Venturi adjustment: real benefit?

[HBO MD]

Just a question regarding the value of adjustable venturi : do you really think it is of any value, or merely complicates things?
I ask this as one wishes to minimize work of breathing : period. As such, in a conscious individual, you will determine flow, rate etc. I would imagine that we all merely want minimal work at any given load.
What has been the value of incorporating this feature into regs recently, in your opinion? Is it worth the extra cost of purchase and presumably service?
Just curious.
Thanks.

 

[redacted]

If you do not have a user adjustable cracking effort on an octo, I think a user adjustable venturi is useful to minimize the effects of the occasional freeflow. I prefer the user adjustable cracking effort control to minimize the occurrence of the start of a freeflow rather than just controlling its severity.

For a high performance primary, a user adjustable venturi may be useful to tune away the feeling of gas being being forced into your lungs (positive pressure breathing) if it is uncomfortable.

Finally, a user controlled venturi is a fairly simple reliable device, so having one that a diver rarely if ever uses is still not a major drawback. Most newer higher performance regs come with one whether you want it or not. Its absence generally indicates and entry level 2nd stage. That said, I dive mostly older Scubapro metal 2nds which do not have such a feature. If you really want simplicity and high performance, you need to reach back 20 years or more.

 

[HBO MD]

Thanks awap.
Ironically, I started my dive vacation with a Scubapro X650, where the venturi was optimized. A tank hit it and I returned to my D 400, which lacks the venturi but is very sweet to breathe with. A regrograde step historically, but a fine working device.
I work with mechanical ventilators so I am aware of work of breathing etc. Hence my sense of questioning re the actual benefits of adjustable venturi where "cracking effort" , or triggering a breath is desired to be minimal.
Thanks.

 

[widget]

Yah, I tend to agree with awap, it seems almost all the manufacturers now put these on their mid to high end regs, so it leaves really little choice if thats where you are looking.

My personal feeling is that they are not "that" usefull, anything "user adjustable" in a demand valve generally gets set to the easiest, lightest setting and stays there, which makes its range redundant anyway.

 

[scubafanatic]

...I think you're missing the point of the 'adjustability' feature.....it allows you to achieve the optimum balance between breathing effort and the forces acting/pushing on the 2nd-stage diaphram ...if you've ever done a giant stride off a boat or dock, or swam into a variable current....or swam at different speeds....or needed the ability to tweak the breathing effort based on differences induced by different reg techs...then you should understand the benefits of 'adjustability' by the end user in the field, under real-world conditions.

Karl

 

[halocline]

I returned to my D 400, which lacks the venturi but is very sweet to breathe with. A regrograde step historically, but a fine working device.
I work with mechanical ventilators so I am aware of work of breathing etc. Hence my sense of questioning re the actual benefits of adjustable venturi where "cracking effort" , or triggering a breath is desired to be minimal.
Thanks.

The D400 is kind of a special case (no pun intended). It does have a venturi assist adjustment; it's usually set my the tech and left alone. It's a ring inside the mouthpiece flange that covers up an adjustable amount of the air outlet opening in the aspirator. Honestly I don't know how effective it is, I usually set mine about halfway and leave it. In terms natural breathing, I don't think you're likely to match the D400. The geometry of the case and design of the poppet balancing help deliver air smoothly without much venturi assist.

There are some reg designs that rely heavily on venturi assist and I suspect they are designed in part to achieve very low WOB scores on machines. However, the feeling of air being pushed into your mouth is not my idea of a great reg.

 

[beanojones]

The D400 is kind of a special case (no pun intended). It does have a venturi assist adjustment; it's usually set my the tech and left alone. It's a ring inside the mouthpiece flange that covers up an adjustable amount of the air outlet opening in the aspirator..

I was gonna post this, but he already did. D400s however are a pain in general to work on, and if not properly set up end up not breathing well at all. I know that the ScubaPro warehouse in Hawaii always used the D400 in regulator tech
contests to see who did the best work in the fastest times. And there was always a huge difference in preformance between the winner and the non-winners reg.

Atomic has an interesting design that only adds the venturi effect with depth.

Personally I don't like regs that don't have any sort of venturi effect, in terms of breathing efort. But I understand that the venturi effect is annoying at the surface, where bumping the purge button causes that godawful noise. Or when students toss the reg out and it hits the water (or even if the just leave the mouthpiece facing up, it causes the same noise and/or furious bubbling. IME, the reason that entry level regs do not have venturi effect (for the most part) has more to do with rental gear/student gear considerations than anything else. I know it was the reason that most places did not use the R190 in rental, even if they did use the SP entry level first stage (Mk2) or an eqivalent.

ScubaPro r190s, for instance, that had a venturi effect knob that was adjustable but not indexable, were annoying enough that ScubaPro used to recommend locking the venturi assist adjustment into place with glue for R190s that were to be used in rental fleets. Nowadays most second stages that have venturi knob 'index' the knob so it can be set and then left alone for octopuses or even for primary second stages.

Atomic probably got the idea right in terms of idiot-proofing the venturi assist, as mentioned above, by making it not user adjustable, but simply a function of depth. IIRC, it is wide open by the time you hit 30 feet or so.

 

[fdog]

I have an Atomic B2. I dive it a lot, and use the user adjustment all the time. Honestly I can't imagine diving without the option of adjustment.

I have used quite a few regs that the "user adjustable" knob may as well be a decoration. The Atomic really works.

If it's a lazy dive, or fairly deep, it's cranked to easiest breathing. I can't say that the true WOB is any better, but the lack of cracking effort and smoother inhale characteristics sure make for a more enjoyable dive. The reg becomes "transparent" and I like that.

On other dives, like like high-speed scootering, I will set it to highest breathing effort so it doesn't freeflow as easily. Or teaching dives when it's in and out of my mouth a lot. So, I use all the adjustments on most dives.

Yes, it's worth it, providing it really makes a difference.


All the best, James

 

[Packhorse]

I have steadily worked my way backwards thru the Scubapro range. I started with a S600, then G250 and now only dive 109 BA's. These lack the venturi adjustment of the S600 and G250 but I dont miss it at all. I would miss the cracking pressure adjustment. In fact I wouldnt buy a reg with out it.

 

[HBO MD]

It seems then, that the Atomic's venturi titrates cracking effort to minimize work of breathing with depth.
I understand the above points in relation to work effort, but I guess that's my point: if work of breathing is to be minimized, is manual adjustment/titration really of particular benefit? Why not have it just as the Atomic or SP D400?
Sorry to belabor the point ; just curious....must be the turkey