venturi off while diving

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FinnMom

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A fellow recently claimed vast credentials for himself, then told me there is something wrong and unsafe about diving with the venturi off/disabled. I never saw any harm in leaving it off if I found breathing quite easy enough w/o it. Is there any truth to the critic's claims?
 
WHAT! You had it off.....and you didn't DIE?! :rolleyes:

It's a little flap of plastic that modifies the airflow characteristics in the reg. Depending on the reg (it's more effective in some regs than others) and the diver, a lot of people wouldn't be able to tell you when it's on or off. The markings are generally so small and poor that's it's impossible to tell without great light and magnification what position it is in. :confused:

I have had it off for whole dives and wondered why the reg felt a little detuned, but blamed it on how I was feeling that day. Didn't really affect the dive at all.
 
The regulator is designed around "work of breathing" with the venturi engaged. If it is certified to EN250 or approved by the USN then it probably doesn't meet that standard with the venturi off. Diving with it turned off simply increases your WOB for no gain.

The reason you have a venturi adjuster is to reduce the risk of freeflow on the surface. A finely tuned regulator with venturi on will easily produce a self-sustaining free flow if it is not in a diver's mouth and the purge is tapped or the diaphragm depressed.

Ironically, the Apex MTX-R is designed for military use and deliberately has no adjustable venturi because divers would deliberately turn it off and then do the dive with the regulator not performing to the required standard. The military, being obliged to ensure that the regulator did meet the standard, asked for the adjuster to be omitted to prevent this.
 
The reg this guy was referring to was an XTX-50. I almost always leave it off because it's easier not to fiddle with it and at normal depths I rarely find any desire to have the reg breath more easily.
Is there anything wrong or unsafe in this?
 
I see nothing wrong. I've got the Hollis DC212's that have both the dive/surface venturi toggle as well as a fine tuning adjustment dial. I keep them both cranked closed to "-" esp. while side mount diving to give it every chance to not free flow. Never noticed a difference in work of breathing even at depth (down to 95').
 
The reg this guy was referring to was an XTX-50. I almost always leave it off because it's easier not to fiddle with it and at normal depths I rarely find any desire to have the reg breath more easily.
Is there anything wrong or unsafe in this?

As already mentionend does the venturi kick in at different 2nd stage models at different flow rates.

There are some notorious strong and vicious venturis as in the R190s and others which kick in only at a quite high Flow rate like 4-5SCFM, all that depending also on the fine adjustment of the 2nd.

My experience with Apeks 2nds is that their venturi tends to kick in relatively late in comparison with other 2nd stage models, even if adjusted to the lighter side of the specs.

Diving with the venturi off in moderate depths is for sure not unsafe, on the other hand as Dive Pro taking care of clients I would like to have the lightest WOB in case of a stress situation which might occur out of a sudden.

I dive always with the venturi open for this reason and, of course, because my Ds have only a Dive/Predive switch.:)
 
I spent the better part of a few dozen dives trying to guess which position my knob was in... The odds of being correct worked out to 50/50. Not convinced it's a significant difference at recreational depths.
Cameron
 
I use Apeks exclusively.
The venturi is always set at + on the primary and deco regs while it is -ve on the alternative air source.
 
https://www.shearwater.com/products/perdix-ai/

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