Adjustable regs? What's the knob for?

[naplestreasures]

Until now I've dived with regs that have no kind of adjustment knobs.
I'm looking at an Oceanic reg that has a knob on it.......I've seen old Scuba Pro regs with them too so I know this isn't a new thing.
I'm asking what the knob is for?
Does this knob have anything to do with freeflows occuring like I've heard some folks mention?

 

[Cavs42]

if the knob you're talking about is on the second stage, it's to adjust the force required to draw a breath through the reg. this helps to stop your reg from free-flowing at the surface when it is hanging into the water by setting the knob to minimim, and when you're breathing through it, it is set to max to ease breathing.

 

[muddiver]

There are different types of knobs on second stage regulators. Some do nothing more than move a vane in the regulator to assist the flow of air through the regulator body after the valve. Others like on the Kirby Morgan regulator actually adjust the valve pressure aginst the seat and air pressure, thus making the opening of the inlet valve harder or eaisier to compensate for depth and divers breathing effort. You will need to really read the manufacturers information on the regulator and research what they are saying to figure out what you are looking at. I reccomend a truely adjustable regulator if you go that route. Sorry, I am only familur with the Kirby Morgan Superflow regulator and I don't know the others on the market that are truely adjustable.

 

[Luis H]

The first adjustable second stage was introduced by Scubapro in the late 60's. The adjustment in that regulator (and in many still today) is the amount of spring tension behind the second stage demand valve.

Most divers do not mess with this spring tension adjustment during a dive.
This adjustment has several advantages:

• The regulator can be set to breath at its best and if any small leak (free flow) starts developing due to seat break-in, the diver can adjusted without having to take back to a technician.
• Any regulator can be used as an octopus by just turning the spring tension a bit harder to avoid incidental free flows during water entries.
• Actually even the primary regulator can be momentarily adjusted to reduce chance of free flow during entry.
  • There are occasions went max performance is not advantageous, like close to the surface when there is some surge that could trigger the regulator.
  • Etc.
  

As mentioned above, there is at least one more type of adjustment that changes the position of a vane to reduce any venturi effect and try to eliminate free flow during water entry.

Some regulators have both adjustments, and some have them combined, or something like that.

I believe the Oceanic does have both of them in some of there regulators.