Name the three stages of a pneumatic system's FRL unit and their purpose.

• A. Filter removes particles; Regulator maintains pressure; Lubricator introduces oil to lubricate components.
• B. Valve controls flow; Pump increases pressure; Sensor monitors pressure.
• C. Condenser cools air; Humidifier adds moisture; Filter removes particles.
• D. Filter removes particles; Regulator maintains pressure; Lubricator introduces oil to lubricate components.

Answer: (D)

In a pneumatic FRL unit, air conditioning is achieved through filtration, regulation, and lubrication. The filter removes particles and condensate to protect components and prevent damage or sticking in valves and cylinders. The regulator then reduces the high-pressure air to a steady, usable pressure for the system and tools. The lubricator adds a light oil to the air so moving parts stay lubricated, reducing wear and helping seals seal smoothly.

This arrangement is why the answer that lists filter, regulator, and lubricator with their respective purposes is best. The other options include components or roles not part of the standard FRL stages (such as pump or sensor, or cooling/humidification elements that aren’t typically in an FRL), so they don’t describe the usual three-stage conditioning sequence.