breathing position

[ShoalDiverSA]

My mistake. Thanks for the clarification. I have a Mk20 1st stage.

Cheers,

Andrew

 

[waynne fowler]

MK20 is a great performing reg.. the R380's no POS either... Though your comment about it being "like breathing from a plastic bag" would concern me. If you have any friends that have something like an S600 2nd stage.. throw that on and take if for a spin... this may give you some indication of what to expect from a wonderfully engineered regulator as opposed to simply one that is adequate. Personally I used the R390's and R380's as my alternates... but thats a personal thing.. they are adequate primary's.

 

[ShoalDiverSA]

Thanks for all the pointers.

I went diving this weekend (twice! miracle of miracles). The reg was still very difficult to breathe from (no surprise there as I had not yet taken it in for a checkup). However, I did get an opportunity to "feel" the reg out better. The breathing effort was so bad on the second dive that I switched to my R190 octo. What a wonderful regulator! It is really wasted dangling from my BC. (At least I know that I would be donating my best performing regulator to a buddy in an OOA situation - in a totally non-DIR way, of course ). The downsides of the R190 are jaw fatigue and chin-bashing. But I digress.

Anyway, this mini-drama prompted me to pop into my LDS yesterday to get the problem sorted out. After a lot of to-ing and fro-ing, the tech found that:

a) One of the IP shims was not seated properly and had become "graunched" in the 1st stage. This was replaced - but was not the (only?) cause of the problem as my octo breathed just fine. He first thought there may be a problem with the 1st stage as the IP was too low. How this happened, I don't know - but anyway...

b) The diaphragm on the R380 had imperfections in the structure of the rubber. These looked like dimples and bumps on the surface. Not obvious unless you are looking for them. He replaced the diaphragm with a new one and the reg started breathing very nicely. Note that this was a shop test only. I will have to feed back on the performance in the water when I get a chance.

The 1st and second stages were then adjusted to get the optimal breathing effort from the regs. As he had contacted Scubapro about the issue while looking for the problem, the diaphragm was replaced free of charge(!).

My take on what was happening:

When a negative pressure was drawn behind the diaphragm (by me breathing in), the diaphragm was collapsing in a "non-symmetrical" way due to the blemishes in its structure. As a result, the lever was not being depressed smoothly through its stroke, resulting in varying levels of air being supplied during different stages of breathing. (This was particularly noticeable at low negative pressures (sucking softly) as the diaphragm had not moved much.) As a result, the breathing felt laboured at times, varying between bursts of air and very little air being delivered.

Any thoughts on this being a correct diagnosis of the problem? Is this known to be an issue, or am I clutching at straws? Apparently, SP have come across this before, hence the free swap-out.

Even if the point has been missed regarding the cause of the fault, the replacement of the diaphragm did lead to a marked improvement in the breathing effort and smooth delivery of air through the breathing cycle. By smooth delivery I mean that by changing the amount I was sucking on the reg, the amount of air being delivered changed smoothly through the "normal" stroke of the lever. There were no points where very little to no air was being delivered, or where I got bursts of air (no "sputtering")

I hope that I have given an understandable synopsis of what I experienced with all these words.

Thanks for everyone's input. It is truly appreciated. The amount of knowledge and experience on this forum is amazing and it is wonderful to be able to tap into that resource.

Thanks for your willingness to help!

I must also retract my short, yet unkind, comments about the LDS and the service received there previously. A lot of effort was taken yesterday to find and resolve the problem. I had received less-than-optimal service in the past and expected this to continue. However, they really did a great job and deserve kudos for it.

Cheers,

Andrew

 

[DA Aquamaster]

Thanks for sharing that one - a defective diaphragm is something I will put on the list of things to consider in the future.

 

[John C. Ratliff]

A couple of points of clarification from the above posts are in order:

--The relationship between the diaphragm and the exhaust valve only applies to whether the regulator will "bubble" a bit when in the most desirable setting of about 1/2 inch of water inhalation pressure. It does not apply to whether the regulator will breath "hard," unless the technician who set the interstage pressure did so to keep it from bubbling. This is de-tuning the regulator, and can increase the effort quite a lot.

--The main problem with any single hose regulator when vertical in the water is the difference between the position of the demand valve (second stage, at the mouth), and the center of the lungs. That is what you feel as breathing effort, as it is your lungs which must do the work of moving the air. You can see this illustrated in a very old US Divers publication from Bill Barada titled, Let's Go Diving (U.S. Divers Company, 1962):

http://vintagescuba.proboards2.com/index.cgi?board=instruction&action=display&thread=1071253464

--There are many other problems that can affect breathing.

*Low interstage pressure (caused by the shims in this case).
*Diaphragm which has become hard with age, or is defective (some were molded wrong in the 1970s--the Trieste II, for instance).
*Sintered filter becoming either clogged or rusted.
*Demand levers becoming corroded, and applying fraction to the diaphragm's plate.
*Cracked case which allows the valve to rotate, and the venturi not to function correctly (plastic regulators mainly).
*Setting on the second stage inadvertently left in a "hard" breathing position, for those second stages which can be adjusted in the water.

Any of these can cause problems, but you add several up, and you can get quite a water pressure differential for inhalation effort. For instance, let's say that the regulator was de-tuned so it had 1.25 inches of inhalation effort. It's diaphragm was damaged, which added about 3/4 inches of inhalation effort. We're now at 2 inches to crack the demand valve. If the first stage shims had a problem, which dropped the interstage pressure another 10-15 psi, then perhaps another 0.5 inches of water pressure inhalation effort is added. We're now at 2.5 inches to simply crack the demand valve. This is not unheard of, but then we begin ascending, and look up toward the surface. This act adds about 12 to 14 inches of water pressure that the lungs feel, and it would indeed feel like you were breathing through a straw.

I hope this helps clarify the situation.

SeaRat

 

[rockjock3]

This thread is not too old, so I would like to park my question here...

During my "Darwin Award" dive yesterday, I observed that my R380/Mk20+ combination was breathing much harder in the face up position. We were nearing the end of the dive, and I had about 60 bar in the cylinder. We were about to start the safety stop when a Manta Ray joined us.

I looked up at the Manta and sucked on the reg - almost no air. It felt like I was breathing through a plastic bag. I started coughing and gasping and dropped my head to the head-down position to get air. Is this

• normal;
• on the limit of normal;
• or "get your reg checked now"?

I had the reg serviced at the beginning of this year (about March or so) after a Dive Charter staff member decided to wash it without the dust cap on. I must admit that under normal conditions (face down, full cylinder) it is not the most comfortable reg to breathe. But repeated attempts to get it sorted out by the LDS have proven fairly fruitless.

Any help/pointers would be appreciated.

Cheers,

Andrew

I would have to agree with the others. Definitely get it checked out. It doesn't seem like a huge problem but shouldn't be doing that. I personally use a ScubaPro R390/MK16 and don't notice any difference breathing in any orientation all the way from the surface down to 130fsw. I absolutely love that reg.

 

[TSandM]

Super thread to print out for diagnostic ideas for a poorly performing regulator -- thanks everybody!

 

[ShoalDiverSA]

A couple of points of clarification from the above posts are in order:

...

I hope this helps clarify the situation.

SeaRat

Thanks for the further information - and clarifying that the diaphragm can indeed be a source of this type of problem. Unfortunately, I have not had an opportunity to dive the reg yet, but I will give feedback as soon as I have.

Cheers (and Merry Christmas!),

Andrew