Why would one increase cracking pressure to spec on a primary second stage?

[Wiznutaggie]

Yes. But you're wet. I'm dry and sipping my beer.

Seriously, 0.1" one way or the other is not discernable. Magnehelic is quick with an inline adjuster. You learn pretty quickly which regs tolerate a "hot tune" and which don't.

Nice manometer, by the way!

That's a good point... Next time I'm in my pool though, I'm totally bringing a hex wrench in with me!

Thanks, was able to scrounge it up out of odds and ends laying around my shop.

 

[halocline]

Thank you! I understand now! I'm curious then why using a manometer/magnehelic gauge is the way people set up their regs. Wouldn't a more accurate way of doing it be to submerge the reg in a exhaust valve high position and tweak the spring pad just to the point of stopping freeflow after setting the orifice?

There's nothing at all wrong with setting cracking effort using a bucket of water in the manner that you describe. Although I'm not sure it solves the issue of 'how low can you set the cracking pressure before it free flows in use'

That really is best done by experimentation and experience. There are other factors besides case fault geometry that will have an effect, like venturi forces in the 2nd stage. The manufacturer's recommended cracking effort is a bit of a blunt edge; they assume the reg will not have problems at that spec, but it might not be the best you can get it. I used to try to measure cracking effort, but now I just do it by feel. I have enough experience to know how lightly I can set my regs and have them still work without a problem.

 

[Nemrod]

Generally I prefer regulators without the adjustment knob. I do like the Dive-Predive lever. On matched regulators that I dive as a set which do not have the knob I set the octo or necklaced regulator slight higher than the primary. And generally with such regulators it is not wise to set them at the ragged edge of free flow.

But with regulators that have the adjustment knob you have a little leeway as there is a range available to you. You can shift that range up or down a little to suit your purpose. On a SP 109 set for example I tend to set those to barely hiss as I mentioned earlier. On my wife's Legend I set it per specification, that way no matter where she forgetfully puts it the reg will not free flow on her and will still be plenty responsive to her needs.

James

 

[Subcooled]

why would you ever turn in the spring pad to increase cracking pressure

I know already that you are not an ice diver.

It sucks when your reg starts bubbling or even fully free flowing

 

[Wiznutaggie]

I know already that you are not an ice diver.

It sucks when your reg starts bubbling or even fully free flowing

And I never plan to be! 70 degree water is cold enough in my book.

 

[Hoag]

And I never plan to be! 70 degree water is cold enough in my book.

I like my water on dives to be 80/80/80.
80ft vis
80F temp and
80ft deep.

 

[Jim Lapenta]

The LP seat will also begin to take a set and once the groove starts forming, cracking pressure will drop. Possibly to the point where you really have to dial it back to stop a leak. This puts even more pressure on the seat and over time, will result in excessive wear. Thus shortening the life of the seat.
If you have a cracking effort adjustment knob, make sure to always store the reg with it dialed all the way out (in the easiest breathing position) to take the pressure off of the seat.

 

[Subcooled]

And I never plan to be! 70 degree water is cold enough in my book.

In which case you will never turn in the spring pad to increase cracking pressure

 

[Bigbella]

A percentage of particular cracking pressure settings, may simply be a matter of taste.

Some manufacturer's manuals, which are otherwise as strict as a bevy of Carmelite nuns, when it comes to, say, IP and torque settings, have otherwise let loose with potential cracking pressure settings:

"Some divers like the setting extremely light, and some prefer a higher cracking pressure. Ask your customer. Technically, [the regulator] can be adjusted from 0 mm w.c to > 100 mm w.c.

"The risk for a free flow increases with decreasing cracking pressure. Below 25 mm w.c., in a certain attitude (exhalation diaphragm the shallowest and inhalation diaphragm the deepest), the regulator inhalation valve will stay permanently open, bubbling. Above 40 mm.w.c., the breathing [becomes more of an effort] . . ."

All of my personal gear, is typically set to that far lower end of the spectrum -- below 30 mm w.c.; and my over-pressure full-face masks, are actually designed to lightly free-flow -- so light is that setting . . .

 

[madamimadam]

The LP seat will also begin to take a set and once the groove starts forming, cracking pressure will drop. Possibly to the point where you really have to dial it back to stop a leak. This puts even more pressure on the seat and over time, will result in excessive wear. Thus shortening the life of the seat.
If you have a cracking effort adjustment knob, make sure to always store the reg with it dialed all the way out (in the easiest breathing position) to take the pressure off of the seat.

Is it generally recommended to also (or instead) store a second stage with the diaphragm locked in the depressed position?

Would it be advisable to take either or both of these preventative measures between all inactive periods (for example overnight), or only for periods lasting days, weeks, or months?