a fluid actuated , valveless sanding tool is disclosed which comprises a housing containing a cylinder , a double - ended piston mounted for reciprocal movement within the cylinder , a mounting plate to which an abrasive tool can be attached , and a double rack and pinion connecting means reciprocally driving the mounting plate . a fluid supply system delivers pressurized fluid to a central portion of the bore and a vent system permits venting of the ends of the cylinder . the piston has two end seals and three internal , main seals which maintain a fluid tight relationship with the inner cylinder wall . two internal passages in the piston are in communication with the annular areas between the three main seals and the respective ends of the piston . the end seals alternately cover the corresponding vents for the cylinder ends thereby permitting the piston to be reciprocally driven by the pressurized fluid which has been alternately delivered from the fluid supply system at the central portion of the cylinder to the other respective end portions of the cylinder through the internal passages in the piston itself . hence the reciprocating piston serves as its own pressurized fluid directing valve .