A canister for maintaining entrained particles in a gas stream passing there through. The canister has an outer annular member and an inner porous annular member. The inner porous annular member has rings with at least one expansion zone in each ring. An annular interior volume is between the outer annular member and the inner porous annular member. A gas source is in flow communication with the annular interior volume for providing gas at a pressure sufficient to pass through the inner porous annular member to dislodge particles adhering thereto.