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"W.J. (Bill) Dean (U.K.)." wrote in message ...
Do Drager still manufacture their diluter demand system for aircraft?

I used one of these sets in an ASW20 some 20 years ago. It was a very good set, I understand the design was originally military for the German air force in the 1930s. It was proper aviation equipment for use in unpressurised and unheated aircraft.

It had several safety features.

1./ You could turn on the bottle on the ground, when you wanted oxygen you simply put the mask on and breathe, nothing else to do or adjust.

2./ There was a blinker, and the demand valve made a distinctive noise. In diluter mode if you breathe with the mask on, with the oxygen turned off, then no blink and no noise.

3./ When set to 100% oxygen, if the oxygen is turned off or fails then the mask immediately collapses and you cannot breath - instant warning.

I notice that Mountain High are advertising a mask by Drager for their EDS system, it looks similar to the one I used
http://www.mhoxygen.com/index.phtml?...product_id=406 .

I suspect that the Drager system was as good as any of the ex-military systems up to the altitude where pressure breathing becomes necessary.

W.J. (Bill) Dean (U.K.).
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This is exactly how the diluter demand systems work. The aneroid altimeter in the regulator adjusts the dilution by cockpit air so as to deliver the proper O2 partial pressure to the mask.

Pressure demand systems work like diluter demand systems until some preset altitude such as 37,000 feet above which they automatically begin to deliver O2 under slight pressure . In the pressure demand mode, the pilot must consciously shift his breathing to force air out of the lungs and relax to let the O2 system force oxygen in. This is tiring and it's a big relief to descend below the pressure breathing level.

Masks for the pressure demand systems have an exhaust valve that requires an air pressure of 1 or 2 mm of Hg to open. This makes a pressure demand system and mask a bit harder to breath through below about 15,000 feet. The exhaust valve is slightly more susceptible to icing than a diluter demand mask.

You can use a diluter demand mask with a pressure demand regulator as long as you stay below the altitude at which the regulator shifts to pressure demand. Then the O2 will just be lost overboard as the exhaust valve in the diluter demand mask won't hold the pressure.

The complaint that the military systems are "very uncomfortable to use" comes from civilians unknowingly using pressure demand masks not understanding that the mask exhaust valve is restrictive below 20,000 feet.

The advantage of the latest military regulators is that they use long life components unlike the A-14 that uses natural rubber elastomers that are attacked by O2 and so requires rebuilding every 3 years or so. Also, the pressures are balanced so breathing is effortless at all altitudes.

Bill Daniels