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The "double hose" regulator Demone Mark II was produced from 1962 to 1965 by the Demone Manufacturing Company, Oak Lawn, Illinois. The company was founded by Al O'Neill and Robert (Bob) J. Dempster. The Demone was designed by him.

Basically, the Demone Mark II is a double Mark I single hose. It also features a stiffer hose system than other double hose regulators. Despite the extra protection offered by corrugated hoses, the buildup of sand and salt is unavoidable, which can lead to even greater effort by the diver to exhale air through the exhaust hose. 



The regulator's sales marketing asserted that the Demone was the first hydrodynamically designed regulator. He had two second stages. One would backup if the other failed. Two thin hoses of the same hose configuration used for company's single hose MARK I regulator were inserted in the corrugated hoses. The exhaled bubbles were carried to the back of the diver's head.



This was one of the downsides of this regulator model: The exhalation was hampered as the diver made a great effort to carry the exhaled air through the dead space of the corrugated exhalation hose. 

The regulator tried to bring the advantages of a single hose regulator to lovers of the double hose regulators used by Mike Nelson. Despite its elegant design, it did not last long in the market.




Both, a ‘single’ and ‘two stage’ configuration, were assembled as one unit and commonly mounted on the cylinder set behind the diver’s shoulders. A pair of large diameter corrugated rubber hoses run from this unit, one over each shoulder, to the mouthpiece. One hose carried the inhalation air to the diver and the other the exhaled air back to the exhaust valve mounted within the regulator unit.

The hoses were not pressurised and transported air at ambient pressure (water pressure at depth). The first stage reducing valve, which is attached directly to the cylinder, delivers air at a pressure of around 10 bar into a small diameter hose which is attached to the mouthpiece assembly. This assembly contains the second stage which deliver air on the diver’s ‘demand’ and has an integrated exhaust valve which discharge exhaled air adjacent to the diver’s face.

The Demone Mk I was a single hose regulator with the first stage mounted on the cylinder. A single hose, at intermediary pressure, delivered air to a mouthpiece second stage. It is with the exhaust valve that the unique design of the Demone manifests itself.



A single large corrugated rubber hose, very similar to that used on double hose regulators, was laid back over the delivery hose to carry the exhaled air over the diver’s shoulder to discharge the exhaust behind him.





The Demone"s MkII design has introduced a duplexal system. There is still a single 1st stage valve on the cylinder and a pair of hoses, one over each shoulder, led to the mouthpiece demand valve. The transverse mouthpiece has a single diaphragm, but two second stage valves, one on either side. The concept being that should one valve fail then the other would continue working. 



A pair of exhaust valves in the mouthpiece demand valve then directs exhaled air into two exhaust hoses enveloping the hoses to send off the exhalation air behind the diver’s head.

The "double Hose" Demone II is, surely, a "quadruple" hose regulator with two delivery hoses, at intermediary pressure, and two exhaust hoses, working at ambient pressure.



To prevent the air filled hose from inducing a free-flow condition in the second stage four small flap valves were introduced at the mouthpiece end of the hose. 

The Demone's MK II design was not enough to ensure its survival on the market. Unfortunately, the regulator did not command a large market and faded away although his company continued to manufacture other sport diving equipment as Demco Products. After only a few years the Demone production ceased.

Robert J Dempster died in April 2006.




1. http://www.sandiegodiving.com/education/items/13.html

2. Basic Scuba by Fred M. Roberts (1963)

3. The Demone Regulators - Historical Diving Times - No 42 Summer 2007

4. Drawings - Bob Campbell - "Copyright Historical Diving Society"

5. Basic Scuba, Fred M Roberts, D Van Nostrand Co Inc - 1962.


Mark I #J433

Mark II #D260

 Mark II #J382

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