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US Navy Test for Scuba

The US Navy test has similar criteria to EN250 except the temperature is more extreme. The US Navy requires regulators to operate at sub zero. EN250 will test down to 2-4 celsius whereas the US Navy test goes down to minus 2 celsius. Cold water scuba equipment has to have extra function and utility as opposed to standard equipment.

Here the the diver has two regulators because of the significant risk of free flowing regulators. When air flows rapidly through a small aperture the surrounding material cools down rapidly, so ice forms on both first and second stages in very cold water. To combat this problem manufacturers use design to warm the breathing apparatus and also prevent water entering it. Also it is important to have a redundant regulator in case the primary regulator get frozen causing a free flow. These are using mounted on H or Y valve on high capacity cylinders or alternatively twinsets are used.

Frozen First Stage

Cold Water Regulator Design

The regulator’s first stages are environmentally sealed and filled with material such as crystal lube or silicone oil. This prevents water entering the first stage that would otherwise freeze and the lubricants replace air inside the regulator’s space usually around the biasing spring where ambient water would normally flow into. If air remains in this space the moisture in this air would easily freeze so it is replaced. The main important design feature is to have the regulator constructed with a material that has a high thermal conductivity. In relative terms the ambient water is much warmer than material which the compressed air flows through, so this ambient warmer water will warm up the material if there is good thermal conductivity. Materials that have good thermal conductivity such as Aluminium Alloys, Stainless Steel, Brass, Carbon Fibre rather than Titanium and Plastic. More advance designs used different air flows and have coatings with prohibit Ice formation. All manufacturers have to pass the EN250 test in Europe but not many manufacturers product regulators that pass the US Navy Test. Those that do often have US Navy or USN in their designation.