This method of compressor cleaning involves injecting an abrasive grit into the engine at selected power settings ( Figure 21.30.)grit used may be ground walnut shell or apricot pits. The type and amount of material and the operational procedures will be described in the AMM. The main advantage of this procedure is that allows the time between cleaning to be extended because it produces a better result. However because the grit is mostly burned up in the combustion zone of the engine, it will not give an effective cleaning of the turbine blades and vanes as the fluid.