Copyright Goodheart-Willcox Co., Inc. 408 Fluid Power reach a predetermined level. The valve resets after sys- tem air pressure forces the accumulated liquid and dirt out of the bowl. Factors that must be considered when selecting a fi lter unit for a workstation include: • Conductor size on the fi lter body. • Pressure rating of the fi lter body. • Particle size (in microns) of the contaminants the fi lter will remove. • Airfl ow rating of the fi lter. • Pressure drop across the unit at the airfl ow rate required by the system. • Need for special features such as pressure gauges and automatic drains. fi ltering unit is swirled. This causes any water, oil drop- lets, or solid particles to be thrown against the walls of the fi lter case. These materials then settle by gravity to the bottom of the fi lter bowl where they can be physi- cally removed during system service. The air then passes through a series of small holes in the porous material. The porous material traps particles, which are removed during fi lter replacement or cleaning. Figure 16-16 shows the internal structure of a typical fi lter. The water, oil, and dirt that accumulate at the bot- tom of the fi lter bowl need to be periodically removed. The fi lter bowl is often equipped with a draincock to facilitate this service, Figure 16-17. Opening the valve allows system pressure to force the liquid and dirt out of the bowl. Automatic draincocks are available. These valves automatically open when the liquid and dirt Air- distribution line Filter Regulator Lubricator Used with permission of CNH America LLC Figure 16-15. Final air preparation at the workstation is provided by a unit that consists of an air filter, pressure regulator, and air lubricator. This unit is known as an FRL unit. Airflow Make connections on top of horizontal lines Airflow Slope Slope DeVilbiss Air Power Company Figure 16-14. Workstation drop lines should be attached to the top side of distribution lines to prevent liquid water from draining into the workstation. This arrangement also reduces the entrance of rust and scale that has formed in the main distribution lines.