As you descend within the water, the ambient pressure increases at a rate of about 1 kg/cm2 for every 10 meters. deep. The musculature of the rib cage is capable of pumping air into our lungs winning only a slight difference in pressure between our mouths and carried out by means of our lungs. So when we dive into the water we need some device or talent that you provide air (or breathing gas), exactly the same pressure that is our environment (pressure will vary with changes in elevation).
On the other hand, this air must be supplied in the amount (caudal) necessary in every situation of demand (variable respiratory rate and volume ventilated by the lungs in each respiratory cycle) depending on the physiological characteristics of individual and the situation where you are (fatigue, stress, temperature, etc.).. This flow must be provided, of course, with minimal effort. Our air reservoir (bottle) is changing its pressure as we consume its contents. The respirator should not acknowledge this change and maintain their performance throughout the dive.
The device in question is called a demand regulator, as the air supply is not continuous but is produced when requested by our breath.
is important to clarify concepts such as flow and respiratory effort .
every breath a given respiratory rate, our lungs air the same volume of air, whether we are on the surface as if we are 30 meters. deep. However, in this volume of air surface is 1 atm. pressure and 30 mts. that volume of air at 4 atm. (1 atm. + 3 atm surface. Column of 30 meters. Of water). Ie we are moving the same volume but four times more dense. In our controller we are asking four times the flow. So consumption will also four times higher).
Another thing different is the effort (depression) that my lungs must exert to keep open the regulator valve and get that much air.
This effort must be as small as possible and measured in millibars (mbar ) or equivalently cm. water column (cm.c.H2O) . Will be negative during inhalation and positive during exhalation.
The air we breathe heavier as we descend. Therefore expected that the effort needed to breathe increases with depth and it is. In fact, the effort required to exhale through the regulator increases progressively with depth. However, there are engineering discoveries as the Venturi effect to make, during inhalation, the controller may put even more "soft", if well designed. Maintain controlled Venturi effect, without being over-pressure at any depth is another story. But do not run and go step by step.
For the amount of air flow or to ask a controller unit of measurement are liters / minute .
In order that a regulator has a low inhalation effort and nice behavior that controller must be submitted to a depth of 50 or 60 meters. (According to EN250 standard and U.S. Navy standards, respectively) and request a rate much higher than normal use.
Obviously for this to be objective, you must perform these tests with a breathing simulator contained in hyperbaric chambers, which reproduce the extreme operating conditions, obtaining measurements of effort and special graphics. The test conditions and interpretation of results were established first by the U.S. Navy and collected by the European Standard EN250.
Operation
regulator
used in scuba diving bottles filled to 200 atm. (In ground equipment such as fire, used bottles to 300 atm.). The regulator is going to reduce the variable pressure during immersion at ambient pressure. It would be virtually impossible to achieve a constant performance and the sensitivity required in a pressure reduction alone. Therefore, this pressure reduction is done in two stages. Even former regulators bitráquea were two stages (except for some very archaic model). In these two stages were built in the same metal body reported by a drill. In the current two-stage regulators are separated and linked by a flexible hose.
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