The California Air Tools 20040DCAD Ultra Quiet and Oil-Free Air Compressor is designed to be one of the quietest 4.0 HP air compressors in the industry having only 75 dBs of sound. The powerful two 2.0 HP motors operates at only 1680 RPM creating less noise, vibration and creating less wear. The Oil-Free Dual Piston Pump System is engineered for longevity, high performance and durability. The SP-90407 Motor/Pumps are tested for a minimum pump life of 3000 hours before service. 30% more life before repair. The large 20.0 Gal. steel air tank is the right size for most all locations. The Air Dryers are specially designed to remove the water vapor from the air to protect sensitive tools and machinery. To dry the air from the air compressor an after cooler and dryer are utilized. The after cooler is a heat exchanger for cooling the discharge air from the air compressor. The water vapor from the compressed air is condensed into liquid form and pushed into the Air Dryer. The California Air Tools EZ-1 Automatic Drain Valve has been designed to eliminate manually draining your air compressor air tank. The manually set timer allows you to set the time for both the frequency and duration of the draining process. This air compressor is ideal for anyone working inside.