Familiarise with High Pressure Terminology

Compressor Dictionary - C

Cartridge Lifetime

Unlike the intake filter, whose lifetime is influenced solely by ambient air quality, the » TRIPLEX filter cartridge's lifetime depends on the amount of air processed, the setting of the pressure maintaining valve and the temperature of the filter housing.

Several methods can be employed to determine the degree of saturation:

• Weighing the TRIPLEX cartridge
  The molecular sieve has a fairly low filter capacity; it absorbs merely 20% of its own weight in water. The weight of the cartridge is indicative of the residual capacity. The weight of a fully saturated cartridge is printed on the cartridge housing.
  
  
• Compressor logbook
  Filter cartridges are supplied with a logbook, which is used to record the number of fillings, filling pressure differential (final pressure minus residual pressure) and cylinder sizes. The number of fillings depends heavily on ambient temperatures. Hot climate drastically reduces filter lifetime.
  
  
• Operating hour counter
  Experienced compressor users get a fair indication about residual filter lifetime from the unit's operating hour counter. However, filter capacity depends heavily on ambient conditions; adjustments must be made for air temperature and humidity.
  
  
• Chemical indicators
  Drying agents may contain chemical indicators that change colour. Silica gel, for example, is initially blue and turns pink when saturated.
  
  
• Electronic surveillance
  Electronic devices normally monitor larger units. Once the cartridge approaches its point of saturation, a humidity sensor, which is installed close to the cartridge's air outlet, gives advance warning. If the filter is not changed, the unit switches off automatically thereafter.
  
  
• Pressure swing adsorbers or regeneration dryers
  Large units may be equipped with a special filter assembly containing two drying cartridges. While one cartridge dries the stream of humid, high pressure air, the second cartridge is regenerated by counter-flow of desiccated, low pressure air. To ensure continuous operation, the airflow is reversed after a while. The compressor's free air delivery is reduced slightly, because approx. 5% of the compressed air is depressurised, dried and used to regenerate the second cartridge. The airflow has to be reversed frequently because the drying cartridges are not regenerated entirely and, therefore, have limited absorption capacity. The regeneration dryer does not purify air; an activated carbon filter must be connected in series to achieve optimum breathing air quality.

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