breathing position

[kman]

As a new diver, I have had the opportunity to try several different types of regulators . Aside from normal variation in general ease of breathing, I have noticed that some regulators require slightly more effort in breathing when swimming upside down or looking up.
Is this a normal thing to expect from a regulator and is it a matter of second stage flow adjustment or is it an indication of some other issue with the regulator?
Any thoughts?

 

[Ber Rabbit]

This is normal; I have one regulator that gives you a little water when you breathe it while completely inverted (standing on your head).
Ber :lilbunny:

 

[doole]

My classic Cyklon gives me water every time I look up. They tell me it's something about the design. (Which is why I only take the thing out on Sundays.)

 

[DA Aquamaster]

It's due to what is called "Case Geometry Fault" and is related to the relative locations of the diaphragm and the exhaust valve in the second stage.

Level position:
In a normal swimming position with a second stage of conventional design, the top of the exhaust valve is about a half inch below the center of the exhaust valve, so no air escapes from the valve. Due to the slightly elevated pressure in the case, inhaltion effort is slightly higher than it would be with the second stage out of the water.

Normal swim position:
In this position (looking forward and slightly down) the top of the exhaust valve is essentially even with the center of the diaphragm, the pressures are equal and the reg breathes about like it does out of the water.

Face down position:
In a face down position, the regulator is in a "worst case" position with the exhaust valve being about 1.2 to 1.5 inches higher than the center of the diaphragm. This means the pressure inside the second stage is comparatively lower as air has leaked out the exhaust valve until the pressure in the secodn stage is equal to the pressure at the exhaust valve - about 1.2 to 1.5 inches of water less than the pressure at the level of the diaphragm.

Mechanically, this means the diaphragm is already pushing in on the lever due to the lower pressure inside the case than outside the diaphragm. So the regulator's inhalation effort has to be adjusted sufficiently high to prevent the poppet from opening and causing a slight freeflow in this position. On a non adjustable second stage, this is the limiting factor for inhalation effort and normally limits the regulator to an inhalation effort no lighter than about 1.2 to 1.4 inches of water. However, given that the regulator is adjusted to a point just short of freeflow in this position, this position will give the lowest inhalation effort for the second stage.

Face up position:
In a face up position, the opposite is true with the pressure inside the regulator being relatively higher than the pressure outside the diaphragm. The second stage will be very freeflow resistant and a greater inhaltion effort is required to depress the lever so the reg wil breathe a bit harder.

Upside down:
In this position the highest point of the exhaust valve will be .5 to .7" higher than the center of the diaphragm so the reg will breathe a bit easier than normal. But the excess air leaking out the exhaust valve will allow a small amount of water into the regulator and this will pool at the lowest point in the secodn stage - directly in front of the mouthpiece - so the regulator will breathe fairly wet.

So for a conventionally designed second stage, what you have observed is entirely normal and expected.

The exceptions:
Side exhaust regulators like a couple Oceanic second stages, Posiden second stages and the Dacor Viper have the exhaust valve mounted on the side and most of these designs also have the exhaust valve mounted co-axially in the diaphragm. Coaxailly mounting the exhaust vave in the diaphragm limits the maximum distance that can occur between the upper edge of the ehxaust valve and the center of the diaphragm to to radius of the exhaust valve - in most cases about .5 inches.

Most of these second stages will tend to breath wet if you are on your side with the exhaust valve on the upper side. Most of them will also breathe slightly wet when looking up as there is essentially no bottom of the case for water slipping past the exhaust valve during exhalation to drain into and be expelled on the next exhalation.

Other regulators:
The Dacor Quantum and Scubapro D300, D350 and D400 also use a coaxial exhaust valve. The Dacor Quantum uses it in a fairly conventional case design and gives fairly conventional inhalation performace, just with less differences due to diver position and with much drier breathing than a side exhaust design.

In the D300/350/400 series, however the diaphragm is angled with the bottom toward the diver about 30 degrees. So in addition to the maximum difference between the exhaust valve and the center of diaphragm being reduced to about .5", (and in turn an inhaltion effort that can be reduced to about .6 to .7") the "worst case" postion for the second stage occurs in a position a diver will seldom be in and the "best case" position is the diver's normal swimming position. This makes the D300/35/400 series exceptionally good breathing second stages - in my opinion the best ever produced by any company. (On the X650,which replaced the D400, Scuabpro copied the basic D400 layout, but incorporated a normal exhaust valve which eliminates all the advantages of the angled diaphragm case design.)

 

[kman]

Thanks for the info ! Being a newbie, I had to read it several times. I've printed a copy to refer to later as I plan on taking an equipment course.

 

[DA Aquamaster]

It helps if you use your second stage and rotate it around a bit and observing where the diaphragm and exhaust valve are relative to each other in various orientations.

 

[ShoalDiverSA]

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

 

[DA Aquamaster]

It may be normal but I suspect it does need some adjustment.

A MK 2+ R380 can be tuned to breathe quite well with an inhalation effort of around 1.0 inches of water. However, Scubapro specs call for the R380 to be adjusted with an inhalation effort of 1.2 to 1.8 inches of water.

1.2" is fine, but 1.8" is a little heavy and it gets even heavier at low tank pressures where the intermediate pressure on the MK 2+ falls as much as 20 psi, providing less downstream force to assist in opening the poppet valve. When you add to that the positional problems with looking face up that require another inch of water in inhalation effort, you can have an inhaltion effort upwards of 3.0" of water.

The "felt like I was breathing through a plastic bag" comment suggests you may have another problem. The flow rate of a downstream poppet regulator depends on the orifice size and the working range of the poppet. If the working range is restricted, so is the flow rate. The R190/380/390 second stages are all "dual adjustment" second stages where the tech needs to adjust the orifice but then also needs to adjust the lever height. If the lever is too low, you can't get the valve to fully open and you will not get adequate flow rate. If properly adjusted, the reg will begin delivering air with just slight pressure on the purge cover/button. If you have to push any more than about 1/8" to start air flowing, the lever probably needs to be higher.

My suggestion would be check the lever height, ensure the reg is adjusted to produce an inhalation effort of 1.0 to 1.2" of water and ensure it is in good mechanical condition, has a clean filter, etc. Your shop should return the reg with a test sheet indicating Intermediate Pressure and inhalation effort.

One thing with unbalanced regs like the MK 3, MK 2, MK 200, and MK 2+ that some techs miss is that you need to set the IP with a full tank pressure of 3000 to 3300 psi. and that the IP needs to be at the top of the IP range (145 psi) to ensure that it will still be within range at lower tank pressures (about 120 psi at a 300-500 psi tank pressure.) If the shop uses a scuba tank to supply air to the bench, this is a pain as the tank needs to be topped off to 3000 psi before the proper IP check/adjustment can be made. A well equipped bench will have a valve to adjust air pressure to allow the IP to be checked at high and low extremes in pressure to ensure the IP stays within range.

In a reg like the Mk 2+, sometimes I think well meaning techs assume the IP was right when the reg came, then just put the same number of shims back in the reg and assume the IP will again be correct rather than actually checking it. This can perpetuate an abnormally low IP from service to service.

Another thing to consider is whether the customer dives with 3000 psi tanks, 2400 psi tanks or 2250 psi tanks. If they are diving consistently with low pressure tanks, tuning the second stage at the lower max tank pressure (and resulting lower IP) is needed to get maximum performance out of the second stage.

Any one of those things by itself only causes a small hit in performance, but if you start adding them together, the little hits at up to a significant drop in performance.

If your MK 2+ R380 has an IP of 145 psi at 3000 psi supply pressure, and produces an inhalation effort of 1.0 to 1.2" of water at that 145 psi IP (or at the IP commensurate with the max pressure of your lower pressure tanks if you dive lower pressure tanks) then the reg is fine. If not, it needs to be adjusted to meet those parameters if you are going to get max performance from the regulator.

I started with a Mk 3 High Performance (the 80's equivalent of today's Mk 2+ R190 or MK 2+ R390) and loved it, but having dove higher performance Mk 10 Balanced Adjustables, MK 25 D400's and Mk 17 D400's successively over the last 15 years, I do notice that the Mk 2 R190 or R390 just does not offer the same level of performance. The inhalation effort is not bad, it's just noticeably heavier. So if the reg is working fine and is properly adjusted and it still breathes heavier than you like, then it may be time to consider a higher performance regulator.

 

[ShoalDiverSA]

DA Aquamaster,

Thanks a million for the comprehensive response! I will take my reg to a different tech this time - he actually has gauges for measuring breathing effort. The current shop I use gives you a useful yellow tag on the reg showing what the tech suspected was wrong and the parts used in the repair. The reg is "tested" during the service by the tech sucking on it - no real measurements to talk of, other than the IP.

By the way, when you were talking about the Mk 2+ above, is it the same as the Mk 20+, or would the comments be as valid for either 1st stage?

Thanks!

Andrew

 

[DA Aquamaster]

SP made a MK 2, a Mk 2+ and a MK 20, but no Mk 20+. With the "+" reference, I assumed you had a Mk 2+. The only other "+" was used on the Mk 10+

The MK 20 (and the Mk 10+) is(are) balanced design(s) and all of the above would apply except for the drop in intermediate pressure (as the IP is generally very stable in balanced regulator designs) and the "need to move up to a higher performance reg" comment as performance does not really get any better than a Mk20/Mk 25.