Mares MR12 with Proton Nitrox hard breathing

Hello

have MR12 Proton reg, always used with air, serviced yearly, its 2 years old. Got nitrox cert this past weekend and while diving with it had a hard time breathing from it towards the end of the dive. Had about 900 PSI left, was at 60ft. I had to suck in a little harder than normal to the point where I noticed it.

Buddy has MR12 Rebel and he said the same thing after we got back on board. I wouldn't of thought much of it except for he had the same experience. Second dive on nitrox (32%) was 30 ft reef and never got below 1200 PSI, did not experience the difficulty.

Can anyone shed some light on this ? I can't imagine this is a normal thing.
thanks
fs.

Harley,
I must be honest I've not heard of this before. Did you and your buddy have the regs serviced prior this last dive? If so maybe the tech didn't have it tuned as well as it could be? Maybe someone else here on the board has an explanation, but I feel like I would have heard of this scenario before. We've got a lot of nitrox divers using our regulators. Try taking it back to your lds and have them bench test it to assure it is tuned properly.

Zak

Are you sure that your tank valve was turned on all the way?

Zak,
My reg was serviced in June and had 6 dives in it since then, did 2 nitrox dives and then 2 air dives, the only problem was the one 66ft nitrox dive, all others went well. My buddys reg is past due service by a few months. My air was up all the way, definitely.

I'll check next time, I should be doing a 50+ ft dive and see how it goes.
thanks

Hello;

I also have an MR 12 Proton and last week I took it at 91 feet with NITROX 30 for the first time. I did not notice any difference in the breathing. May be this info helps.

My son and I both have the mr12 proton and dove this past summer to 102' on nitrox 32. We didn't have any problems at, they did as well on nitrox as air.

My thoughts are that there is nothing about the regulator design that should be causing the problem, especially on an intermittent basis.

The leading suspect in my opinion would be a valve that was only partially open. It may have delivered enough air at high tank pressures to meet your needs without an excessive drop in intermediate pressure. However as the tank pressure reached a certain point, the flow rate may not have been adequate through the restriction posed by the partially closed valve that the intermediate pressure in the first stage fell on inhalation to the point that the inhalation effort at the second stage greatly increased.

Personally, despite the best efforts of DM's and boat staff, no one touches my valves betwene the last time I check them and the time I get in the water. There has been more than one DM or boat monkey who got themselves confused about the lefty loosey righty tighty thing and fixed what they thought was a closed valve and left it 1/4 turn open.

The other less likely suspect was contamination in the tank that partially blocked the filter - although that tends to persist in your regulator until the filter is changed. I would give it a visual inspection anyway and see if you not any rust (reddish brown), corrosion (greenish yellow or white) or carbon (dark grey or black) on it.