A technique facilitates tool operation with mobile pistons submitted to differential pressure. The technique utilizes a mobile piston slidably mounted in a corresponding piston passage. The piston passage is defined by a passage wall surface, and the piston may be moved linearly along the piston passage under the influence of an actuating fluid or to pump a fluid. The exterior surface of the piston and/or the passage wall surface have a groove or a plurality of grooves located and arranged to collect particulates from the fluid. Removal of the particulates facilitates actuator piston function by reducing, for example, third body abrasion and jamming of the piston.