Uses of the spring adjustment knob

[Divor]

What are the uses of the spring adjustment knob?

I've only found two:

1) with heavy exertion you want less effort breathing
2) in strong currents you want a bit more

Are there any other uses of the spring adjustment knob?

 

[Peter_C]

I would consider my main use that of keeping them from free flowing when not in use, but when in my mouth I open them up so they breathe nice and easy. Both my primary and my bungeed backup have adjustment knobs.

 

[Divor]

Thanks for your answer.

Doesn't the dive/predive venturi control lever serve that purpose?

 

[redacted]

The venturi control does not prevent free flow but does reduce the severity of a freeflow should one occur.

With a cracking pressure adjustment knob, you can be more aggressive when tuning the reg for top performance and control any small problem that may occur as the seat takes a set.

 

[Divor]

With 'cracking', do you mean an adjustment knob that has a ratchet?

 

[redacted]

The term "cracking pressure" refers to the amount of force required to pull the LP seat away from the orifice and start gas flowing through the 2nd stage. That pressure is regulated by the string pushing the LP seat into the orifice.

 

[Divor]

Thanks for clearing that up.

 

[fppf]

The "venturi" switch does help prevent inadvertent free flows when the reg is not in your mouth. It does this by making a small restriction and causing a small pressure increase in the body of the regulator when it starts to flow. This pressure increase will close the seat.

With no restriction most regualtors are designed to induce a pressure drop in the body, which causes the seat to open more and then free flow. But, this same effect helps reduce breathing effort when the regulator is in use and the exhale keeps the reg from free flowing.

That is why they allow you to turn the "venturi" switch on and off.

 

[herman]

What are the uses of the spring adjustment knob?

I've only found two:

1) with heavy exertion you want less effort breathing
2) in strong currents you want a bit more

Are there any other uses of the spring adjustment knob?

I see you are posting a lot of questions of reg design- great thing IMO- so I have a suggestion for you. Order this book and read it- "Regulator Savvy" by Peter Wolfinger, I have you a link below. It will answer the questions you have and the ones that will come later once you learn more. The book is well worth the cost and if I had to bet darn near everyone who has answered you has a copy. It is pretty much the bible for those of us who really want to know how these things work.
Scuba Tools - Regulator Savvy Book

 

[Divor]

Thanks so much for the pointer.