Angle Adapters Restricting Airflow?

[Locus]

My regs are set up with a 90° angle on the primary second stage (hose routed under the arm) and a 110° on my bungeed octo. My LDS guy says divers he knows find that they get less airflow with angle adapters because when the gas is pushed through a tight corner it creates a de facto restriction.

Has anyone found this to be true? Have there been any objective tests that might confirm or debunk this?

 

[scubafanatic]

...sounds like material for a Mythbusters episode.

 

[axxel57]

Don't worry, it's not true.

I did some tests and described them in one SB thread in December 2012 I think, which I cannot find right now.

But I can send you the results per mail if you are interested.

 

[Bob DBF]

I did use a 90*, didn't like the configuration and changed to a 70/20* (which may be a 110 depending on how you look at it). I couldn't detect any difference in breathing down to 130'+ on either, I just didn't like the 90* angle.

Theoretically, there would be a difference, but there is so much available flow to the second stage that is never used, I doubt that it would be noticed, especially at recreational depths. As an example of how much flow is available to the second stage, a low pressure hose rupture will empty an AL 80 in a bit over 80seconds (approx. 57 cuft/min). At 6atm (approx. 200'), SAC 1 cuft/min, you only need to flow 6cuft/min. I'm not working the math for precision as the disparity between what can flow and what is needed will be more a function of the regulator performance than the adapters I have, which are the same inside diameter as the hose fittings.




Bob
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"If you don't like it, go on the internet and complain." Brian Griffin

 

[Nemrod]

The basic answer is no. If the "LDS" has divers who are noticing a difference, there is something not right and it is not the angle adapter. This is similar to the port arguments on the Mk V or the long hose vs short hose. The choke point in the system is at the LP seat to the LP orifice knife edge. At no time would the flow be restricted by the 90/110 degree bend any more than at the knife edge/seat interface. Even when the LP seat is fully raised by the diaphragm lever the gap to the knife edge is very small in area.

Those guy might want to check:

1) A hose that is delaminated and closing under dynamic flow
2) FOD in the hose
3) IP not correct, way to low
4) Lever height adjustment too low. If the seat is not opening to it's design requirement then, yeah, you have a restriction but it ain't at the 90 degree elbow unless the opening through the angle adapter passage is smaller than the area of the maximum opening at the seat and knife edge.

N

 

[buddhasummer]

If you can notice any difference with and without I'll eat my regulator.

 

[flots am]

Has anyone found this to be true? Have there been any objective tests that might confirm or debunk this?

Never tested it with SCUBA, but it's true for air ducts and pipes. Sharp bends introduce resistance.

OTOH, the pressure drop is very small and should be undetectable by the diver unless you're running at extremely high flow rates and depths.

What I would be concerned about is the adapter. It's entirely possible that parts of it aren't the full diameter of the hose and that there is hardware in the air path that creates turbulence and/or restrictions.

It should be easy enough to check out on a flow bench. Just check the maximum flow rate with or without the adapter.

 

[axxel57]

Yes, exact what I did in this thread http://www.scubaboard.com/forums/regulators/441538-regulator-second-stage-hose-swivel.html one year ago........

 

[lindenbruce]

Been using then for some years now and never had a problem yet. I prefer the 70degree adapter myself with the long hose. If you are running a standard 40" or 48" hose a 90degree adapter would be fine as long as you route the hose straight down the front of your BC and under your right arm. Otherwise the hose will be pushing up against your right face cheek and my become irritating. B.

 

[Scared Silly]

There is a theoretical difference in terms of the resistance each time there is a bend in the flow. I will not go into all the theoretical details but instead put in into simpler terms. Many have clothes driers which have a maximum length for hose vent. Each time there is bend one has to reduce the total length.

Read more: Dryer Vent Hose Length Considerations | DoItYourself.com

While it may be important to check local guidelines, there are general guidelines followed by the International Mechanics Code. They state that a straight duct be no longer than 25 feet. In addition, if there is a 45 degree bend, then deduct 2.5 feet from the recommended length, and if there is a 90 degree bend, deduct 5 feet. So, if you have a space that will need two 90 degree bends, then you should have no more than 15’ of dryer duct.

A dryer vent hose is similar to many flow systems like a scuba regulator.