2200900943 is an inlet valve rebuild kit that contains all parts needed to rebuild the inlet valve. It is recommended to use this kit every 8,000 hours or 2 years. If your compressor is slow to build air or it leaks from the inlet valve, this kit may solve the issue. Often times this is refered to as an Unloader Repair Kit using part number 2200-9009-43 or 2200 9009 43. Your parts manual may state a description for this part as KIT SPARES UNLOADER.