The breathing performance of regulators is a measure of the ability of a breathing gas regulator to meet the demands placed on it at varying ambient pressures and temperatures, and under varying breathing loads, for the range of breathing gases it may be expected to deliver. Performance is an important factor in design and selection of breathing regulators for any application, but particularly for underwater diving, as the range of ambient operating pressures and temperatures, and variety of breathing gases is broader in this application. A diving regulator is a device that reduces the high pressure in a diving cylinder or surface supply hose to the same pressure as the diver's surroundings. It is desirable that breathing from a regulator requires low effort even when supplying large amounts of breathing gas as this is commonly the limiting factor for underwater exertion, and can be critical during diving emergencies. It is also preferable that the gas is delivered smoothly without any sudden changes in resistance while inhaling or exhaling, and that the regulator does not lock up and either fail to supply gas or free-flow. Although these factors may be judged subjectively, it is convenient to have standards by which the many different types and manufactures of regulators may be objectively compared.
Various breathing machines have been developed and used for assessment of breathing apparatus performance. Ansti Test Systems developed a turnkey system that measures the inhalation and exhalation effort in using a regulator, and produces graphs indicating the work of breathing at the set depth pressure and respiratory minute volume for the gas mixture used. Publishing results of the performance of regulators in the ANSTI test machine has resulted in performance improvements.
Applications
Breathing performance of the regulator is relevant in all circumstances where a demand regulator is used to provide breathing gas. In some of these applications, a very basic regulator will perform adequately. In other applications, the performance of the regulator may limit the performance of the user. A high-performance regulator for a given combination of gas mixture and ambient pressure will provide a low work of breathing at high RMV.
Another aspect of breathing performance is demand regulator performance in cold water, where a high flow rate may cause chilling sufficient to lock up the mechanism with ice, which usually causes a severe free-flow with consequent loss of breathing gas, which can only be stopped by shutting off the cylinder valve.
Scuba diving – All breathing gas is carried in high-pressure cylinders by the diver Recreational scuba diving – Air and nitrox at ambient pressures up to about 30 msw Technical diving – Ambient pressures may significantly exceed 30 msw Mixed gas – Breathing gases containing helium to limit narcosis and work of breathing Decompression gas – Breathing gases with high oxygen partial pressures, generally not very high ambient pressure Surface-supplied diving – Breathing gas supplied from the surface at a wide range of depths Open circuit – Gas is released into the environment and lost on exhalation Breathing gas reclaim systems – Helium based breathing gas is returned to the surface for recycling via an exhaust regulator to save expensive gas Built-in breathing systems in hyperbaric environments – High oxygen content gas is vented to the exterior via an exhaust regulator to avoid high fire risk. High performance not generally needed, as the user is normally resting. Oxygen administration for first aid in diving accidents – High oxygen fraction at surface pressure, fairly low flow rate, but user may be injured and have difficulty breathing. Breathing apparatus for work in unbreathable atmospheres – Usually at ambient pressures close to normal atmospheric pressure, breathing air. Work rate can be high but should not be extreme. Positive pressure breathing may be used in toxic atmospheres to reduce risk of contamination due to leaks. Self-contained breathing apparatus (SCBA) for rescue and firefighting – Users may have to work hard in difficult conditions, but pressure range is generally close to normal atmospheric pressure. Work rate may be extreme in emergencies. Positive pressure masks may be used, which will offset the pressure graph, but not necessarily increase the net work of breathing. Emergency breathing gas supply in submarines (BIBS) – Survival conditions, at unpredictable pressures. Oxygen supply for unpressurized aircraft – Low ambient pressure due to high altitude. Air supply enriched by additional oxygen. Flow rate not expected to be very high