Explain the purpose of a coalescer in a compressed air system.

The purpose of a coalescer in a compressed air system is to remove liquid aerosols, primarily oil and water, from the compressed air. Compressed air often contains contaminants such as oil from the compressor lubricant, water vapor that condenses as the air cools, and solid particles. While filters can remove solid particles, they are not as effective at removing fine liquid aerosols, which are tiny droplets suspended in the air stream. A coalescer works by forcing the compressed air to flow through a specialized filter medium. This medium is designed to cause the small liquid droplets to combine or "coalesce" into larger droplets. As the air passes through the coalescer element, the small liquid droplets impinge on the filter fibers and merge together. These larger droplets then flow down the filter element due to gravity and are collected in a sump at the bottom of the coalescer. The collected liquid is then typically drained away automatically. By removing liquid aerosols, a coalescer prevents damage to pneumatic tools and equipment, reduces corrosion in the air distribution system, and improves the quality of the compressed air for applications where clean, dry air is essential.