constant IP regs, piston vs diaphragm

**jmurba** · 18th February 2007, 08:07

Quote: (Originally Posted by wedivebc)

If you are using an adjustable needle valve why do you even need constant IP?

Not to have to tune the flow rate on the fly of course
I use to do this with a swagelock needle valve it was great,
the valve was in the dolphin shell
but the hyrogom valve is better cause the 2 O2 addition modes are in only one set (constant and demand).

regards

jean mi

**jmurba** · 18th February 2007, 08:26

Quote: (Originally Posted by wedivebc)

Which is the whole point of using an adjustable needle valve. Orifice type leaky valve rebreathers are depth limited by the constant IP, adjustable needle valves aren't. Why use a needle valve then don't take advantage of that feature?

do you dive this way ?
in my opinion tunning the flow rate underwater is a difficult task ins't it ?

regards

jean mi

**Dave Sutton** · 18th February 2007, 12:39

Quote: (Originally Posted by OceanOpportunity)

in the case of needle valves, are these being referred to as a device that also restricts flow within a certain range, or a means to control the full spectrum from 'on' to 'off' with the IP flow from the LP hose? In other words, is the needle valve being used in conjunction with an orifice that say offers a max flow of 1lpm or thereabouts on the high end, so it can be tuned down during the dive to adjust for the IP increase on descent?

Not really...... these systems should never need to be managed during the dive. If you need to manage the system, it's no longer "simple", stupid!

There are two schools of thought:

(1): Fixed orifice, pick a size, and then adjust the first stage supply pressure to obtain the feed you desire.

(2): Adjustable orifice (needle valve): Set "some" regulator supply pressure and then adjust the *valve* to obtain the desired flow.

The *fallacy* is the idea that the needle valve ought to be managed during the dive. Those guys who "get it" use the needle valve during setup and then forget it. Those guys who "don't get it" are fiddling with the valve underwater. The problem is that the PP02 change rate response time is not short enough for the diver to be able to use feedback to adjust the valve in anywhere near real-time.

I am, personally, firmly in the case (1) mindset. I simply leave the orifice alone and use a hex key to adjust the flow. And since I do that about once a year, it does not seem to me to be worthwhile to have a far more comlex (and expensive) needle valve that I *never need to adjust*. The orifice I use costs me about $10.00. All diaphram regulators adjust with a key. I have all I need. A needle valve of suitable quality costs well over $100. Still needs a regulator. Let's see..... less complex, less expensive, less bulky, does the job: I think I'll stick with the orifice, thanks.

Those that say that a needle valve allows deeper diving are not thinking straight. All a fixed orifice user does is to select a smaller orifice and use a higher pressure to feed it. Not rocket science. Bottom line is that you pick a reasonable orifice size for the maximum depth of intended use and then match the pressure to it. If you plan to dive much deeper than the depth of flow then simply add a second manual 02 bypass valve from a second 02 supply. You ought to have that for anything that deep anyhow. Really, if you want to dive deeper than the flow depth using either a needle valve *or* an orifice, just let the PP02 slide down during the (short) time on the bottom and refresh PP02 with a nose dump and a diluent add. Assuming that you have a *correct* diluent, you can raise the PP02 with ease using diluent only. If you cannot, your diluent is too lean and you need to start thinking more and adding hardware less.

I'm not even going to address the diver who uses a constant ambient pressure regulator (IE unblocked first stage) with a needle valve. That's really silly, and with all due respect it's not a sensible way to dive. You would be better off with just a straight manual 02 add valve and nothing else. At least there is no possibility of uncertainty as to what the thing is doing. And, in fact, I STRONGLY recommed that first experiences with these things ALWAYS be with a straight manual add valve and NO AUTOMATIC 02 FEED. Get to learn how much 02 you need to add manually b efore you start automating the thing. It's a great lesson to learn and will stand you well over time no matter what rig you dive.

And guys, tuning these systems "too close" is a fallavcy also. The flow NEEDS to be less than your need. Anywhere between 0 LPM flow and about 5/8 of your normal use is just fine. You WANT to be adding 02 manually every 5-10 minutes. That keeps your brain "in the loop".

Dave

bletso · 18th February 2007, 13:08

Dave,

As usual you hit the nail on the head. I just don't understand all the noise of making something so apparent and simple, complicated and more prone to failure. (whether mechanical, electrical or human)

Dale

Tom Rose · 18th February 2007, 13:16

Quote: (Originally Posted by Dave Sutton)

And guys, tuning these systems "too close" is a fallavcy also. The flow NEEDS to be less than your need. Anywhere between 0 LPM flow and about 5/8 of your normal use is just fine. You WANT to be adding 02 manually every 5-10 minutes. That keeps your brain "in the loop".

Dave

Pay attention to Dave's point guys. Dave is right on....operating at .9 liters per minute can be a problem if you are very still on the bottom shooting video. This is one of the reasons I have gone to a lower flow fixed orifice from the RGU system. I found that my PPO was creeping up on me when I was still in the water. I would much rather add O2 more often than to do a partial flush of the loop and add more air to bring down the PPO. That takes more time and wastes gas.

If you are not a gauge watcher...it will be EIA (Evolution in Action)

Tom Rose

gibbogeo · 18th February 2007, 15:41

Quote: (Originally Posted by Dave Sutton)

I'm not even going to address the diver who uses a constant ambient pressure regulator (IE unblocked first stage) with a needle valve. That's really silly, and with all due respect it's not a sensible way to dive.

Ehm, i am interested to hear your point of view about this matter.

I have hear many people swearing that they flow doesn't increase with the dept, using some sort of metering valve and a normal first stage not blocked.

I am buying some part from ebay (when they are very cheap, at least) to test it in a controlled situation, but still i need some parts to set it up completely.

But i am intersted to hear if there is some thing that support theoreticaly the story of the non increasing flow in depth.

I have heard someone talking about viscosity, some other about mass and speed of sound varying...

If you can help, it would be appreciate.

Thank you.

**Dave Sutton** · 19th February 2007, 00:46

Quote: (Originally Posted by gibbogeo)

Ehm, i am interested to hear your point of view about this matter.I have hear many people swearing that they flow doesn't increase with the dept, using some sort of metering valve and a normal first stage not blocked.

In a word: Maybe. There *are* systems that are non-sensitive to both upstream supply pressure and downstream pressure, but they are designed for the science lab and not for the open ocean. Trust me on this though: Why would you want a complex piece of lab equipment so you can say "I didn't need to block my first stage" when a bit of delrin made as a plug will do the same thing with a fixed orifice?

If they are simply saying that they use an adjustable needle valve and actually throttle the 02 flow as they descend, let me use one word: Inefficient. I could use 1000 more words, but it would be a waste of time. It's just not a practical method due to the time duration before seeing the feedback signal (increasing or decreasing PP02) during a *real* dive.

Don't reinvent the wheel. Round wheels work. Start with a simple manual add valve, master it, and then work from there. When you are ready to move on, use a fixed orifice, set the flow to about 0.6 LPM by adjusting the first stage pressure, and plug the regulator with a cap. It'll work every time.

Best,

Dave

Ben Field · 19th February 2007, 09:52

Interesting and informative thread folks, thanks.

Ever so slightly off topic but this thread has the correct minds onboard to comment...

It occurred to me that neither the fixed IP or Balanced to Ambient IP reg are optimal for the fixed orifice MCCR, one provides a supply which dwindles to nothing and the other one which climbs to high to quickly.

Correct me if I'm wrong but once a suitable orifice is selected an acceptable flow rate could be achieved for any depth by altering the supply pressure?

(Perhaps there are certain very high and low pressure flow conditions that give a max and min valve for any given sized orifice but I suspect they may be beyond the pressures most of us are concerned with?)

Perhaps what is needed is a custom first stage that's output is relative to ambient pressure but in a scale that is relavent to flow through an orifice?

What I am saying (badly) is that if you can draw a line on a graph to describe the ideal supply pressure for an orifice (whether it be constant or changing with depth) I see no reason why it cannot be mechanically generated.

Perhaps the changes required are as simple as a 1st stage with a softer spring or as complex as a mechanical system to alter the IP settings relative to depth (some bellows and an allen key?

)

Your thoughts? (Am I on to something or missing an obvious physical limit somewhere?)

regards,
BEN

**Dave Sutton** · 19th February 2007, 10:40

[quote=Ben Field;97290]Your thoughts? (Am I on to something or missing an obvious physical limit somewhere?)

Yes: The first "S" in KISS

Keep
It
SIMPLE
Stupid!

This is life support equipment. Simple = good. We want to REMOVE parts and REMOVE complexity, not add more.

Gorschkov, the father of the modern Soviet Navy had it right. He famously said:

"Better is the enemy of good enough"

More and more = less. A MANUAL 02 INJECTION REBREATHER without any bleed orifice at all is PERFECTLY FUNCTIONAL. Adding a small bleed to the system just makes it a little better. Anything past that drives it into decreasing returns *immediately* and then very quickly after that into decreased desirability *in very short order*.

Leave well enough alone.

"Correct me if I'm wrong but once a suitable orifice is selected an acceptable flow rate could be achieved for any depth by altering the supply pressure?"

Uhhh....... with a blocked first stage, as referenced to outside water pressure, that's *exactly* what is happening in a KISS system already. Mass is constant while volume decreases. 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

Ben Field · 19th February 2007, 11:19

Quote: (Originally Posted by Dave Sutton)

Yes: The first "S" in KISS

Thanks Dave.... I should have prefaced this by saying I was just theortically speaking.

People are constantly farting around with needle valves and second O2 supplies and the like to increase the range of the standard KISS MAV design.

What I was thinking about was taking a step back- not adding complexity but fixing the cause of the foreseen (by some) problem- that the fixed IP causes the flow (of mass) to decrease with and then stop with depth.

Quote: (Originally Posted by Dave Sutton)

This is life support equipment. Simple = good. We want to REMOVE parts and REMOVE complexity, not add more.

Agreed, in fact I couldn't agree more....

However if we stop questioning the accepted then we wouldn't move on... Gordon is a fine example of questioning the accepted- I'm sure thats how he came up with the KISS Rebreather in the first place!

I think you would agree that "changing" a part does not increase complexity but maintains the situation as is? I know the system I'm alluding to does not exist but you have to ask first

Quote: (Originally Posted by Dave Sutton)

Uhhh....... with a blocked first stage, as referenced to outside water pressure, that's *exactly* what is happening in a KISS system already. Mass is constant while volume decreases.

Sorry, sorry... Mass rather than flow, bad word usage, however no flow= no mass so essentially my comment stands? Because we don't have a constant mass system, it decreases and stops... nothing constant about it? (Please again, correct me- I thinking aloud here)

We have a system which is good, simple and apparently flawless.... but it stops functioning at a certain pressure which is not ideal.

What I was trying to ask was actually a simple question-

"If you leave everything as is but allow the IP to be adjusted relative to ambient pressure (in some new as yet undefined way) could the leaky orifice system be made ideal for ALL depths?"

18th February 2007, 08:07	#21 (permalink)
jmurba wet bear Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: May 2006 Location: cannes france Posts: 925	Re: constant IP regs, piston vs diaphragm Quote: (Originally Posted by wedivebc) If you are using an adjustable needle valve why do you even need constant IP? Not to have to tune the flow rate on the fly of course I use to do this with a swagelock needle valve it was great, the valve was in the dolphin shell but the hyrogom valve is better cause the 2 O2 addition modes are in only one set (constant and demand). regards jean mi __________________ when will I be able to think about something else then spending hours underwater, when will I be normal ? http://web.mac.com/jmurba/Site_2/home.html http://web.mac.com/jmurba/Site_3/home.html
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18th February 2007, 08:26	#22 (permalink)
jmurba wet bear Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: May 2006 Location: cannes france Posts: 925	Re: constant IP regs, piston vs diaphragm Quote: (Originally Posted by wedivebc) Which is the whole point of using an adjustable needle valve. Orifice type leaky valve rebreathers are depth limited by the constant IP, adjustable needle valves aren't. Why use a needle valve then don't take advantage of that feature? do you dive this way ? in my opinion tunning the flow rate underwater is a difficult task ins't it ? regards jean mi __________________ when will I be able to think about something else then spending hours underwater, when will I be normal ? http://web.mac.com/jmurba/Site_2/home.html http://web.mac.com/jmurba/Site_3/home.html
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18th February 2007, 12:39	#23 (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 OceanOpportunity) in the case of needle valves, are these being referred to as a device that also restricts flow within a certain range, or a means to control the full spectrum from 'on' to 'off' with the IP flow from the LP hose? In other words, is the needle valve being used in conjunction with an orifice that say offers a max flow of 1lpm or thereabouts on the high end, so it can be tuned down during the dive to adjust for the IP increase on descent? Not really...... these systems should never need to be managed during the dive. If you need to manage the system, it's no longer "simple", stupid! There are two schools of thought: (1): Fixed orifice, pick a size, and then adjust the first stage supply pressure to obtain the feed you desire. (2): Adjustable orifice (needle valve): Set "some" regulator supply pressure and then adjust the valve to obtain the desired flow. The fallacy is the idea that the needle valve ought to be managed during the dive. Those guys who "get it" use the needle valve during setup and then forget it. Those guys who "don't get it" are fiddling with the valve underwater. The problem is that the PP02 change rate response time is not short enough for the diver to be able to use feedback to adjust the valve in anywhere near real-time. I am, personally, firmly in the case (1) mindset. I simply leave the orifice alone and use a hex key to adjust the flow. And since I do that about once a year, it does not seem to me to be worthwhile to have a far more comlex (and expensive) needle valve that I never need to adjust. The orifice I use costs me about $10.00. All diaphram regulators adjust with a key. I have all I need. A needle valve of suitable quality costs well over $100. Still needs a regulator. Let's see..... less complex, less expensive, less bulky, does the job: I think I'll stick with the orifice, thanks. Those that say that a needle valve allows deeper diving are not thinking straight. All a fixed orifice user does is to select a smaller orifice and use a higher pressure to feed it. Not rocket science. Bottom line is that you pick a reasonable orifice size for the maximum depth of intended use and then match the pressure to it. If you plan to dive much deeper than the depth of flow then simply add a second manual 02 bypass valve from a second 02 supply. You ought to have that for anything that deep anyhow. Really, if you want to dive deeper than the flow depth using either a needle valve or an orifice, just let the PP02 slide down during the (short) time on the bottom and refresh PP02 with a nose dump and a diluent add. Assuming that you have a correct diluent, you can raise the PP02 with ease using diluent only. If you cannot, your diluent is too lean and you need to start thinking more and adding hardware less. I'm not even going to address the diver who uses a constant ambient pressure regulator (IE unblocked first stage) with a needle valve. That's really silly, and with all due respect it's not a sensible way to dive. You would be better off with just a straight manual 02 add valve and nothing else. At least there is no possibility of uncertainty as to what the thing is doing. And, in fact, I STRONGLY recommed that first experiences with these things ALWAYS be with a straight manual add valve and NO AUTOMATIC 02 FEED. Get to learn how much 02 you need to add manually b efore you start automating the thing. It's a great lesson to learn and will stand you well over time no matter what rig you dive. And guys, tuning these systems "too close" is a fallavcy also. The flow NEEDS to be less than your need. Anywhere between 0 LPM flow and about 5/8 of your normal use is just fine. You WANT to be adding 02 manually every 5-10 minutes. That keeps your brain "in the loop". Dave __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com Last edited by Dave Sutton : 18th February 2007 at 12:49.
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18th February 2007, 13:08	#24 (permalink)
bletso An independent diver. Current Rebreather/s: Dolphin Home Build Other Rebreather/s: Dolphin Home Build Join Date: May 2006 Location: Louisville, KY, USA Posts: 263	Re: constant IP regs, piston vs diaphragm Dave, As usual you hit the nail on the head. I just don't understand all the noise of making something so apparent and simple, complicated and more prone to failure. (whether mechanical, electrical or human) Dale
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18th February 2007, 13:16	#25 (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) And guys, tuning these systems "too close" is a fallavcy also. The flow NEEDS to be less than your need. Anywhere between 0 LPM flow and about 5/8 of your normal use is just fine. You WANT to be adding 02 manually every 5-10 minutes. That keeps your brain "in the loop". Dave Pay attention to Dave's point guys. Dave is right on....operating at .9 liters per minute can be a problem if you are very still on the bottom shooting video. This is one of the reasons I have gone to a lower flow fixed orifice from the RGU system. I found that my PPO was creeping up on me when I was still in the water. I would much rather add O2 more often than to do a partial flush of the loop and add more air to bring down the PPO. That takes more time and wastes gas. If you are not a gauge watcher...it will be EIA (Evolution in Action) 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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18th February 2007, 15:41	#26 (permalink)
gibbogeo Gilberto Bonaga, Italy Current Rebreather/s: Classic Kiss Dolphin Home Build Other Rebreather/s: Dolphin Home Build Join Date: Sep 2005 Location: italy Posts: 333	Re: constant IP regs, piston vs diaphragm Quote: (Originally Posted by Dave Sutton) I'm not even going to address the diver who uses a constant ambient pressure regulator (IE unblocked first stage) with a needle valve. That's really silly, and with all due respect it's not a sensible way to dive. Ehm, i am interested to hear your point of view about this matter. I have hear many people swearing that they flow doesn't increase with the dept, using some sort of metering valve and a normal first stage not blocked. I am buying some part from ebay (when they are very cheap, at least) to test it in a controlled situation, but still i need some parts to set it up completely. But i am intersted to hear if there is some thing that support theoreticaly the story of the non increasing flow in depth. I have heard someone talking about viscosity, some other about mass and speed of sound varying... If you can help, it would be appreciate. Thank you.
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19th February 2007, 00:46	#27 (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 gibbogeo) Ehm, i am interested to hear your point of view about this matter.I have hear many people swearing that they flow doesn't increase with the dept, using some sort of metering valve and a normal first stage not blocked. In a word: Maybe. There are systems that are non-sensitive to both upstream supply pressure and downstream pressure, but they are designed for the science lab and not for the open ocean. Trust me on this though: Why would you want a complex piece of lab equipment so you can say "I didn't need to block my first stage" when a bit of delrin made as a plug will do the same thing with a fixed orifice? If they are simply saying that they use an adjustable needle valve and actually throttle the 02 flow as they descend, let me use one word: Inefficient. I could use 1000 more words, but it would be a waste of time. It's just not a practical method due to the time duration before seeing the feedback signal (increasing or decreasing PP02) during a real dive. Don't reinvent the wheel. Round wheels work. Start with a simple manual add valve, master it, and then work from there. When you are ready to move on, use a fixed orifice, set the flow to about 0.6 LPM by adjusting the first stage pressure, and plug the regulator with a cap. It'll work every time. Best, Dave __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com
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19th February 2007, 09:52	#28 (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 Interesting and informative thread folks, thanks. Ever so slightly off topic but this thread has the correct minds onboard to comment... It occurred to me that neither the fixed IP or Balanced to Ambient IP reg are optimal for the fixed orifice MCCR, one provides a supply which dwindles to nothing and the other one which climbs to high to quickly. Correct me if I'm wrong but once a suitable orifice is selected an acceptable flow rate could be achieved for any depth by altering the supply pressure? (Perhaps there are certain very high and low pressure flow conditions that give a max and min valve for any given sized orifice but I suspect they may be beyond the pressures most of us are concerned with?) Perhaps what is needed is a custom first stage that's output is relative to ambient pressure but in a scale that is relavent to flow through an orifice? What I am saying (badly) is that if you can draw a line on a graph to describe the ideal supply pressure for an orifice (whether it be constant or changing with depth) I see no reason why it cannot be mechanically generated. Perhaps the changes required are as simple as a 1st stage with a softer spring or as complex as a mechanical system to alter the IP settings relative to depth (some bellows and an allen key? ) Your thoughts? (Am I on to something or missing an obvious physical limit somewhere?) regards, 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, 10:40	#29 (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=Ben Field;97290]Your thoughts? (Am I on to something or missing an obvious physical limit somewhere?) Yes: The first "S" in KISS Keep It SIMPLE Stupid! This is life support equipment. Simple = good. We want to REMOVE parts and REMOVE complexity, not add more. Gorschkov, the father of the modern Soviet Navy had it right. He famously said: "Better is the enemy of good enough" More and more = less. A MANUAL 02 INJECTION REBREATHER without any bleed orifice at all is PERFECTLY FUNCTIONAL. Adding a small bleed to the system just makes it a little better. Anything past that drives it into decreasing returns immediately and then very quickly after that into decreased desirability in very short order. Leave well enough alone. "Correct me if I'm wrong but once a suitable orifice is selected an acceptable flow rate could be achieved for any depth by altering the supply pressure?" Uhhh....... with a blocked first stage, as referenced to outside water pressure, that's exactly what is happening in a KISS system already. Mass is constant while volume decreases. 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 __________________ "Silent Diving with No Bubbles and No Politics".... www.nobubblediving.com Last edited by Dave Sutton : 19th February 2007 at 10:45.
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19th February 2007, 11:19	#30 (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 Quote: (Originally Posted by Dave Sutton) Yes: The first "S" in KISS Thanks Dave.... I should have prefaced this by saying I was just theortically speaking. People are constantly farting around with needle valves and second O2 supplies and the like to increase the range of the standard KISS MAV design. What I was thinking about was taking a step back- not adding complexity but fixing the cause of the foreseen (by some) problem- that the fixed IP causes the flow (of mass) to decrease with and then stop with depth. Quote: (Originally Posted by Dave Sutton) This is life support equipment. Simple = good. We want to REMOVE parts and REMOVE complexity, not add more. Agreed, in fact I couldn't agree more.... However if we stop questioning the accepted then we wouldn't move on... Gordon is a fine example of questioning the accepted- I'm sure thats how he came up with the KISS Rebreather in the first place! I think you would agree that "changing" a part does not increase complexity but maintains the situation as is? I know the system I'm alluding to does not exist but you have to ask first Quote: (Originally Posted by Dave Sutton) Uhhh....... with a blocked first stage, as referenced to outside water pressure, that's exactly what is happening in a KISS system already. Mass is constant while volume decreases. Sorry, sorry... Mass rather than flow, bad word usage, however no flow= no mass so essentially my comment stands? Because we don't have a constant mass system, it decreases and stops... nothing constant about it? (Please again, correct me- I thinking aloud here) We have a system which is good, simple and apparently flawless.... but it stops functioning at a certain pressure which is not ideal. What I was trying to ask was actually a simple question- "If you leave everything as is but allow the IP to be adjusted relative to ambient pressure (in some new as yet undefined way) could the leaky orifice system be made ideal for ALL depths?" __________________ 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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