A pressurized fluid flow system for a reverse circulation down-the-hole hammer having a cylinder coaxially disposed in between an outer casing and the piston. This piston reciprocates due to changes in pressure of the pressurized fluid contained inside of a front chamber and a rear chamber at opposite sides of the piston, where the flow into and out of these chambers is controlled solely by the overlap or relative position of the piston and the cylinder as a supply chamber and a discharge chamber, which are defined by recesses on the inner surface of the outer casing and separated by a dividing wall, respectively, supply to and discharge from the front and rear chambers, the pressurized fluid. An internal chamber may also be provided in between the piston and a sampling tube coaxial with the outer casing for a more efficient filling of the chambers.