First stage filters are small but they are absolutely critical to a diver's safety. These small filters are located at the very beginning of the regulator first stage. Their job is simple, collect debris from the air we breath. Most are metal and range from 1/4" flat circle to a larger conical shape that is able to collect more out of the air. So what is the problem? Corrosion alone has been known to decrease 1st Stage gas flow by 75%.
Scuba Diving magazine reported on a fatal dive accident in their October 2002 issue. That accident was attributed to salt water coming in contact with the filter and the filter corrosion decreasing the divers airflow by 75%. As soon as the diver dropped below 33 feet, the volume of air that was required to sustain life, was unattainable through the corroded filter. The diver quickly began to out breath his regulator and the panic that followed only made it worse. The diver ultimately died of a heart attack before reaching the surface.
Regulators should be overhauled annually. During this overhaul the filters, along with all life-limited parts, are replaced. Remember, these parts are life-limited, not dive limited which means regardless of how many dives the regulator has on it, these parts may be beyond their useful life. Underwater World inspects the filters upon removal as their color may indicate other problems with your breathing air. For example; green = saltwater corrosion, brown = rust from tanks, blue = carbon monoxide in breathing gas, black = carbon dioxide in breathing gas. It is uncommon to see blue or black but very common to see green. Saltwater gets on the filter incredibly easily. A few drops is all it takes to begin the corrosion cycle.
Divers should ALWAYS protect their filters from saltwater and ALWAYS place the dust cap on prior to rinsing the regulator. Regulators that have been rinsed without the dust cap should be inspected by a service technician for internal corrosion. Most AquaLung regulators come equipped with the patented "Auto-Closure Device" or ACD. This device protects the first stage and filter by closing itself whenever it is not hooked up to a tank.
Always remember that regulators, bcds, and dive computers are truly life-support equipment. They are designed to sustain life in an environment that without them cannot be sustained. Treat your equipment right and have it overhauled and inspected by certified service technicians.