Question 2nd Stage Regulator Tuning, noticeable difference in breathing effort of 2 identical regs

[BackstageDiver]

I've realized recently that my 2nd stage requires more effort to inhale than other 2nd stages, even of identical models. My octopus backup is easier to inhale. And I recently picked up an identical model to mine for my girlfriend who just got into the sport. Even being the same model, hers is easier to inhale as well.

We both have Dive Rite RG2010 2nds. I rebuilt both myself with the Dive Rite service kits, both the exact same way. Both were adjusted using an inline adjustment tool to be right on the edge of freeflowing. But still hers is easier to breathe than mine.

What adjustments did I maybe overlook, or what else could cause such a difference in breathing effort?

 

[Nemrod]

Do those have the micro adjust in addition to the orifice/lever height adjustment? Is the IP the same for both sets? Is the dive/pre-dive lever set correctly?

N

 

[BackstageDiver]

Do those have the micro adjust in addition to the orifice/lever height adjustment? Is the IP the same for both sets? Is the dive/pre-dive lever set correctly?

N

Yes, they have external adjustment knob as well. IP was set identically (I also rebuilt the matching DR RH1208 1st stages). Dive levers set the same as well

 

[rhwestfall]

Yes, they have external adjustment knob as well

Not what he is asking... There is a design where there is a internal mechanism on the balance chamber side that you use to set cracking effort. With this, the orifice is just setting lever height. This is not the external adjustment knob we see on many regulators....

Now, as to your issue, is it possible the levers are at different heights? You have to realize we are talking about levers, and the mechanical advantage, even if just a micro-tolerance different, can have a difference in performance (cracking effort). Could be a bent lever, could be bent lever tabs, bent lever feet, a worn/corroded air tube, could be a spring issue (operating in a slightly different working range), etc.

Have you used a magnehelic to actual measure cracking efforts?

 

[BackstageDiver]

Not what he is asking... There is a design where there is a internal mechanism on the balance chamber side that you use to set cracking effort. With this, the orifice is just setting lever height. This is not the external adjustment knob we see on many regulators....

Ah my mistake. In that case, no they do not have a fine adjustment. Just the orifice and the external knob

Now, as to your issue, is it possible the levers are at different heights? You have to realize we are talking about levers, and the mechanical advantage, even if just a micro-tolerance different, can have a difference in performance (cracking effort). Could be a bent lever, could be bent lever tabs, bent lever feet, a worn/corroded air tube, could be a spring issue (operating in a slightly different working range), etc.

All certainly possible. I never noticed any difference when rebuilding them, but I wasn't looking to compare them at the time. Next time I'm at the bench, maybe I'll have a look

Have you used a magnehelic to actual measure cracking efforts?

Negative, I do not have one. Perhaps I could get one, but it's a bit more expensive than I'd like for something I'll use very rarely, especially since my regs don't seem to have fine adjustment anyway. -Edit: I just found a digital one under $100, maybe I can grab that

 

[rhwestfall]

Perhaps I could get one, but it's a bit more expensive than I'd like for something I'll use very rarely, especially since my regs don't seem to have fine adjustment anyway.

There are threads buried deep here on SB that show you how to make one with tubing, a ruler, and colored water.... very inexpensive, and very valuable...

 

[rhwestfall]

There are even manometers on Amazon that are used in HVAC that could be implemented quite cheaply....

 

[runsongas]

check the springs are the same length still (part RG1407). if one has been compressed more over time, you can try to carefully pull it back and reset the length. or see if DGX can sell you a new one.

 

[inka]

There are threads buried deep here on SB that show you how to make one with tubing, a ruler, and colored water.... very inexpensive, and very valuable...

this picture of tubing is from a member of scubaboard

 

[halocline]

If you can feel a noticeable difference in cracking effort, enough so that it bothers you, then something is wrong for sure. I'm not familiar with the 2nd stage you're working on, but it sounds like it's similar to one of the older G250s, a barrel poppet design, with a single adjustment at the orifice, and a user adjustment at the other end. I'm also assuming you are starting with the user knob turned all the way out, and you said you used an inline tool to get them on the edge of free flow. So assuming all that is true, the most likely scenario IMO is the lever height, check to make sure they are the same. Just take the diaphragm off and look closely at them from side view, you can use a straight edge and a small ruler to measure the height. Check to make sure the diaphragms are identical. If those things check out, look for any nicks or problems in the orifice edge. Those have to be nice and clean to seal easily against the seat. While you're at it, look closely at the seats for any imperfections.

Then if all that is good, switch the springs and see what that does. On the older G250s et al, I've had good luck improving the tune-ability by replacing the aging springs that are installed when I get them.

Hope this helps.