The 2" Guinevere Inflatable Sander are pumped up through an air inlet in the drive shaft located in the bottom of each sander. The molded rubber bulb constantly flexes and changes shape conforming to the shape it is pressed against. It should be inflated with the minimum amount needed to hold the rubber bulb on the mandrel. To inflate use the optional Guinevere Pump. Do not use compressed air as it can damage the unit.