Suction Valve Head Unloaders For continuous running air compressors, unloader lets unit idle load-free until air supply drops to cut-in pressure; automatically lets unit idle again after high pressure limit is reached. Heavy-Duty Stainless Steel Valves Lapped to optimal flatness for high efficiency and extended wear. Large Intake Filter Silencers For quiet operation and provides maximum particulate protection. Deep Finned Cylinders and Heads Ensures cool, vibration free operation and long life. Cast Iron Cylinders Precision bored for high performance and low oil carry-over. Rings Long-life industrial design compression and oil rings for maximum performance. Cast Iron High Tensile Strength Rods With replaceable rod bearings and pin bushings. Machined to close tolerances for many years of service. Ductile Iron Crankshaft Dynamically balanced, precision-machined, and ground. Assures extended running life for all internal bearings and wearing surfaces. Balanced Flywheel For strength and durability. Large Main Roller Bearings Precision fit to hold alignment of all rotating parts. Oil Sightglass Conveniently located for reading oil level in crankcase.