Venturi lever and adjustment knob

[MikadoWu]

Hello All,

Since I started diving, I have owned 6 Atomic regulators sets and 1 2nd stage DGX. With the Atomic I have always turned the adjustment knob opened to full and left it alone. Speaking with LDS and other divers, this seem to be the general way of using the Atomic Regulators.

Yesterday, my dive buddy gave me a new set of HOG D3 Regulators. The HOGS have both an adjustment knob and a Venturi lever, according to the YouTube video.

I have read different articles on this, and some information seems to conflict.. Anyone mind giving me a brief, and best practice setup?

 

[aviator8]

Venturi is set pulled toward you for dive, and away for predive or for octo. Predive (away) reduces freeflow potential on a reg tuned to breath very easy. Then adjust the adjustment knob to your breathing comfort.

 

[shurite7]

On the surface the venturi, positioned in min / - / pre-dive (depending on how the manufacturer labels it), is used to prevent unintentional free flow when out of the water by creating turbulance inside the second stage to prevent the diaphragm from staying sucked in. If the venturi is set in the above position and you press the purge without any back bressure on the mouth piece it will free flow due to a vacuum behind the diaphragm; Alec Pierce has a nice video on youtube regarding this. When in the water the venturi is turned to max / + / dive since the reg is in your mouth to help give a smoother flow of air into your mouth. It does not change how much air comes out of the second stage.

The inhalation adjustment knob is used to create tension or lesson tension on the spring, thus reducing how much air comes out the second stage. In most cases the knob is turned all the way out to allow ease of breathing. In some cases, such as diving against currents (a river for example) or in cold water, the adjustment knob can be turned in creating tension on the spring requiring a little more effort to breathe. Some people are in the school of thought that if you turn the knob in you'll get less air, thus conserving your gas supply. I'm not in that school of thought after trying it out when I lived in the tropics. One should be able to breathe easily and comfortably, and not have to pull on the reg to get gas to come out of the second stage.

 

[Lorenzoid]

The adjustment knob relates to cracking pressure--the effort you have to exert when you inhale for the demand valve to just begin to open. You can adjust it to make it harder to open or easier to open. Adjust it so that it opens as easily as possible without free-flowing. Remember, pressing the purge button also causes the valve to open. When facing into a current, the water may exert some force on the purge button, helping it to open even when you're not inhaling, which is undesirable. If that happens, then you might want to back off the adjustment knob so it doesn't open until you inhale. In summary, if it's bubbling when it shouldn't, then dial it back. Otherwise, leave it fully in the position that requires the least inhalation effort.

The venturi lever has two positions: a position in which the air flow between the mouthpiece and the diaphragm that acts on the valve lever is smooth, and a position in which the air flow is made less smooth by placing a sort of baffle in the path. A smooth air flow means that, once your inhalation has cracked open the valve, the resulting air flow helps keep the valve open without you having to continue to inhale so hard. In other words, you get a bit of an "assist," presumably thanks to the Venturi effect. A less smooth air flow means that you have to continue to inhale just as hard to continue to keep the valve open. That position inhibits free-flows. Some regulator manufacturers refer to that position as a "pre-dive" position, the idea being that having the lever in that position when you first jump in the water can help avoid the free-flows that sometimes occur before you descend. Unless you're having free-flows, there is no reason to have the lever in that position.

 

[buddhasummer]

Great answers given above.

 

[MikadoWu]

. Some people are in the school of thought that if you turn the knob in you'll get less air, thus conserving your gas supply. I'm not in that school of thought after trying it out when I lived in the tropics. One should be able to breathe easily and comfortably, and not have to pull on the reg to get gas to come out of the second stage.

This is the school of thought I have been trained with in Florida.

Thank you both for the replies and explanations.

 

[AndyNagy45]

Why is it some regulator designs can incorporate the Venturi and the airflow into one adjustment knob.