Stiff breathing MK25/G250

[Hank49]

I have a G250 on an MK25 that is about two years old now. I always thought it was a little stiff breathing. I recently bought a new one for my wife, exactly the same, and hers definitley breaths easier. If you breath in hard on mine, it seems to kick into a second gear and the air flows. Again, it's not bad but....I adjusted the little screw inside where you disconnect the hose from the second stage and set it just about 1/8 turn before free flow. No help.
I thought maybe it was the first stage intermediate pressure but changed to my Atomic B1 second on the same MK25 and it breaths really easy. My friend said I just am unlucky and got a "Monday" product with the G250, meaning someone hungover put it together I guess. Any suggestions?

 

[do it easy]

I'm not that familiar with SP, but it sounds like a cracking pressure/lever adjustment. I think that second gear you described is the venturi effect kicking in- once the air flows, it creates a vacuum that sucks the diaphragm down deeper to reduce the breathing effort.

 

[halocline]

I'm certain it's just out of adjustment. I have a feeling, no proof, that there is a far bigger difference between the abilities of the reg techs working at various shops than there is between the inherent performance of all the major companies' high end regs.

If you can find the right tech, your reg will breathe exceptionally well, as the MK25 G250 is a famously easy breather.

 

[Hank49]

I'm not that familiar with SP, but it sounds like a cracking pressure/lever adjustment. I think that second gear you described is the venturi effect kicking in- once the air flows, it creates a vacuum that sucks the diaphragm down deeper to reduce the breathing effort.

Or maybe the adjustment on that is not pushing the popette open enough, resulting in the stiffness noticed more when breathing slow and high flow when I suck hard on it? I opened it and greased to top of the lever and the underside of the diaphram but was a little hisitant to tear it apart....:11: It IS working at this point....

 

[do it easy]

You could check the cracking pressure between your reg and your wife's. Find a few inches of water, hook up the regs to a tank, and slowly dip them into the water, with the diaphragm down/mouthpiece up. The water will put pressure on the diaphragm and open the valve. Note the water level when the reg starts to freeflow. I think with most high perfomance regs, it will be about 1"-1.5" above the diaphragm.

If the cracking pressures are roughly the same, then it's something else, but it would be an easy and non-destructive test.

 

[ToddK]

Are both regs really G250s, or are they G250HPs? If they are both the same, I'd recommend pulling off the covers of both, and looking at the lever heights to see if you observe a difference in lever heights, or any bending on your lever. I'd also advise checking with Awap or DA_Aquamaster. -Todd.

 

[redacted]

Or maybe the adjustment on that is not pushing the popette open enough, resulting in the stiffness noticed more when breathing slow and high flow when I suck hard on it? I opened it and greased to top of the lever and the underside of the diaphram but was a little hisitant to tear it apart....:11: It IS working at this point....

It does not sound to me like a simple adjustment problem. It sounds like the poppet is not responding smoothly to the lever motion. You might try opening the cover and working the lever by hand very slowly to see if you can feel any odd resistance or hear any jumps in air flow. You could also try some parts swapping with your wife's reg, starting simple with the diaphram and the cover. I'd be looking hard for a small defect in the lever, its fulcrum in the barrel, the poppet, or even the barrel itself. This really sounds like a tough one that may be better handled by a really good tech. Why don't you PM DA Aquamaster ande see if he is interested.

BTW, I suspect that grease on the le4ver and diaphram may just collect dirt and produce more discontinuity in the breathing.

Also, an 1/8 of a turn may be a bit high on cracking pressure. I try to get within 1/12 of a turn of a slight leak. If you get a little too close, you can control it with the adjustment knob if necessary or readjust a little.

 

[DA Aquamaster]

Awap is on the money that 1/12 of a turn inward from the freeflow point is about the max you want to go and expect good performance. With a new seat the "12 to 1" adjustment does a good job of anticipating where it will need to be once the seat breaks in and develops a seating groove.

However on a seat that is already broken in, you can adjust it right down to just barely past the point where it freeflows. In that case 1/8" having the orifice be 1/8 turn to far in could result in a noticeable increase in inhalation resistance.

I have noted the rare G250 with bent tabs on the lever. This can increase the resitance needed to move the lever and in some extreme cases can even cause the poppet to jump past the lever and stop delivering air at all (I have encountered this once in 20 years).

I have also on rare occasions found poppets that just do not agree with the lever being used - probably a case of each being on extreme and incompatible ends of the tolerance range. Changing the poppet and/or the lever usually resolves the problem.

The other possibility is that the spring being used in the second stage is just a bit too stiff and will not allow the normally low levels of performance that can be obtained from what is otherwise an excellent design.

A combination of one or more of the three is what would result in the above mentioned "Monday morning" regulator - but all three are easily fixed with just a little parts swapping. The Monday morning syndrome has however been complicated in recent years as Scubapro and nearly everyone else has felt the need to comply with EU norms that tend to impose totally meaningless performance standards that have the adverse effect of detuning many very good performing regulators. The result is that "acceptable" performance specs like inhalation effort have increased over the last decade. So where in the past a second stage from any number of companies would not have left the factory if it could not produce 1.0" or even sub 1.0" of water inhalation effort, that same second stage may leave the factory with an inhalation effort of 1.4" or 1.6" of water and still be considered to be acceptable. It can perform better, but the reasoning is if it has to be detuned anyway to meet an EU freeflow standard, what is the point?

 

[Hank49]

I'll open it up again tonight and take a look at the lever and as Awap said, see if I feel a "bump" in the depressing motion. I think I'll leave my wife's alone....she's good with a knife. Mine's doable. It's just a bit disappointing. And if I need a lot of air, it's there. Many thanks gentlemen. I'll probably end up taking it to my tech who STILL has my MK20 with the weird leak. He's good but, this is Belize.....

 

[wjefferis]

I have a G250 on an MK25 that is about two years old now. I always thought it was a little stiff breathing. I recently bought a new one for my wife, exactly the same, and hers definitley breaths easier. If you breath in hard on mine, it seems to kick into a second gear and the air flows. Again, it's not bad but....I adjusted the little screw inside where you disconnect the hose from the second stage and set it just about 1/8 turn before free flow. No help.
I thought maybe it was the first stage intermediate pressure but changed to my Atomic B1 second on the same MK25 and it breaths really easy. My friend said I just am unlucky and got a "Monday" product with the G250, meaning someone hungover put it together I guess. Any suggestions?

Just bring you reg in to your LDS or ant authorized ScubaPro dealer and they should be able to tune your reg in to that sweet spot. I have a MK25/S600 and love it.