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reefrat
August 16th, 2013, 10:21 AM
On impulse, and for no good reason other than a hyperactive sense of nostalgia I just paid (probably too much) for a Conshelf Supreme in what appears to be very good condition.
I haven't received it yet but looking at the pictures I see the yoke is stamped 4000 PSI service, was this typical of the Supreme model?

Also, does anyone know how the Conshelf first stage compares with more current diaphragm designs- in terms of the much vaunted flow rate and IP drop during inhalation.
I know that they are very reliable and the service kit is the same as current Aqualung units but maybe there are differences in case design that would affect first stage performance?

regulator bj
August 16th, 2013, 11:30 AM
Have posted some pics to help, is this the unit ?163466163467

reefrat
August 16th, 2013, 12:13 PM
I have tried to post some pics but not sure it worked? The first stage is a typical Conshelf shape and the second stage exhaust tee looks different on yours- but it could just be the angle!

rsingler
August 16th, 2013, 12:32 PM
I haven't received it yet but looking at the pictures I see the yoke is stamped 4000 PSI service, was this typical of the Supreme model?


SE models were 4000 psi regs. One reason to consider the SEs over the venerable XIV, but I'll bet the XIV's 3000 psi yoke works just fine with a 3442 tank, assuming it was yoke and not DIN. I use an SE2 with my old PST 100's (3500 psi).


Also, does anyone know how the Conshelf first stage compares with more current diaphragm designs- in terms of the much vaunted flow rate and IP drop during inhalation.

IMHO, no diaphragm compares to a Poseidon diaphragm for flow. Take the orifices apart, and you'll see what I mean. But I'm open to others' different experience. Get a used 2960 off EBay and see what I mean. Even the old Poseidon unbalanced diaphragm 300's (Model 2305) down-tuned to 130 psi Intermediate Pressure (at near-empty tank) do better than the Conshelf with a balanced second stage. But military units have used both Poseidon and Conshelf.

Fishpie
August 16th, 2013, 12:55 PM
The Supreme is the enviro sealed version of the 1st stage.....can be 14 through to 30.
The older USD ones use an oil cap and the newer AquaLung ones use the Apeks type dry seal.

For me the two least desirable Conshelf 1st stages are the SE and the Flying Saucer (30, PRO or Royal). Not because of any inferiority in their performance but simply due them having all their LP ports sized 1/2" (SE2 and 3 just have the one 1/2" port).
The 21 and 22 are my Conshelf of choice as they have 4 3/8" LP ports and are smaller and lighter than the ones with 1/2" ports.

All Conshelfs will have a similar performance to the 1st generation Titan and Mares MR12.

Most manufacturers have switched to a T shaped design for their diaphragm regs. I suspect this allows for a better air flow and gives more room to provide 2 HP ports.

Luis H
August 17th, 2013, 09:16 AM
I have several Conshelf yokes that were stamped 4000 psi and many with the 3000 psi. They are exactly the same yoke. There are no dimensions or material change between the two. It is just a change in the times… yokes were considered acceptable for higher pressures at one time (Cousteau used 5000 psi yoke tanks for a while).






IMHO, no diaphragm compares to a Poseidon diaphragm for flow. Take the orifices apart, and you'll see what I mean. But I'm open to others' different experience. Get a used 2960 off EBay and see what I mean. Even the old Poseidon unbalanced diaphragm 300's (Model 2305) down-tuned to 130 psi Intermediate Pressure (at near-empty tank) do better than the Conshelf with a balanced second stage. But military units have used both Poseidon and Conshelf.

That is a very interesting observation and I agree that the Poseidon Cyklon 300 has a large first stage orifice. This does rebound the IP very quickly during the breathing cycle. The trade off is that having a large orifice in an unbalanced first stage, causes a larger IP change as a function of tank pressure change. The reason most non-balanced regulators have a small orifice is to try to limit the intermediate pressure swing as a function of tank pressure change. The larger the orifice in a non-balanced first stage, the more it is affected by tank pressure.

It has been over two decades since I service a Cyklon 300 first stage, but I do recall that the IP does change a lot with the change in tank pressure (back then I didn’t actually wrote down this type of data).

I have several Poseidon Cyklon second stage (I have retired their first stage) and I have paired them up with Conshelf first stages. It is easy to adjust the Conshelf to the higher pressure and I like the consistent performance of a constant IP (independent of tank pressure). It makes it a lot easier to fine tune this regulator combination.

I have serviced a lot of Poseidon regulators (in the early 70’s in my first job at Divers Service Center in PR) and I spent a lot of time fine tuning does regulator. We did have a work bench with a regulator to supply any tank pressure I dial in, but it still was more time consuming than other regulators.

My favorite (single hose) regulator back then was the Poseidon, due to its performance (followed by the Scubapro Mk-5).

Note: I also have a bunch of Scubapro 109 second stages and they are all paired up with Conshelf or Aqua Lung Titan first stages. I find their performance being fantastic, perhaps not as good as a flow through piston, but more than adequate for feeding a couple of second stages at the same time.

In my case one of the major advantage with the Conshelf is the commonality of parts with my Royal Aqua Master, Phoenix Royal Aqua Master, etc.

The only job of a first stage is to try and maintain as constant of an IP as possible. The IP will always dip some in all first stages during the breathing cycle. The only advantage of a “higher flow” first stage is that the IP recovery will be a bit quicker and the total drop will be less. I have tested the Conshelf (and its many derivatives) for many decades and I find them all good to excellent performance.

As I mentioned, the flow through pistons are better, but the Conshelf performance are excellent.

I can’t remember the actual flow rate numbers published for flow through pistons and diaphragm regulators. What I recall is that the flow through pistons are several times the max flow of a diaphragm, but either are like an order of magnitude (10x) the flow that any second stage can use. Those flow rate test are only comparative tests and only give a relative idea of first stage performance during actual operation.




Most manufacturers have switched to a T shaped design for their diaphragm regs. I suspect this allows for a better air flow and gives more room to provide 2 HP ports.

I am almost certain that the reason for the change is for ease of maintenance and assembly. I have assembled many Conshelf with a wooden dowel, but it is a lot easier with the special assembly tool (like the one Herman makes). My observation with the “T” geometry is that it doesn’t require any special assemble tools (but I have limited experience with most of the newer first stages).

I don’t believe that the flow rate is any better with the geometry change, at least nothing significant.

rsingler
August 17th, 2013, 11:26 AM
Luis,
Here's a question halocline and I were debating awhile back: even though the flow through a small orifice first stage diaphragm reg is adequate by an order of magnitude, does the drop in dynamic IP affect how well a second stage attached to that reg breathes? In other words, paired in the worst case with a plain downstream second, will a reg that shows a big drop in dynamic IP actually make that reg harder to breathe?
Subjectively, we couldn't feel it. But there's no doubt that a downstream unbalanced second takes more effort to crack at lower IPs.
We wrote it off to a bad sampling location, and guessed that we didn't REALLY have that big a drop in dynamic IP, that's why we couldn't feel any difference. But I'm not so sure it wasn't a real dynamic IP drop we were seeing.
But maybe, since the initial static IP is okay, the unbalanced second cracks normally, and then even a big drop in supply pressure doesn't affect breathing once it's open? I dunno. I'm struggling with this one. We were discussing why some regs (Mk10) seem to show such a big drop in IP on breathing, yet clearly perform as well or better than a Mk5 that doesn't show such a big drop.

Now we've really hijacked this guy's thread, lol!

Luis H
August 17th, 2013, 02:07 PM
The simple initial answer is: yes, with a basic downstream demand valve the drop in IP will affect “work of breathing” (to some degree).

It will not affect the initial cracking suction since the drop in IP only comes into play once flow is initiated.

With a balanced second stage the drop in IP has very little effect.

Then even a basic down stream second stage that is well designed, will have a good venturi effect that will often compensate very well, for the extra vacuum required to keep the demand valve open (due to the momentary drop in IP).

For the most part (within reasonable limits) the design of the second stage plays a much bigger role on the breathing performance of a regulator than the first stage.


I hope this helps and it is clear.

rsingler
August 17th, 2013, 06:39 PM
I think I'll throw a few on the flow bench and see if I can't pin this down. Then we can discuss some more. I'll start a new thread when I get some measurements done.
And I'll put an old Poseidon on the variable tank regulator and get the IP spread compared with one of their balanced models.

Rob

Luis H
August 17th, 2013, 07:36 PM
Keep in mind that the IP drop is a transient/ dynamic flow response, just like the venturi flow in the second stage.

If you have the typical flow bench found in most dive shops, you probably donít have a breathing cycle simulator. Without a breathing cycle simulator (like the ones used in ANSTI machines or at the Navy Experimental Diving Unit), it is very difficult to get significant data of the dynamic response of a regulator.

You can develop a pretty good feel of dynamic flow response of a regulator, but without a repeatable simulator, there is no practical way of obtaining significant quantifiable data.


While visiting the NEDU (Navy Experimental Diving Unit) I got to see several breathing simulators. They were basically large pneumatic piston driven by actuators that could be program to produce a desirable cyclic flow. Normally they test breathing system (rebreathers and open circuit) with a sine wave cyclic flow.

A very interesting comment from one of the lab technicians was that they have actually programmed a different cyclic wave form to more closely simulate the actual human breathing cycle, but at the end the simple sine wave was close enough for most test, and I am sure it is a lot easier to consistently produce a sine wave to obtain repeatable results.


Rob
As a USAF hyperbaric officer, I am guessing that you are far more familiar with human breathing cycle than I amÖ I just deal with fluid dynamics from an engineering perspective... and when it comes to fluid dynamics, some of the real experts will tell you that accurate prediction can involve some witchcraft and magic.
:D

reefrat
August 17th, 2013, 08:48 PM
I think Luis is right about the second stage being more important for WOB and first stage IP drop playing a bigger part than the flow rate. I seem to recall reading a number of times way back about people over-breathing regulators, particularly at depth. I have read more recently reviewers make comments about far regs have come in terms of breathing performance in the last 20 years! The curious thing is that when you look at the numbers there doesn't to be much difference.
Take for example the Conshelf first stage, I have seen the flow rate quoted as about 50 scfm and this unit has been around for nearly 40 years (AFAIK). The new Titan first stage combined with a Titan LX second stage has been described as a good breather with very good reserves for deepish diving, well turns out that (according to an Aqualung website I found) it's flow rate is 1450 L/min which equates to about 50 scfm, the same as the Conshelf. Even the new top of the line Aqualung Legend first stage is only a smidge more- under 60 scfm! The Poseidon Xstream first stage is toted as a deep technical unit- for use to 200m on trimix, it's flow rate is about 76 scfm and the older Cyclon wasn't much more than half this.
Of course we all know that Scubapro quotes huge flow rates for their first stages but does it really make any difference when the US Navy manual says that a super fit naval diver doing "severe work" uses about 1.9 to 3.5 cfm (presumably at the surface). In fact I'll bet that Scubapro's (and maybe all manufacturers) flow rates are based on the combined flow of all the low pressure ports venting simultaneously when really what counts is the flow that is delivered to the primary first stage and how little IP drop there is during the cycle. It may also be that the number of low pressure ports a first stage has (5 on the MK25 and 3 on the Conshelf) has a bearing on the flow rate figure?
Anyway, I tried out a Conshelf XIV second today on a Mares MR22 first and it worked really well- maybe the Mares DFC (first stage venturi effect) really does work, but that is probably another thread on a different forum?

John C. Ratliff
August 17th, 2013, 09:54 PM
Luis and Rob,

This is a very interesting discussion. I would like to add two points.

http://i3.photobucket.com/albums/y76/yaquinaguy/UDS-1diagram.jpg (http://s3.photobucket.com/user/yaquinaguy/media/UDS-1diagram.jpg.html)
First, I have a UDS-1 diving system by U.S. Divers Company from the 1980s. Unfortunately, I cannot now dive it as it has one-inch openings on the three aluminum cylinders, and nobody has an eddy current tester for it. So I cannot get the cylinders hydroed and therefore the unit filled. But, I have dived it many times, and this unit has the largest openings of any unit for air flow. The first stage, Conshelf-style first stage built into the triple cylinder valve. Because of this design, there is no regulator/valve interface, and the openings are very, very large.
http://i3.photobucket.com/albums/y76/yaquinaguy/UDS-1manifoldreserveend1.jpg (http://s3.photobucket.com/user/yaquinaguy/media/UDS-1manifoldreserveend1.jpg.html)
The Scubapro A.I.R. I regulator has the ability to use two hoses going into the second stage.
http://i3.photobucket.com/albums/y76/yaquinaguy/AIR-1AddendumFigure1.jpg (http://s3.photobucket.com/user/yaquinaguy/media/AIR-1AddendumFigure1.jpg.html)
This allows the use of two regulators, with a doubling effectively of the surface area for the openings and a doubling of the volume of the two hoses, both of which decreases the interstage pressure drop. Here is the Scubapro graph of the breathing cycle of the A.I.R. I:http://i3.photobucket.com/albums/y76/yaquinaguy/AIR-1SecondStagePerformance.jpg (http://s3.photobucket.com/user/yaquinaguy/media/AIR-1SecondStagePerformance.jpg.html)

I combined these two concepts, and mated the A.I.R. I with the UDS-1. http://i3.photobucket.com/albums/y76/yaquinaguy/UDS1bal.jpg (http://s3.photobucket.com/user/yaquinaguy/media/UDS1bal.jpg.html)
At one point I took it one step further, and used two hoses on the LP side of the UDS-1 (there is an auxiliary port for a tool, which I used that comes from the manifold) into the A.I.R. I second stage. That was amazing as a breathing machine. Even with the USD second stage, I could breath this unit down to zero gauge pressure before feeling a breathing resistance.

SeaRat

rsingler
August 18th, 2013, 02:11 AM
This AIR1 stuff is great data. And I think it gives us half of the answer we're looking for. I'm not sure we need a WOB loop to answer the rest of this question, and your AIR1 loops tell us why.

First, a roughly sinusoidal breathing pattern isn't too far off. It just needs to be squared a little bit. The point is that as you inhale a big (2 litre) breath, it starts slowly, accelerates, plateaus and ends. Then exhalation starts, but we'll ignore that. So if inspiration is half of a breathing cycle, the accelerated portion of an inhaled breath is perhaps 80% of that half cycle, or 40% of a full breathing cycle.

Let's do a little math for a heavy exertion situation:
Big guy breathing 50 breaths per minute (and he can't keep that up for long, but we want to see what his equipment does). What is the max flow rate during inhalation?
50 bpm = 1.2 sec per breath cycle.
If the accelerated inhalation (max flow) is 40% of the cycle, then the max flow portion takes .4 x 1.2 or .48 sec.
Let's assume our big guy is able to take in 80% of his breath during the accelerated portion, and only 20% is inhaled during the slower beginning and end of an inhaled breath. I'm being generous with this sine wave. Eighty percent of his 2 liter breath is 1.6 liters.

So the maximum flow (at the surface) for this big guy is 1.6 liters in 0.48 sec.
That computes out to 200 liters/minute, or 7 SCFM. This fits quite nicely into the data quoted above about the super fit Navy diver consuming 1.9 to 3.5 SCFM. Since he's inhaling 40% of that time, his max flow is 3.5 SCFM divided by 0.4 or 8.75 SCFM max flow. This tells us that our flow guess is about right.

Now let's look at a part of that wonderful AIR1 data above. Look at the top right quadrant of either set of blue loops. As the depth increases, the air gets thicker, and the venturi effects become more pronounced. At the surface, it takes 4 SCFM to pull the reg from a sucking inspiratory effort over into freeflow with a 2000 psi tank. At 100 feet, the thicker air generates a more vigorous venturi effect and the regulator freeflows every time the suck gets faster than about 2 SCFM. This is one of those regulators that gives a positive breath under heavy exertion. That reduces effort, though it's judged a fault for a rec diver. I won't argue that piece. In any case, we never get close to 7 SCFM on these flow loops.

What we DON'T know about these loops, and what a WOB curve doesn't tell us (but a flow bench does, at least at surface air density) is, "What was the dynamic IP during each part of this breath? If we know that an unbalanced second (which the AIR1 ISN'T) is harder to breath at low IP, what would flows look like through that second stage when you change the dynamic IP?
We might be seeing it (but we can't tell) in the two sets of curves for the dive/pre-dive switch. Is the increased effort with the pre-dive switch equivalent to the increased effort we'd see in an unbalanced second with a lower dynamic IP?

We can look at some of that on a flow bench. It's going to take a lot of air, so it'll be awhile before I get the numbers, but here's my project:

1) Assume a good unbalanced second requires 1.0" to crack and requires 0.8" of suck at 4 SCFM and 0.6" at 7 SCFM because of its venturi contribution. Like most regs, it doesn't kick over into freeflow at the surface with anything short of "purge" flows (11-15 SCFM).
2) What was the dynamic IP at 4 and 7 SCFM that gave us those inhalation efforts?
3) If you provide a different first stage with a higher or lower dynamic IP at 4 SCFM, how does the required suck for that flow change?
4) If you provide the same first stage, but adjust the static IP so that the new dynamic IP is equal to the static IP in the previous experiment, does the reg require less suck? Our intuition tells us yes, because we know unbalanced seconds are harder to breathe at lower IPs. But we only have static IP data so far. We don't know what is contributing to the inhalation effort at high flow. Is it just modest venturi effect? Is it a HUGE venturi effect that is counterbalanced by increased inhalation effort due to the drop in dynamic IP? Or does it have nothing to do with IP and is solely a flow limitation from the first stage?
5) And lastly, what happens if we substitute a balanced second? Again, we think we know the answer, because their performance is so much less dependent upon a stable IP.

So that's the plan: determine inhalation resistance at various dynamic IPs. Since we're comparing apples to apples (the same reg tested against itself), the worry that halocline and I had about whether the dynamic IP was real or not won't matter.
Whether it's real or not on the IP gauge, the inhalation resistance under varying conditions will tell us more about the contribution of IP change to breathing resistance. Because we just learned from the great AIR1 data above, that flows at depth will be huge given a good enough 1st.

So if a bigger orifice is associated with bigger IP drops, as Luis suggested above, then the help provided by the improved flow may be canceled out by the greater inhalation resistance (due to the bigger IP drop), and inhalation resistance at 4 and 7 SCFM will not be better with a big orifice 1st stage. At least with an unbalanced second. Which is why AIR1 guys are such fanatics about their regs. :D

More to come...

Luis H
August 18th, 2013, 09:45 AM
So if a bigger orifice is associated with bigger IP drops, as Luis suggested above,

More to come...

That is not what I said. I am sorry if I was not clear.

What I said was in reference to the not-balanced first stage (like the Cyklon 300). A larger orifice in a not-balanced first stage makes the regulator more susceptible to the change in tank pressure. I was not referring to the dynamic IP drop during the breathing cycle.

The IP will change more (with and unbalanced first stage) from a full tank to an empty tank, if the orifice is larger. The smaller orifice is not affected as much from with the change in tank pressure. This is not referring at the flow through the orifice, but just the pneumatic reaction of the pressure times the orifice area.

This does not apply to a balanced first stage. Balanced first stages normally have volcano orifices that are much larger than non-balanced first stages. Balanced first stages are not affected by tank pressure (some are not as well balanced as others).


With all other factors equal, a larger orifice produces less restriction during flow condition.


BTW, I like your analysis of the breathing cycle.







the worry that halocline and I had about whether the dynamic IP was real or not won't matter.



I have no idea what you guys are talking about here… I will have to give Matt a call.

The momentary IP drop is not only measurable, but can also be predicted by solving the differential of Bernoulli’s equation as a function of time, assuming again a sine wave flow change for simplification purposes.



The Air1 is one of the best balanced second stages and it is really not affected by IP changes.

That data is very interesting, but I am not sure how that data was taken. If you look at the X axis it has flow rate, not volumetric change. Even do it talks about 20 BPM, the data seems to be more for steady state flow than for a transient flow distribution.

The curves could be showing the instantaneous flow rate (instantaneous volume change as a function of time), but the curves don't look like they were generated by a breathing simulator. I have seen pictures of the test equipment they used to use, but I have never seen the details.

There is a lot of the old data (including the old Navy EDU) data that was just using steady state flow measurements.

As you mention, that data is valuable, but you need to know how to interpret it and how to use it.

reefrat
August 18th, 2013, 11:29 AM
This AIR1 stuff is great data. And I think it gives us half of the answer we're looking for. I'm not sure we need a WOB loop to answer the rest of this question, and your AIR1 loops tell us why.

First, a roughly sinusoidal breathing pattern isn't too far off. It just needs to be squared a little bit. The point is that as you inhale a big (2 litre) breath, it starts slowly, accelerates, plateaus and ends. Then exhalation starts, but we'll ignore that. So if inspiration is half of a breathing cycle, the accelerated portion of an inhaled breath is perhaps 80% of that half cycle, or 40% of a full breathing cycle.

Let's do a little math for a heavy exertion situation:
Big guy breathing 50 breaths per minute (and he can't keep that up for long, but we want to see what his equipment does). What is the max flow rate during inhalation?
50 bpm = 1.2 sec per breath cycle.
If the accelerated inhalation (max flow) is 40% of the cycle, then the max flow portion takes .4 x 1.2 or .48 sec.
Let's assume our big guy is able to take in 80% of his breath during the accelerated portion, and only 20% is inhaled during the slower beginning and end of an inhaled breath. I'm being generous with this sine wave. Eighty percent of his 2 liter breath is 1.6 liters.

So the maximum flow (at the surface) for this big guy is 1.6 liters in 0.48 sec.
That computes out to 200 liters/minute, or 7 SCFM. This fits quite nicely into the data quoted above about the super fit Navy diver consuming 1.9 to 3.5 SCFM. Since he's inhaling 40% of that time, his max flow is 3.5 SCFM divided by 0.4 or 8.75 SCFM max flow. This tells us that our flow guess is about right.

Now let's look at a part of that wonderful AIR2 data above. Look at the top right quadrant of either set of blue loops. As the depth increases, the air gets thicker, and the venturi effects become more pronounced. At the surface, it takes 4 SCFM to pull the reg from a sucking inspiratory effort over into freeflow with a 2000 psi tank. At 100 feet, the thicker air generates a more vigorous venturi effect and the regulator freeflows every time the suck gets faster than about 2 SCFM. This is one of those regulators that gives a positive breath under heavy exertion. That reduces effort, though it's judged a fault for a rec diver. I won't argue that piece. In any case, we never get close to 7 SCFM on these flow loops.

What we DON'T know about these loops, and what a WOB curve doesn't tell us (but a flow bench does, at least at surface air density) is, "What was the dynamic IP during each part of this breath? If we know that an unbalanced second (which the AIR1 ISN'T) is harder to breath at low IP, what would flows look like through that second stage when you change the dynamic IP?
We might be seeing it (but we can't tell) in the two sets of curves for the dive/pre-dive switch. Is the increased effort with the pre-dive switch equivalent to the increased effort we'd see in an unbalanced second with a lower dynamic IP?

We can look at some of that on a flow bench. It's going to take a lot of air, so it'll be awhile before I get the numbers, but here's my project:

1) Assume a good unbalanced second requires 1.0" to crack and requires 0.8" of suck at 4 SCFM and 0.6" at 7 SCFM because of its venturi contribution. Like most regs, it doesn't kick over into freeflow at the surface with anything short of "purge" flows (11-15 SCFM).
2) What was the dynamic IP at 4 and 7 SCFM that gave us those inhalation efforts?
3) If you provide a different first stage with a higher or lower dynamic IP at 4 SCFM, how does the required suck for that flow change?
4) If you provide the same first stage, but adjust the static IP so that the new dynamic IP is equal to the static IP in the previous experiment, does the reg require less suck? Our intuition tells us yes, because we know unbalanced seconds are harder to breathe at lower IPs. But we only have static IP data so far. We don't know what is contributing to the inhalation effort at high flow. Is it just modest venturi effect? Is it a HUGE venturi effect that is counterbalanced by increased inhalation effort due to the drop in dynamic IP?
5) And lastly, what happens if we substitute a balanced second? Again, we think we know the answer, because their performance is so much less dependent upon a stable IP.

So that's the plan: determine inhalation resistance at various dynamic IPs. Since we're comparing apples to apples (the same reg tested against itself), the worry that halocline and I had about whether the dynamic IP was real or not won't matter.
Whether it's real or not on the IP gauge, the inhalation resistance under varying conditions will tell us more about the contribution of IP change to breathing resistance. Because we just learned from the great AIR1 data above, that flows at depth will be huge given a good enough 1st.

So if a bigger orifice is associated with bigger IP drops, as Luis suggested above, then the help provided by the improved flow may be canceled out by the greater inhalation resistance (due to the bigger IP drop), and inhalation resistance at 4 and 7 SCFM will not be better with a big orifice 1st stage. At least with an unbalanced second. Which is why AIR1 guys are such fanatics about their regs. :D

More to come...

Maybe you could also have a look at the difference (if any) that a 1/2" port and the associated larger diameter hose makes to flow rates and IP drop? These were touted as increasing flow to the second stage and were a selling point on top of the line Aqualung and Mares regs (among others), but went out of favor sometime in the 90's because it was thought that they made no real difference and the DIR long hose users wanted standardized ports (what ever happened to the DIR mob?).

rsingler
August 18th, 2013, 12:34 PM
A larger orifice in a not-balanced first stage makes the regulator more susceptible to the change in tank pressure. I was not referring to the dynamic IP drop during the breathing cycle.

OK, now I'm with you! Sorry about my misunderstanding! I agree with you on orifice and IP change with tank pressure. So far, we're on the same page.



http://www.scubaboard.com/forums/images_sb/misc/quote_icon.png Originally Posted by rsingler http://www.scubaboard.com/forums/images_sb/buttons/viewpost-right.png (http://www.scubaboard.com/forums/vintage-equipment-diving/463165-conshelf-supreme-first-stage-2.html#post6857022)

the worry that halocline and I had about whether the dynamic IP was real or not won't matter.



I have no idea what you guys are talking about here… I will have to give Matt a call.
The momentary IP drop is not only measurable, but can also be predicted by solving the differential of Bernoulli’s equation as a function of time, assuming again a sine wave flow change for simplification purposes.

Luis,
It all started in a discussion about flow benches, when someone observed that a Mk5 appeared to have less of a dynamic IP drop than a MK10, when the flow was so much better in the Mk 10 with its bigger orifice. We didn't test that statement at the time (big mistake), but Halo refused to believe that the Mk 10 performed more poorly than the Mk 5, because the Mk 10's orifices were so much bigger. If dynamic IP was in fact a good measure of performance, he raised the possibility of a measurement error due to a venturi effect in the LP chamber where the gauge was connected. We decided to test the possibility of venturi effects contributing to the dynamic IPs measured, and based on the pictures here, I couldn't say he was wrong, even though the results were a little unsatisfactory.
Here's a Mk5 on a test stand with an unbalanced second stage attached.
163556The larger IP gauge below the Magnehelic is attached to an LP port. But I added a second IP gauge on a T-fitting just below the second stage. The intent was to see if "where the IP gauge was located" (in the second case, OUTSIDE the LP chamber of the Mk 5 and closer to the breathing point) would affect the measured dynamic IP. The hope was that the IP would drop less in the gauge right next to the 2nd, because there wasn't whatever venturi effect might be going on in the LP chamber of the Mk 5, and we were sampling nearer where the diver was breathing. Well, here were the results.
Here's the static IP:
163557 IP of 132 on both gauges at 400psi supply pressure.
And here's the dynamic measurement at high flow (i.e., I hit the purge button)!
163558IP drops to 105 in the turret of the Mk 5, and 75 in the T-fitting!!!

Well, of course in retrospect, it all makes sense. Whether or not there's a venturi effect going on in the turret of the Mk 5, there CERTAINLY is a venturi in the T-fitting. It's a classic fitting in that regard: the sampling port T's off a narrowed waist inside the brass fitting, so of course pressure will drop as the gas races by. Dr. Bernouilli says so.

So that's where it all started.
Luis, sounds like you might be able to give us the answers to our first question:
1) Can you reliably even measure dynamic IP with a gauge on a hose attached to the turret? Or do you need special equipment that eliminates the possibility of a venturi effect somewhere in the measuring system?

But what we should have done was to test the original "observation", that Mk 5's had less of a dynamic IP drop than the Mk 10. As I said before, that was our original mistake before I set off on a tangent about venturi effects and measuring dynamic IP.
Intuitively, it just didn't make sense. It seemed intuitively that if a reg can provide better flow, there should be less of a drop in the supply pressure to the second stage when it's flowing. And yet...there's that Bernouilli thing.

So here are the results when I finally compared the Mk 5 to the Mk 10:
Mk 5 on the bench at 400 psi:
Static 132 psi; Purge IP 98 psi; Change in IP: 34 psi
163561163562
Here's the Mk 10 on the bench, also at 400 psi supply pressure:
Static IP 126psi; Purge IP 104 psi; Change: 22 psi.
163563163564
Yeah, I know. I should have done it on the flowmeter, so the purge flows were comparable, but I'll have to set that up later to confirm.
If these results are equivalent, then the original comment made by someone else was just a rumor repeated so often it became "true." The Mk5 IP doesn't drop less than the better performing Mk10, it drops more. But in any case, the last question still stands:

When the dynamic IP drops, does that contribute significantly to why an unbalanced second stage breathes harder with "cheaper" first stage regulators, because it's seeing a lower supply pressure in mid-breath? Or is it the poorer flow provided by a bad first stage? Which is the governing factor?

Me, I think it's all the IP drop, because the flow at the second (not what the first is capable of) is directly related to input pressure.

rsingler
August 18th, 2013, 01:39 PM
Maybe you could also have a look at the difference (if any) that a 1/2" port and the associated larger diameter hose makes to flow rates and IP drop? These were touted as increasing flow to the second stage and were a selling point on top of the line Aqualung and Mares regs (among others), but went out of favor sometime in the 90's because it was thought that they made no real difference and the DIR long hose users wanted standardized ports (what ever happened to the DIR mob?).

I believe that question has been answered. The Work of Breathing guys can create a situation at depth with thick air and huge flows where a 1/2" vs 3/8" port makes a difference. But for most everything else, it's not noticeable. The first stage is capable of providing more air than most everyone else needs (except the US Navy).

You can also take the Poseidon/Cyklon route and build a reg with a much higher IP. Great flow at depth.

As far as the hose diameter and length goes, there are DIR folks who say you can feel a difference, and physics tells us that there will be more resistance in the longer hose. But again, while I haven't measured it yet, it's probably only significant at high workload/high flow rates and low IP's, as might be set for ice diving. That might be a place for shorter hoses, but then there's the cave thing. But Scubapro agrees with you on hose diameter and resistance. They've marketed the Superflo hose, I think it's called. Once again, the diffs are shown mostly in the lab, except for the guys that can feel the difference.

3D diver
August 18th, 2013, 03:08 PM
Well this thread has legs and has gone in an interesting direction. I'm not sure I have much to contribute but, for the sake of getting it into my subscribed list, here's a pic of my regulators:

http://i1116.photobucket.com/albums/k570/waynebg/SCUBA/regulators_zpsa1f3c75a.jpg (http://s1116.photobucket.com/user/waynebg/media/SCUBA/regulators_zpsa1f3c75a.jpg.html)

My late wife won the USD Royal Aqualung regulator, a tank and BC in 1982 at the grand opening of a dive shop in North Carolina (Waterworld, I believe, near Durham). It breathed nice but few shops could tune it so tended to free flow and was relegated to being my backup setup for many years. Eventually USD issued a recall on the second stage and replaced it with the Conshelf SEA shown (USD wanted $50 for this, but Wallins swapped it for free). It has been my primary setup ever since.

I recently bought some high pressure steel tanks and was concerned about the 3000 psi stamp on the yoke, but this thread has put my mind at ease.

Fishpie
August 18th, 2013, 03:22 PM
The Royal was an interesting 2nd stage.
It was slightly bigger than their standard 2nd stage, had an additional adjustable side exhaust and was USD's only attempt at a balanced 2nd before they adopted the current Apeks design.

John C. Ratliff
August 18th, 2013, 03:55 PM
rsingler,

Thanks for the information and photos of your setup. That tells me a lot.

I am an industrial hygienist by training, and have worked in this field and safety for about 36 years. I am not an engineer like Luis, but my son is so I can bounce things off him. I also have been diving since 1959, and so have seen my share of regulators, and my collection is a good representation of older regulators. So I have some insights others may not have.

I'd like you to go back to your bench, and do something with your regulators and take another set of readings. Switch the primary LP line from the side to the top of the regulator. A stamped, mitered 90 degree turn in an air flow pattern results in a loss coefficient of 2.50 (Figure 9-e, date 1-07, page 9.50 of the ACGIH Signature Publication Industrial Ventilation, A Manual of Recommended Practice for Design, 26th Edition--this is the "Bible" of industrial ventilation). By simply mounting the Mk 5 on top, and the Mk 10 on the side, you may see the results people are talking about for better flow. There is a lot of turbulence set up when you make that 90 degree turn, and this will adversely affect the flow rates you see. Industrial Ventilation says that this condition should be avoided in designing ventilation systems, and it applies here too as Scubapro found out in the 1970s U.S. Navy EDU tests.

The graph I put up comes from the publication, A.I.R. I Air Inhalation Regulator Second Stage, Addendum to TECHNICAL MANUAL for SCUBAPRO REGULATORS (Cat. 45-101-187), with a date of 1979. It came with my A.I.R. I second stage, which I still have and still dive. The top graph states:

TEST DEPTH AS INDICATED Ft/Mt
SUPPLY PRESSURE 300 PSI/ATM
SECONDARY PRESSURE 135 PSI/ATM
TIDAL VOLUME 2 liters
BREATHING RATE 20 BPM
For the bottom graph:

TEST DEPTH AS INDICATED Ft/Mt
SUPPLY PRESSURE 2000 PSI/ATM
SECONDARY PRESSURE 135 PSI/ATM
TIDAL VOLUME 2 liters
BREATHING RATE 20 BPM
This was done by ScubaPro R&D in 1979, using Model 12-126-000, Serial 17779083.

In their "Installation" portion of this publication, Scubapro makes this statement:


The hose may be connected to either the right-hand or the left-hand port of the regulator. The unused port must, of course, be capped with the provided plug. Commercial or advanced divers requiring improved flow performance at depth can connect the A.I.R. I Second Stage to the first stage with two hoses, one over each shoulder. Maximum flow performance and safety can be achieved by attaching the A.I.R. I Second Stage to two independent first stages which, in turn, are mounted on separate high-pressure cylinders.

You talk about the long hoses of the DIR divers as having "increased resistance." I'll let Luis comment on that, but the resistance would be due to turbulence, and this may be overcome by the increase in volume of air available. What Luis is saying about increases drop in IP due to a larger diameter opening makes sense if the hose length and volume is constant in the comparison. But if the volume is increased, the "pool" of air would be increased and I think you'll see that the IP drop is not as great. The same goes for Scuabpro's statement about using two regulators feeding the A.I.R. I Second Stage; not only is the volume increased (doubled), but also the diameter of orifices into the second stage is effectively doubled. I think this is the basis for Scubapro's statement about improved flow rates at depth. The denser gas has much more volume and area to go through.

Concerning the U.S. Navy being the ones needing the increased flow, that simply is not true. An overweighted diver, in poor condition in current in a sport diving situation will have very high respiratory demand. I've seen fatalities from this situation. By the way, breathing at 50 breaths per minute (BPM) is hyperventilation, and actually reduces oxygenation of the blood. This is because this rate dictates a very shallow breath, and you won't get the exchange needed. The use of 20 breaths per minute by Scubapro is based upon research results for active divers, and is more realistic.

SeaRat

rsingler
August 18th, 2013, 04:57 PM
rsingler,
By the way, breathing at 50 breaths per minute (BPM) is hyperventilation, and actually reduces oxygenation of the blood. This is because this rate dictates a very shallow breath, and you won't get the exchange needed. The use of 20 breaths per minute by Scubapro is based upon research results for active divers, and is more realistic.

SeaRat

Thanks, SeaRat! Your AIR-1 data was terrific. Luis' points about flow vs. inhalation resistance not being equivalent to a WOB loop are appropriate, but it's still fascinating data.

I just have to comment on the above. 50 bpm is only hyperventilation when it's not driven by demand. The decreases in oxygenation are driven by the pH change in blood from respiratory alkalosis, if you blow off too much CO2 by hyperventilating. The blood oxygenates okay, but can't offload to the tissues as well when the pH is alkaline. There's also some vasoconstriction that happens when CO2 drops. A big deal in neurosurgery.
But in max effort exercise, your CO2 production is huge, and you need to breathe that much to both acquire O2 for your tissues and to blow off CO2 to preserve normal pH (not including whatever lactic acidosis you acquire from anaerobic metabolism by being unable to breathe enough for the exercise load). So in the hypothetical "big Navy diver", my presumption was that he was breathing 50bpm because he had to. Sorry I didn't make that clear.

"Enough for the USN" was really just a cryptic reference to their standards for military regulator testing at extreme depth and max RMV. Again, sorry for not explaining myself. I certainly agree with the risk to the out-of-shape fat guy outstripping his ability to oxygenate his tissues! Long live drift diving! :)

Doc

John C. Ratliff
August 19th, 2013, 02:33 AM
Doc Rob, at first I did not believe that 50 BPM were possible, and I cited a paper to you in a PM about that, but in the same PM I found this You Tube video of an 800 meter immersion finswimming event, and counted between 40 and 50 BPM. The amazing thing is that the winner swam the race in 5:59.98. Amazing.

https://www.youtube.com/watch?v=RSGpw-ZFWTc

I also note that it appears that the Poseidon regulator was used by at least one contestant. I have a publication comparing the Cyclon 300 with four other regulators, and finding some problems at very low tank pressures (300 psig). The Conshelf XIV, Calypso and A.I.R. 1 on the five port first stage fared well.

SeaRat

reefrat
August 19th, 2013, 08:40 AM
[QUOTE=John C. Ratliff;6858020]Doc Rob, at first I did not believe that 50 BPM were possible, and I cited a paper to you in a PM about that, but in the same PM I found this You Tube video of an 800 meter immersion finswimming event, and counted between 40 and 50 BPM. The amazing thing is that the winner swam the race in 5:59.98. Amazing.

https://www.youtube.com/watch?v=RSGpw-ZFWTc

I didn't know this sport existed- bizarre! Although I did a drift dive recently with a some German tourists and they ended up 1/2 mile further downstream, so maybe it was some of these guy's on vacation?


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