SP 109 vs (balanced) 250, my experience

[Aloha Joe]

I rebuilt and tuned a 109 and a 250 at the same time with as similar cracking pressure as I could get . My experience has been that the 250 breathes ‘smoother’ - the flow is more linear and easy to control, whereas the 109 will easily force air in my lungs if I’m not being deliberate. I figured it’s because of the air balance, and this seems to be supported by the author in Regulator Savvy (air balancing relieves the duty of the spring to fight IP, therefore a lighter spring is used and hence easier breathing).

I’ve read several times on this forum that there is almost no perceivable difference between balanced and unbalanced regs, so I’m trying to figure out of it’s a tuning issue, or if I should upgrade my 109 to a balanced adjustable.

 

[lexvil]

It’s probably tuning, I can get a 250 to air inject easily enough most of the time and the viva helps a little with free flow. The 109 breathes great but the balance adj makes it a better reg. In my opinion.

 

[tbone1004]

@Aloha Joe there are some pretty substantial case upgrades with the 250 to smooth out the flow so you may also be experiencing some of that

 

[reefrat]

Biggest difference I notice in perceived WOB between the 109/156 and later SP second stages is the smaller exhaust valve of the 109 is slightly more restrictive on exhalation, not a biggie but side by side you can feel the difference.

 

[Aloha Joe]

Thanks everyone. Honestly my gut feel was telling me it had something to do with the lever, but I went back and read Regulator Savvy and the author quite frequently mentions the reduced WOB due to balance chamber, so that kind of redirected my thinking.

My 109 is updated with a dura poppet, and the 250 is an older metal-barrel model updated to poppet with removable seat. So it seems that a difference in lever/poppet/airflow interaction is also plausible.

I have another 250 I was going to setup as a spare. I want to look into the possibility of using parts of it to update one of my 109s to see if I can more closely match the performance of my daily use 250. Granted there are still case and exhaust valve differences, but after reading so many acclaims of the 109 I'm led to believe mine could be better.

 

[halocline]

I have fiddled with dozens of 109s over the years and several G250/G200Bs. I do notice a difference in smoothness with the balanced poppet on the 109. The duro poppet uses a much heavier spring to offset the downstream air pressure. As I'm sure you realize, you're pushing against that spring to initiate breathing. The balanced poppet uses a much lighter spring and IP (in the balance chamber) to offset the downstream force. When you initiate breathing, IP drops several PSI. This means the pressure in the balance chamber also drops, essentially lessening the 'spring' force against IP while air is moving. This makes it smoother. Replacing the small spring with a new (G250) spring seems to help quite a bit too. Those springs wear out and get unpredictable. We can't get new springs for the duro poppet; maybe if we could that would improve its performance.

A really big issue with the 109 is the lever. I have had many of these regulators initially breathe with a 'hitch' as the feet of the lever do not move smoothly. I have found that the curly feet lever (that's the newest version that typically you find on the G250) makes a really big difference on most of the 109s I've had. Occasionally I find one that, for whatever unknown reason, works better with the older levers. There's a big thread about these levers if you search for it.

When I get a 109 correctly set up with the right lever, a new spring, and the s-wing poppet, to me they breathe better than the G250s. I think there's a smoothness in the metal case, maybe because it has more mass, maybe because it has a little less venturi assist. This will never be reflected in WOB numbers.

 

[AfterDark]

Halocline I've got 3 of 4 of my 109's set up the same way (156 balanced 2nd stage) for the same reasons. The 4th is an octo.

 

[rhwestfall]

My first reg was a $25 garage sale 109/MK-5 (maybe a Mk10), and after about 4 or 5 years, got the balanced upgrade installed in it (early 90's). Been diving the 156 for 25+ years. Great regs.

There is a reason I have stockpiled a bunch of them away....

 

[rockinrebel]

How would these compare to the G260?

 

[rhwestfall]

if properly tuned, I'd speculate that only a breathing machine would be able to detect the difference....

I don't have a G260 as I never saw a reason to get one. I have 15-20 metal cased 109/156, maybe close to a dozen G250, and 4 G250v seconds (plus a couple G200B seconds)...

yeah, it is an illness...