constant IP regs, piston vs diaphragm

Tom Rose · 19th February 2007, 13:15

Quote: (Originally Posted by Dave Sutton)

We do not care *at all* about flow, we care about MASS (IE: mass of 02 per minute which is contained in a smaller VOLUME of gas as ambient pressure increases). This has been described in great detail elsewhere.
Dave

Hi Dave,

Perhaps we should define terms as you did so well in regulators.

Gas Flow in Physics and the air measurement field is defined as

(((Pressure X Volume))/Temperature)/velocity

Repeated below for ease of viewing for some customers

Pressure x Volume
______________
Temperature

______________________________

Velocity

reported as
Standard Liters per minute
Standard Cubic Feet minute

Standard being at standard atmospheric temperature and pressure (sea level and about 20 degrees STP

Only now there are a number of so called standards..enough to drive you crazy....our best reference for our calculations would be bars and liters and try to ignore temperature.

Mass flow adds in the molecular weight of the medium flowing...

The real problem is when we confuse the volume flowed with the STP volume flowed....because of an incomplete understanding of the general gas laws

Its that damned additional pressure at depth thing that gets people.....
Or lack of pressure for you jet jockeys...

For more I send you to the web

Standard conditions for temperature and pressure - Wikipedia, the free encyclopedia

Regards
Tom

**fireman** · 19th February 2007, 15:23

To beat the horse:
Stay with the Kiss system--fixed reg/fixed orifice.
If you want deep deep capacity add another reg (non fixed ip) with manual add. You get redundancy, and no depth limit. Since there are more moles of gas in the loop the deeper you go, loosing the auto add shouldn't matter much.
I don't know much, but it seems like if this is an issue for you and you don't KNOW the answer you are looking for trouble. If your fixed reg IP is 10 bar then your system won't be cmf below 231ffw, and you won't be able to add any O2 below 297ffw, too deep to be scratching you head and wondering if your modifications/homebuild is going to work.

Ben Field · 19th February 2007, 15:42

Okay maybe I introduced this in the wrong thread, we're missing the point by a considerable margin here.

To reiterate- I'm not modifying/changing/playing with anything nor do I want to.

I was simply asking a couple of questions to see if in fact the needle valve and additional O2 source people are going completly OTT to what might actually be a simply fix (theoretically anyway.)

Despite apperances I do know roughly what I'm talking about, I think I need a graph to explain it but don't have the software here to draw one...

I'll shut up for now and find a better way of explaining myself- thanks for the input/thoughts though everyone, very helpful

BEN

**Dave Sutton** · 19th February 2007, 15:47

Ben,

Put into words so simple a stupid test pilot can understand it exactly what your question is so we can hash it out. Describe exactly what sort of supply regulator you envision, what sort of needle valve, and then we can discuss.

Best,

Dave

dive2dive2000 · 19th February 2007, 15:50

Very interesting thread. I dive a PRISM and replaced my 1 stage pistons with Zeagle flat-head 6. I am confused about the plugging of the diaphragm. Is this recommended for ECCR or just MCCR? Could someone elaborate a little more. Thanks in advance

Tom Rose · 19th February 2007, 16:00

Quote: (Originally Posted by dive2dive2000)

Very interesting thread. I dive a PRISM and replaced my 1 stage pistons with Zeagle flat-head 6. I am confused about the plugging of the diaphragm. Is this recommended for ECCR or just MCCR? Could someone elaborate a little more. Thanks in advance

Your prism does not need to have a fixed ip.......leave it alone...you did move the over pressure relief valve to the new regulator....didn't you.

Tom Rose

dive2dive2000 · 19th February 2007, 16:14

Quote: (Originally Posted by Tom Rose)

Your prism does not need to have a fixed ip.......leave it alone...you did move the over pressure relief valve to the new regulator....didn't you.

Tom Rose

Yup one on the O2 and one on the dil. I don't use the scubapro inflator/reg so needed to add one on the dil. Thanks for reply

Shas · 19th February 2007, 22:33

Pete would like to add a couple of things to the discussion -

1. The equations for sonic flow or "Choked flow conditions" can be found at http://en.wikipedia.org/wiki/Choked_flow I used similar derivatives to calculate the flow for the Prism from the restrictor to the solenoid valve. The nominal interstage pressure is designed to be between 121 to 140 psi which meant we could use a low wattage solenoid.
An excellent reference book which you may find helpful "Life Support Systems Design" by Nuckols, Tucker and Sarich. This goes into a little more detail with regards to gas flow for UBA's, I now use CFD programs Cosmos and NIKA.

2. Marty - Please note that the ScubaPro Mk2's were chosen for the PRISM because they are simple to maintain, have a single moving part and after testing are very oxygen tolerant and reliable. It was an important consideration to include oxygen compatibility of materials and flow design into our choice. The regulators, restrictor, solenoid and associated pipe work are designed to be part of a system. Changing any of these may upset the hysterias of the system for accurate PO2 control, not to mention increase the risk of adiabatic compression problems (fire) or solenoid failure with higher interstage pressures.

dive2dive2000 · 20th February 2007, 00:00

Quote: (Originally Posted by Shas)

Pete would like to add a couple of things to the discussion -

1. The equations for sonic flow or "Choked flow conditions" can be found at http://en.wikipedia.org/wiki/Choked_flow I used similar derivatives to calculate the flow for the Prism from the restrictor to the solenoid valve. The nominal interstage pressure is designed to be between 121 to 140 psi which meant we could use a low wattage solenoid.
An excellent reference book which you may find helpful "Life Support Systems Design" by Nuckols, Tucker and Sarich. This goes into a little more detail with regards to gas flow for UBA's, I now use CFD programs Cosmos and NIKA.

2. Marty - Please note that the ScubaPro Mk2's were chosen for the PRISM because they are simple to maintain, have a single moving part and after testing are very oxygen tolerant and reliable. It was an important consideration to include oxygen compatibility of materials and flow design into our choice. The regulators, restrictor, solenoid and associated pipe work are designed to be part of a system. Changing any of these may upset the hysterias of the system for accurate PO2 control, not to mention increase the risk of adiabatic compression problems (fire) or solenoid failure with higher interstage pressures.

Hi guys

Nice to see you lurking about RBW. The only reason I switched 1st stages I can service Zeagles, it is a pita to services scubapro's all of the LDS that are scubapro dealers I don't do business with. I have adjusted my IP accordingly and have not had any issues. Hope to see you at BTS

**Dave Sutton** · 20th February 2007, 00:22

Quote: (Originally Posted by Shas)

Changing any of these may upset the hysterias of the system for accurate PO2 control

Changing the *brand of the supply regulator* has a potential to upset the P02 control? Really. Do please tell us why.
I must have missed that part of my fluid dynamics class and would love to have my engineering deficiencies corrected.

(x) PSI suppled at (y) LPM is all that is required to serve the downstream system.

Can the physics of the equation read a brand name on the regulator?

Color me skeptical of "special design" claims (as usual).....

Dave Sutton

19th February 2007, 13:15	#31 (permalink)
Tom Rose Still Learning Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Prism Topaz Other CCR Home Build Join Date: Oct 2005 Location: USA,North Carolina Posts: 331	Re: constant IP regs, piston vs diaphragm Quote: (Originally Posted by Dave Sutton) We do not care at all about flow, we care about MASS (IE: mass of 02 per minute which is contained in a smaller VOLUME of gas as ambient pressure increases). This has been described in great detail elsewhere. Dave Hi Dave, Perhaps we should define terms as you did so well in regulators. Gas Flow in Physics and the air measurement field is defined as (((Pressure X Volume))/Temperature)/velocity Repeated below for ease of viewing for some customers Pressure x Volume ______________ Temperature ______________________________ Velocity reported as Standard Liters per minute Standard Cubic Feet minute Standard being at standard atmospheric temperature and pressure (sea level and about 20 degrees STP Only now there are a number of so called standards..enough to drive you crazy....our best reference for our calculations would be bars and liters and try to ignore temperature. Mass flow adds in the molecular weight of the medium flowing... The real problem is when we confuse the volume flowed with the STP volume flowed....because of an incomplete understanding of the general gas laws Its that damned additional pressure at depth thing that gets people..... Or lack of pressure for you jet jockeys... For more I send you to the web Standard conditions for temperature and pressure - Wikipedia, the free encyclopedia Regards Tom __________________ The 50-50-90 rule: Anytime I have a 50-50 chance of getting something right, there's a 90% probability I'll get it wrong the first time. www.atlimp.com Last edited by Tom Rose : 19th February 2007 at 13:29. Reason: Added references to stp and link
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19th February 2007, 15:23	#32 (permalink)
fireman rEvo combat swimmer Current Rebreather/s: rEvo Other CCR Other Rebreather/s: rEvo Other CCR Join Date: Nov 2006 Location: chicago Posts: 550	Re: constant IP regs, piston vs diaphragm To beat the horse: Stay with the Kiss system--fixed reg/fixed orifice. If you want deep deep capacity add another reg (non fixed ip) with manual add. You get redundancy, and no depth limit. Since there are more moles of gas in the loop the deeper you go, loosing the auto add shouldn't matter much. I don't know much, but it seems like if this is an issue for you and you don't KNOW the answer you are looking for trouble. If your fixed reg IP is 10 bar then your system won't be cmf below 231ffw, and you won't be able to add any O2 below 297ffw, too deep to be scratching you head and wondering if your modifications/homebuild is going to work. __________________ Heres to you Capt. Bill Never Forget, and stay safe everyone.
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19th February 2007, 15:42	#33 (permalink)
Ben Field CK+Shearwater Current Rebreather/s: Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Aug 2005 Location: London, England Posts: 1,780	Re: constant IP regs, piston vs diaphragm Okay maybe I introduced this in the wrong thread, we're missing the point by a considerable margin here. To reiterate- I'm not modifying/changing/playing with anything nor do I want to. I was simply asking a couple of questions to see if in fact the needle valve and additional O2 source people are going completly OTT to what might actually be a simply fix (theoretically anyway.) Despite apperances I do know roughly what I'm talking about, I think I need a graph to explain it but don't have the software here to draw one... I'll shut up for now and find a better way of explaining myself- thanks for the input/thoughts though everyone, very helpful BEN __________________ Know your PPO2, Pre-breath, Use checklists, Validate cells at 6mtrs, Use pure O2 at or near surface, Use a BOV, Don't dive Solo, Change Slime and Cells as recommended by Manufacturer and RTFM! www.hugsac.org.uk
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19th February 2007, 15:47	#34 (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: 2,913	Re: constant IP regs, piston vs diaphragm Ben, Put into words so simple a stupid test pilot can understand it exactly what your question is so we can hash it out. Describe exactly what sort of supply regulator you envision, what sort of needle valve, and then we can discuss. Best, Dave __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com
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19th February 2007, 15:50	#35 (permalink)
dive2dive2000 PRISM DIVER & LUVIN IT! Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Feb 2005 Location: Long Island, NY Posts: 796	Re: constant IP regs, piston vs diaphragm Very interesting thread. I dive a PRISM and replaced my 1 stage pistons with Zeagle flat-head 6. I am confused about the plugging of the diaphragm. Is this recommended for ECCR or just MCCR? Could someone elaborate a little more. Thanks in advance __________________ Safe Diving, Martin
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19th February 2007, 16:00	#36 (permalink)
Tom Rose Still Learning Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Prism Topaz Other CCR Home Build Join Date: Oct 2005 Location: USA,North Carolina Posts: 331	Re: constant IP regs, piston vs diaphragm Quote: (Originally Posted by dive2dive2000) Very interesting thread. I dive a PRISM and replaced my 1 stage pistons with Zeagle flat-head 6. I am confused about the plugging of the diaphragm. Is this recommended for ECCR or just MCCR? Could someone elaborate a little more. Thanks in advance Your prism does not need to have a fixed ip.......leave it alone...you did move the over pressure relief valve to the new regulator....didn't you. Tom Rose __________________ The 50-50-90 rule: Anytime I have a 50-50 chance of getting something right, there's a 90% probability I'll get it wrong the first time. www.atlimp.com
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19th February 2007, 16:14	#37 (permalink)
dive2dive2000 PRISM DIVER & LUVIN IT! Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Feb 2005 Location: Long Island, NY Posts: 796	Re: constant IP regs, piston vs diaphragm Quote: (Originally Posted by Tom Rose) Your prism does not need to have a fixed ip.......leave it alone...you did move the over pressure relief valve to the new regulator....didn't you. Tom Rose Yup one on the O2 and one on the dil. I don't use the scubapro inflator/reg so needed to add one on the dil. Thanks for reply __________________ Safe Diving, Martin
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19th February 2007, 22:33	#38 (permalink)
Shas New Member Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Mar 2005 Location: Lebanon, TN Posts: 11	Re: constant IP regs, piston vs diaphragm Pete would like to add a couple of things to the discussion - 1. The equations for sonic flow or "Choked flow conditions" can be found at http://en.wikipedia.org/wiki/Choked_flow I used similar derivatives to calculate the flow for the Prism from the restrictor to the solenoid valve. The nominal interstage pressure is designed to be between 121 to 140 psi which meant we could use a low wattage solenoid. An excellent reference book which you may find helpful "Life Support Systems Design" by Nuckols, Tucker and Sarich. This goes into a little more detail with regards to gas flow for UBA's, I now use CFD programs Cosmos and NIKA. 2. Marty - Please note that the ScubaPro Mk2's were chosen for the PRISM because they are simple to maintain, have a single moving part and after testing are very oxygen tolerant and reliable. It was an important consideration to include oxygen compatibility of materials and flow design into our choice. The regulators, restrictor, solenoid and associated pipe work are designed to be part of a system. Changing any of these may upset the hysterias of the system for accurate PO2 control, not to mention increase the risk of adiabatic compression problems (fire) or solenoid failure with higher interstage pressures.
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20th February 2007, 00:00	#39 (permalink)
dive2dive2000 PRISM DIVER & LUVIN IT! Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Feb 2005 Location: Long Island, NY Posts: 796	Re: constant IP regs, piston vs diaphragm Quote: (Originally Posted by Shas) Pete would like to add a couple of things to the discussion - 1. The equations for sonic flow or "Choked flow conditions" can be found at http://en.wikipedia.org/wiki/Choked_flow I used similar derivatives to calculate the flow for the Prism from the restrictor to the solenoid valve. The nominal interstage pressure is designed to be between 121 to 140 psi which meant we could use a low wattage solenoid. An excellent reference book which you may find helpful "Life Support Systems Design" by Nuckols, Tucker and Sarich. This goes into a little more detail with regards to gas flow for UBA's, I now use CFD programs Cosmos and NIKA. 2. Marty - Please note that the ScubaPro Mk2's were chosen for the PRISM because they are simple to maintain, have a single moving part and after testing are very oxygen tolerant and reliable. It was an important consideration to include oxygen compatibility of materials and flow design into our choice. The regulators, restrictor, solenoid and associated pipe work are designed to be part of a system. Changing any of these may upset the hysterias of the system for accurate PO2 control, not to mention increase the risk of adiabatic compression problems (fire) or solenoid failure with higher interstage pressures. Hi guys Nice to see you lurking about RBW. The only reason I switched 1st stages I can service Zeagles, it is a pita to services scubapro's all of the LDS that are scubapro dealers I don't do business with. I have adjusted my IP accordingly and have not had any issues. Hope to see you at BTS __________________ Safe Diving, Martin
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20th February 2007, 00:22	#40 (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: 2,913	Re: constant IP regs, piston vs diaphragm Quote: (Originally Posted by Shas) Changing any of these may upset the hysterias of the system for accurate PO2 control Changing the brand of the supply regulator has a potential to upset the P02 control? Really. Do please tell us why. I must have missed that part of my fluid dynamics class and would love to have my engineering deficiencies corrected. (x) PSI suppled at (y) LPM is all that is required to serve the downstream system. Can the physics of the equation read a brand name on the regulator? Color me skeptical of "special design" claims (as usual)..... Dave Sutton __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com Last edited by Dave Sutton : 20th February 2007 at 00:39.
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