Double hoses and trimix?

[Akimbo]

Pete,

I was wondering why that plug was in the cross-over manifold. Thanks,

SeaRat

The plug was there because it was much easier to drill the hole perpendicular to the inlet tubes. I have one of those doubles adapters with and without the plug and the US Divers unit with the plug has a much larger hole than the one with a diagonal hole drilled at the yoke connection. The plugged doubles adapters were on the market for years before USD came out with the Delta Triples.

The only reason I know anything about this esoteric subject is because I dove a USD Delta Triples unit in the pool at Al Gidding's Bamboo Reef in San Rafael and later tried building one. I ended up with a separate single-hose regulator on the third tank instead. I was 17 and enamored anything to do with long duration and deep dives.

I learned two important life's lessons from this exercise. Long dives are limited more by keeping the diver warm than supplying gas and there is a limit to how much crap a diver can carry and actually get anything done.

 

[Akimbo]

Here are several comments related to this discussion. To the basic question, US Navy Sea Lab I and II crews used HeO2 (not trimix) on Scuba with double hoses, mostly for crew transits and quick support jumps. They had very long lists of failures on both of these projects, but Scuba regulators were not listed on any of the reports I saw. There was a period where I often had weekend duty at the Submarine Development Group HQ in San Diego with almost nothing to do. I spend most of my time in the tech library reading through unclassified reports and looking at photos from the Sea Lab programs and the Trieste missions on the Thresher and Scorpion.

Anomalies occur with all regulators; and all other valves for that matter. Many valves will leak due to the lower density of helium. Weird harmonics can (rarely) occur as gas density changes due to compression and mixes. I have seen some cases where regulator performance will improve at greater depths —the test medium was always HeO2 in this case but likely would occur with others.

I remember reading about an incident where a semi-closed circuit rebreather was sent down in a chamber through an equipment lock. Like many units of the day, they had a manual valve that could be closed on the mouthpiece. The tanks were off and the crew forgot to open the mouthpiece valve before closing the door. Photos showed part of the inhalation breathing bag was forced up into the corrugated supply hose. I "assume" that the hose did not collapse. Mushroom check valves would have prevented the same thing happening to the exhalation bag.

My "guess" is these bags are a whole lot tougher than human lungs so I doubt that hose collapse from pressure differential would ever occur… before someone is dead anyway. Hoses were smaller then… more like the diameter of a double-hose regulator than on modern rebreathers.

…With my experiments, there is no noticeable difference with a hose in hose set up until one is in a head down position.......senses make you feel like your breathing a hybrid single/double hose, at least to me...........but head down, the breathing effort is the same as head up........so there is some value however, I'm not sure the expense and effort is warranted............it's easier to teach someone to just roll to their side for extra air head down...........

The practical illustration used in my first dive class was watching the instructor kneeling on the pool bottom (head up position) and taking his double hose mouthpiece out. Raising from chest to above his mouth (and regulator can) illustrated to all of us the differential pressure acting on the regulator diaphragm. By 1962 all double hoses had mushroom check valves on both sides of the mouthpiece where earlier models didn’t always react so predictably.

 

[oldmossback]

The practical illustration used in my first dive class was watching the instructor kneeling on the pool bottom (head up position) and taking his double hose mouthpiece out. Raising from chest to above his mouth (and regulator can) illustrated to all of us the differential pressure acting on the regulator diaphragm. By 1962 all double hoses had mushroom check valves on both sides of the mouthpiece where earlier models didn’t always react so predictably.

I must not be reading your answer correctly........what connecton between what I stated about a Hose in a Hose reg setup and the breathing effort head down, referencing the differentail pressure between the can and the mouthpiece and your statement?

 

[John C. Ratliff]

Mossback,

I read you correctly. The others may not know that you are experimenting with the hose-within-a-hose concept from the first USD single stage double hose regulator, the Overpressure Breathing regulator (predicessor of the Stream Air and Mistral). This was the first venturi regulator for USD, and was very easy-breathing. But it was also problematic for people used to a DA Aqualung--too much air coming past their teeth. Your experiments confirm my observations on the Overpressure Breathing regulator, that it is very sensitive and provides a very good venturi even with extremely long hoses. The originals had very short hoses, and I put long SCBA hoses on mine to connect to the metal mouthpiece with the three drilled hose aimed down the diver's throat. It is a very quiet regulator too.

SeaRat