rebreather/s: Join Date: Nov 2005 Posts: 86	Re: Expedition-level Mk 15.x MCCR in 90 seconds! Quote: (Originally Posted by SimonK) The gas flows through a set of very small tubes which enforce laminar flow. The flow rate is proportional to the pressure differential across the tubes. The clever bit about laminar flow is that as the absolute pressure increases so does the gas density, and as a result the viscosity. The increase in viscosity results in reduced volumetric flow to maintain the same pressure differential. So if we maintain the pressure differential as the ambient pressure goes up the volumetric flow reduces and the mass flow (volume x density) stays constant. There is something wrong here. All the sources say something to this effect: "The impact of pressure is minor, and the viscosity correction for pressure is less than 10% for [these] gases for pressures up to 34.5 bar." For example: from Barrow, Physical Chemistry, 4th ed, p 49 (McGraw-Hill) "The theoretical derivation therefore makes the prediction that the viscosity of a gas should be independent of the pressure and proportional to the square root of the absolute temperature. This rather remarkable result (it seems "reasonable" that the viscosity of a gas should increase as the gas is compressed and becomes more dense) was one of the few theoretical deductions to be made before the experimental measurements had been performed. Maxwell's prediction of this behaviour and its subsequent experimental verification provided one of the most dramatic triumphs of the kinetic molecular theory." On this basis, I can only conclude that if mass flow rate is constant for this device there is something else going on. It is not as simple as it seems, and it is unlikely to be an 'auto-compensation' based on density for laminar flow. If the rotameter trial data is recalculated to get mass flow it would help, but I think we need to be a bit cautious at the moment. The "clever bit" seems not to be true. BWD
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