90 degree elbow on second stage

[tursiops]

Just out of curiosity, why then does Scubapro put a port on the top of the cap?

Maybe for better routing of the hose? That is why people use that port, not because it performs better.

Yes, there is a difference between steady flow and unsteady-flow situations, but by citing the ACGIH elbow figure, I point out that any turn in air flow will induce some turbulence, and that will influence the flow. You can actually see that if you look at river flows. Where I dive on the Clackamas River, the river itself makes a 90 degree turn. There is a portion of the current which actually flows upstream, and then comes back in a circular manner downstream. In a like manner, whenever an air flow in a regulator makes a 90 degree turn, that will set up turbulence which will inhibit flow.

The regulator is sometime flowing, sometimes not. There is no turbulence when it is not. it takes a while for the turbulence to start....thus mitigating any estimates based on steady flow. I assume your river does not start and stop?

My only point is that there is some sacrifice in the regulator's performance whenever this is done.

There may be. My point is that if it were perceived to be significant, all those people would not be using elbows.

 

[tbone1004]

Ya, it was the Mark I that was tested, but it also had the port on top. That was my mistake. But, and I don't have time to find the report right now, there have been subsequent EDU tests which validated the top port, I think using the Mark V (or later) and A.I.R. I regulator combination. My argument is also logical, as any turn in a flow will cause turbulence. So it seems that you are saying that the 90 degree turn causes no turbulence, and no impact on flow? Other than subjective impressions, what is your source on that?

SeaRat

the MK1 doesn't count either because it's a completely different regulator, you need to compare apples to apples. That report compared apples to apples and in the realms of any recreational environment, there is no appreciable difference between the two. In the extremes, your argument was disproven.

I'm not saying it doesn't create turbulence, I'm not saying it doesn't increase pressure drop, and I'm not saying it doesn't increase the effective length of the hose. What I'm saying is that the effects are irrelevant, and if they were, then you would see a noticeable difference in work of breathing between a 22" and 84" hose from the friction created going through the hose. We don't, so while it does impact the flow, it does so in an irrelevant manner. Especially since the most common port configuration for the MK25 or any 5 port turret in technical diving is to have the long hose on the side, and the short hose on the bottom port. Those get used every day in deep, high flow caves, and no one has had an issue

 

[John C. Ratliff]

Okay, I've found the NEDU study that I was talking about. Take a look at the regulator performance and work of breathing, and the first stage pressure drop for the 4-port and 5-port Scubapro Mk V regulators with an A.I.R. I second stage. Everything is the same except the 4-port, with the 90 degree turn, and the 5-port, without that turn as the first stage is on the top of the regulator cap. These can be found here:

Evaluation of Commercially Available Open Circuit Scuba Regulators.

If you look at the Scubapro A.I.R. I Second Stage Peerformance Characteristics, you will see that Scubapro uses an intermediate pressure of 135 psig. But with the 4-Port first stage, the Navy EDU graph shows up to a 45 psig pressure loss. In its explanation, they also say, "...When pressure losses approach 40 to 50 psig less than static, the regulator ceases to function in a manner which can effectively support a diver..."

SeaRat

 

[tbone1004]

@John C. Ratliff so at what point do you deem those values relevant and how does that argument apply to the second stage swivel?

I don't think anything over 40lpm/1.4cfm is really relevant, and anything deeper than 132 really isn't relevant since those are outside of the scope of recreational diving.
The pressure drop graphs at that range you chose not to upload, and that has a roughly 25psi ip drop for the 5 port, and 30psi drop for the 4 port. Hardly significant in the scope of work of breathing as shown by the WoB being between .1 and .14 for that test cycle. Much of that can largely be given to the cycle time of the regulator which if you breathed at that rate for any length of time *more than about 30 seconds* would cause you to pass out

So again, how does that chart apply to recreational diving? You posted values for 62.5 and 75 rmv's, can you maintain a SAC rate of 2.5cfm for any duration of time? I highly doubt it.
Do you regularly violate the accepted max depths of recreational diving at 132 where the gas density starts to cause significant variance between the two? I certainly hope not.
Since 40lpm or 1.4cfm is really an elevated SAC rate, do you feel that the difference between a WoB of 0.08 and 0.10 is significant? If so, why?
How do you know that the second stage elbows yield a similar net effect that is measurable and meaningful within the scope of recreational diving?

 

[tursiops]

@John C. Ratliff so at what point do you deem those values relevant and how does that argument apply to the second stage swivel?

I don't think anything over 40lpm/1.4cfm is really relevant, and anything deeper than 132 really isn't relevant since those are outside of the scope of recreational diving.
The pressure drop graphs at that range you chose not to upload, and that has a roughly 25psi ip drop for the 5 port, and 30psi drop for the 4 port. Hardly significant in the scope of work of breathing as shown by the WoB being between .1 and .14 for that test cycle. Much of that can largely be given to the cycle time of the regulator which if you breathed at that rate for any length of time *more than about 30 seconds* would cause you to pass out

So again, how does that chart apply to recreational diving? You posted values for 62.5 and 75 rmv's, can you maintain a SAC rate of 2.5cfm for any duration of time? I highly doubt it.
Do you regularly violate the accepted max depths of recreational diving at 132 where the gas density starts to cause significant variance between the two? I certainly hope not.
Since 40lpm or 1.4cfm is really an elevated SAC rate, do you feel that the difference between a WoB of 0.08 and 0.10 is significant? If so, why?
How do you know that the second stage elbows yield a similar net effect that is measurable and meaningful within the scope of recreational diving?

Interesting report. Two things caught my eye:
(1) The regs had improved a lot in the four years since the previous examination of regs. Makes you wonder if there has been further improvement in the 37 years since that report.
(2) The Group A regs are all recommended for the most strenuous duty. That group includes both the 4 and the 5-port ScubaPro Mark Vs. So, the port orientation does not have enough of a bad effect to move the reg from Group A to Group B.

 

[John C. Ratliff]

so at what point do you deem those values relevant and how does that argument apply to the second stage swivel?

Those values are relevant as they show how a 90 degree turn can influence air flow. But, they 90 degree turn is into a chamber, rather than more restricted in a hose. I would expect the change to be greater in a hose (the 90-degree elbow) than in the chamber because of the restrictions. It's like having a mass of people go down a hallway at full tilt, running, and then having to turn 90 degrees into another hallway. There will be more congestion than if that mass of people were released into a room and have to find an opening at 90 degrees to the entrance hallway. In order for this analogy to actually depict what happens, the hallways and room would need to already be packed with people, and at the end an opening allows the people to start running, creating a space for other people to run, until the whole thing starts to move. In the hallway with the 90 degree turn, when the packed people run up against the wall, some will turn left and some right, and those turning against the opening will have a harder time getting back through (the hallway rather than the room).

I don't think anything over 40lpm/1.4cfm is really relevant, and anything deeper than 132 really isn't relevant since those are outside of the scope of recreational diving.

Well, I'm not so sure of that. Yes, they are probably outside the "normal" sport diving criterion, but, and this is a big "BUT," when you need it, you really need it. We have reports of divers caught in down-currents. We have divers who must lift a heavy object to the surface, or rescue a diver (part of sport diving).

The pressure drop graphs at that range you chose not to upload, and that has a roughly 25psi ip drop for the 5 port, and 30psi drop for the 4 port. Hardly significant in the scope of work of breathing as shown by the WoB being between .1 and .14 for that test cycle. Much of that can largely be given to the cycle time of the regulator which if you breathed at that rate for any length of time *more than about 30 seconds* would cause you to pass out.

Here are a couple of my air consumption rate calculations:

Date: 6-19-2011
Surface Air Consumption Rate:

Used twin 42 cubic foot tanks (PJ tanks), for a total of 84 ft3@2100 psig. Started at 1700 psig. 1700psi /2100psi = 0.81 x 84 ft3 = 68 ft3 available. 700psi /2100psi = 0.33 x 84 ft3 = 28 cubic feet still in the tanks at the end of the dive. 68 ft3 – 28 ft3 = 40 cubic feet used in 22 minutes. 40 ft3 / 22 minutes = 1.8 cubic feet per minute used.

Date: 6-11-2011
Surface Air Consumption Rate (SACR):

Used twin 45 cubic foot tanks, for a total of 90 ft3@1800 psig. Started at 1400 psig. 1400psi /1800psi = 0.78 x 90 ft3 = 70 ft3 available. 300psi /1400psi = 0.21 x 70 ft3 = 15 cubic feet still in the tanks at the end of the dive. 70 ft3 – 15 ft3 = 55 cubic feet used in 52 minutes. 55 ft3 / 52 minutes = 1.06 cubic feet per minute used.

Both of those dives were in the Clackamas River at about 25 feet max depth. But I have had more rigorous dives, where I tested fins and swimming techniques, and spent most of the dive swimming against the current, emptying a single 72 in less than a half an hour. I didn't pass out either. Here's a YouTube video I produced of two of my dives last spring:
You will notice that my breathing rate is about 20 breaths per minute, and I have a six liter vital capacity. I imagine I'm breathing between 4 and 5 liters per breath. So that's between 80 and 100 liters per minute, or 2.8 to 3.5 cfm. You only pass out if the regulator is not giving you enough air! A surface air consumption rate is just that, a rate over time. There is also an instantaneous rate, which can be several times higher than the averaged surface air consumption rate.

So again, how does that chart apply to recreational diving? You posted values for 62.5 and 75 rmv's, can you maintain a SAC rate of 2.5cfm for any duration of time? I highly doubt it.

Yes, and have when I test underwater swimming techniques against a 2 know current. I have done that, at age 71, for over 20 minutes.

Do you regularly violate the accepted max depths of recreational diving at 132 where the gas density starts to cause significant variance between the two? I certainly hope not.

No, not in recent decades.

Since 40 lpm or 1.4cfm is really an elevated SAC rate, do you feel that the difference between a WoB of 0.08 and 0.10 is significant? If so, why?

Yes, because you can get into those situations without being deep. This work of breathing is expressed in kilograms x meters per liter of air breathed. If you'll look at the NEDU document below, on pages 4-6 and 4-7 you'll see that regulators which "exceeded limits" were involved in shallow water fatalities.
http://archive.rubicon-foundation.o...0662/NEDU_TM_15-01_7_July_2015.pdf?sequence=1

How do you know that the second stage elbows yield a similar net effect that is measurable and meaningful within the scope of recreational diving?

Well, it's intuitive that any 90 degree turn, especially in a restricted space, will produce turbulence. As stated above, the turbulence inside the 90-degree elbow is probably greater than inside the first stage of Scubapro's piston stage. But we would actually need to measure this to get an accurate reading on what it does to the interstage pressure under high demand. You don't need to be at extreme depth to have very high exertion rates. All that needs to happen is some emergency, or some unforeseen event (catching a boat in rough water comes to mind) to require a lot from a regulator.

SeaRat

PS, I had to take off the attribution quotes to make this post work. My apologies. I was quoting "tbone 1004."

 

[tbone1004]

@John C. Ratliff you forgot to factor in average depth
yes on the first one you are pulling 1.8cfm, but you are doing it at 25ft or 1.73 ata, which has your actual RMV at somewhere around 1.04cfm when adjusted for depth. 1.04cfm or around 30lpm. Still well under the 40lpm consumption rates that is recommended for "working" dives

The USN says that "heavy work" is about 40lpm to 55lpm, equivalent to running a sustained 7-8 minute mile. That's a LOT. They claim that
They describe "severe work" as 55-100lpm which is comparable to running uphill

Again, in what world are you anticipating working at that rate for any length of time at depth *you should be on helium if doing that below 100ft*, and how much is the elbow going to matter? Show me ANSTI graphs proving it vs. saying that it's "intuitive" of course there will be turbulence and pressure loss associated, I'm still questioning whether you truly believe it matters because it is showing a fairly negligible difference in WoB at even what is considered "heavy" workloads, certainly not something you'll be sustaining

 

[John C. Ratliff]

@John C. Ratliff you forgot to factor in average depth
yes on the first one you are pulling 1.8cfm, but you are doing it at 25ft or 1.73 ata, which has your actual RMV at somewhere around 1.04cfm when adjusted for depth. 1.04cfm or around 30lpm. Still well under the 40lpm consumption rates that is recommended for "working" dives

The USN says that "heavy work" is about 40lpm to 55lpm, equivalent to running a sustained 7-8 minute mile. That's a LOT. They claim that
They describe "severe work" as 55-100lpm which is comparable to running uphill

Again, in what world are you anticipating working at that rate for any length of time at depth *you should be on helium if doing that below 100ft*, and how much is the elbow going to matter? Show me ANSTI graphs proving it vs. saying that it's "intuitive" of course there will be turbulence and pressure loss associated, I'm still questioning whether you truly believe it matters because it is showing a fairly negligible difference in WoB at even what is considered "heavy" workloads, certainly not something you'll be sustaining

I don't need to show you these graphs, as I don't use the 90-degree elbow. How about you show me that my intuition is incorrect, that the NEDU graphs on 4-port verses 5-port first stages (Scubapro) are not relevant, and that these elbows have virtually no effect on regulator breathing performance. This would be a rather easy experiment to do, as all you need to do is hire the ANSTI to conduct their tests on a high performance regulator with and without this 90-degree elbow under the conditions you state, and the more severe conditions a diver could get into. (We have lost divers in sport diving conditions to down-current problems, so this would be useful information to have tested.) I do not now, and will not, use the 90-degree elbow on any second stage I have. It is you who must "prove" them safe under virtually all conditions, and of course, you won't do that as you are trying to sell these to divers.

SeaRat

 

[tbone1004]

@John C. Ratliff I do not, nor have I ever sold scuba gear, so I have no interest in that and unsure where you thought that came about

I will say that Kirby Morgan uses and sells 90* elbows on their hard hats, many of the most extreme cave and technical divers use them on their regulators and have for many many years with no ill effect.

They have also passed CE testing which means they can't have significant effect on the regulator and are sold by various manufacturers as parts of standard kits that have passed CE testing *62.5RMV at 50m with WoB not to exceed 3.0j/l*, if it passes those tests, it's good enough for me

 

[Akimbo]

I will say that Kirby Morgan uses and sells 90* elbows on their hard hats,

I haven't seen these these ells or understand why you would want on their hats. Are you talking about an ell that goes on the check valve (blue cap in photo) or the bailout valve (pointing to the side, not the front)?

Here's a side view (upside down)