Air filters

AIR FILTERS

1. What are Air Filters ?

• Functions: The function of air filters is to remove all foreign matter and allow dry, clean air to flow without restriction to the regulator and then on to the lubricator.

• Filters are available in wide ranges starting from a fine mesh wire cloth (which only strains out heavier foreign particles) to elements made of synthetic materials (which are designed to remove very small particles).

• Usually in-line filter elements can remove contaminants in the 5 to 50 μm range. 

2. Factors Affecting Selection of Filters

While selecting the filters, the following factors at least should be taken into account : 

1. Size of particles to be filtered from the system.

2. Capacity of the filter.

3. Accessibility and maintenabflity.

4. Life of the Filter.

5. Ability to drain the condensate.

3. Construction

The construction and operation of a typical cartridge-type filter system is illustrated in Fig.11.8(a).

It consists of the filter cartridge, deflector, plastic bowl, baffle, water drain valve, etc.

4. Operation

The air to be filtered is allowed downward with a swirling motion that forces the moisture and the heavier particles to fall down. The deflector used in the filter mechanically separates the contaminants before they pass through the cartridge filter. The filter cartridge provide a random zig-zag passage for the air flow. This type of air flow arrests the solid particles in the cartridge passage.

The water vapour gets condensed inside the filter and is collected at the bottom of the filter bowl. Also heavier foreign particles that are separated from the air are collected at the bottom of the bowl. Then the accumulated water and other solid particles at the bottom of the filter bowl are drained off with the use of an on-off drain valve located at the bottom of the filter bowl.

5. Graphic Symbol

Fig.11.8(b) shows the graphic symbol for an air-filter.