My second stage has a knob-thingy

[Deefstes]

I have a TUSA RS-240 regulator and the second stage has a knob for adjusting the air flow.

I am not overly experienced but I have played around with this knob, turning it all the way in both directions, both on the surface and while submerged and I can honestly say that I don't notice a difference in the ease of breathing.

I'm not experiencing any difficulty at all, I just wanted to see how the knob affects the air flow but, as I say, I can't tell a difference.

I have not dived deeper than 20m yet so I'm not sure if the effects only become apparent at higher ambient pressures or maybe I'm really just not experienced enough to notice the difference.

Any thoughts on this?

Also, if the position of the knob makes no difference to my breathing, will it affect my air consumption if it is turned all the way open? I'm keeping it in the minimum position simply because I can breath comfortably with it in that position and I think that I will use up less air that way. Just curious to know how this knob really works and how it affects my air consumption.

 

[Dive-aholic]

The intermediate pressure is probably high enough that the diver flow control isn't going to change things so you can notice it. On all of my regs that have that control, full open gives a slight free flow and full closed makes it a little harder to inhale. I keep mine fully closed if I'm not breathing them and almost fully open when I am. The more work you have to do to get a breath, the higher your breathing rate, so I would keep it fully open.

 

[TUSA]

The adjustment knob on the S-30 and S-40 are used to increase or decrease your breathing effort. Rotating the knob counter clockwise releaves the spring tension against the low pressure poppet allowing the lever to colapse easier. This makes your inhalation effort easier. Rotating the adjustment knob clockwise puts more tension on the spring, the lever will not colapse as easy. This will make your inhalation effort harder.

 

[Deefstes]

Thanks for the answers and thanks for the explanation of the mechanics TUSA. But, as I said, I have so far been unable to notice any difference in inhallation effort. The regulator breathes perfectly easy, regardless of the position of the knob and regardless of the depth I'm at (up to 20m that is).

I was just curious to know if turning the knob all the way open will adversely affect my air consumption if the breathing effort is all the same. But I think I'll leave it open all the way just in case I have to donate my primary to a panicking diver (or I become panicky myself, heaven forbid). At least then I know the panicky diver will be sure to breath as easily as the regulator can afford.

 

[Dive-aholic]

You can also bring it back to the shop you bought it from and have them adjust the second stage properly.

 

[Couv]

Hello Deefstes,

It could very well be that you just need a little more experience to notice the difference and the only thing you can do about that is to get more diving in. However, it could also be that a small adjustment is required. You can try this cracking pressure test to determine whether the knob is actually making a difference.

First, test it with the regulator hooked up to a tank, air on and the knob all the way in. Partially fill your kitchen sink and immerse the regulator with the mouth piece up. Make a note of how deep you can immerse the regulator until air flows. Do the same with the knob full out. Is there a difference? If not, then I would say an adjustment is in order.

Good luck,


couv