Familiarise with High Pressure Terminology
Compressor Dictionary – C
Checking Breathing Air
Minimum standards for the purity of breathing air are defined by the DIN EN 12021 (former DIN 3188) norm. These guidelines are valid up to a depth of 50 metres and a dive time of up to 2 hours. Air has to be tasteless and odourless, the level of carbon monoxide may not exceed 30 ml/m³, the level of carbon dioxide is restricted to 800 ml/m³.
The restriction of the water content is also of importance because it prevents corrosion inside the breathing air cylinders and stops regulators from free flowing in cold waters.
Unlike other national standards, which have no stipulated restriction on water vapour, the DIN EN 12021 (former DIN 3188) norm lays down a maximum level of 25 mg/m³ (of 35 mg/m³ for final cylinder pressures of 200 bar to 300 bar). These values refer to the quality of air delivered by the compressor. These restrictions are less severe for air quality measurements performed directly on breathing air cylinders, where the limit is set at 50 mg/m³ (at 35 mg/m³ for final pressures over 300 bar).
Air quality is checked using special test sets. A precise quantity of air is slowly passed through the set. By changing colour, indicators inside the apperatus help determine the level of contamination with respect to specific substances (carbon monoxide, carbon dioxide, water or hydrocarbons, for example). The tests ought not be performed right after the compressor is started, since this will produce inaccurate results.
The level of carbon dioxide in the atmosphere is around 350 to 400 ppm. After heavy-duty use of the compressor, the molecular sieve, which traps some of the carbon dioxide under pressure, may contain substantial levels of this gas. The absorbed carbon dioxide is emitted once the pressure drops. If the compressor is restarted, high levels of carbon dioxide may enter the first cylinders.
To avoid this, we recommend that the compressor be vented for 1 – 2 minutes before connecting cylinders and performing air quality tests. Before opening the outlet valve, please secure the filling hose. This will prevent potential injury from a filling hose lashing about uncontrollably.
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