U.S.D. Single stage two-hose regulators compared by NEDU

[SeaRat]

In doing research on zthe old, Nave aluminum tanks, I ran into this study of U.S. Divers Company's single stage, double hose regulators, the DX Overpressure, the DW Stream Air, and the Mistral. I thought you'd like to see the link.

dspace.rubicon-foundation.org/xmlui/bitstream/handle/123456789/3818/NEDU_59_09.pdf?sequence=1

I will have more comments later.

John

[vance]

Interesting. I am surprised that the old style can/exhaust duckbill mounted on the Mistral lowered its exhaust resistance compared to the DA type duckbill.

[SeaRat]

Jun 29, 2019 11:10:41 GMT -8 vance said:

Interesting. I am surprised that the old style can/exhaust duckbill mounted on the Mistral lowered its exhaust resistance compared to the DA type duckbill.

I have known that for a long time, as I have two regulators with the old-style exhaust. One is the DA Aqualung, and the other is the DX Overpressure Breathing regulator. At one point, to make my Mistral better, I had the DA Aqualung bottom box mounted on it. It has to do both with the diameter of the opening being narrowed by the duckbill, and the shape of the duckbill openings. The original openings were wider that those now. I'll see whether I can rustle up some photos to illustrate this.

John

[SeaRat]

Here's a quote from this study:

5.1.3 Comparing the MISTRAL with the older DW single-stage regulator, (specifically figure 3 with figure 4) it will be noted thatthe inhalation characteristics are superior (due no doubt to the "venturi" action) and the exhalation characteristics are essentially the same....

5.1.4 Comparing the MISTRAL's inhalation characteristics with those of theearlier Model DX, figures M1 and M3 of (2), it will be noted that the resistance isnearly the same. This may have been anticipated as the DX was essentially a venturi action, though by different means. The DX's venturi action, however, was objectionable due to the spray of water in the mouthpiece from the inhalation tube's inner hose. Subjective runs on the MISTRAL are not reported and so no comparison is made.

John

[vance]

What was the spray of water from? I know the intake non-return valve was iffy, but why was water in the intake hose?

[SeaRat]

Jul 1, 2019 16:41:01 GMT -8 vance said:

What was the spray of water from? I know the intake non-return valve was iffy, but why was water in the intake hose?

First, let me talk a bit about the duckbill situation. Here's a photo from a write-up on the duckbills:


You can see the difference between the old and newer style duckbills (the "newer" ones were from the 1950s; keep that in mind). The newer one is standing up in the back on this photo. Note the diminished volume.

Now about the spray in the mouth. It only happens occasionally. Here's the drawing of the hose-within-a-hose concept, the first Venturi for SCUBA.



What is not shown is the metal tube inside the mouthpiece. If water entered this Venturi tube, and the air went out into the mouth, it would come with a spray of water. Realize that today, divers are pretty much used to getting some spray with their Venturi air from single hose second stages at times. But at that time, in the late 1950s, it was entirely new, as the other double hose regulators had very little to no Venturi at all, and the air had to be sucked out of the regulator box.

John