Pressurized fluid flow system for a reverse circulation hammer

A pressurized fluid flow system for a reverse circulation down-the-hole hammer, the hammer comprising:

• a cylindrical outer casing (1);
• a rear sub (20) affixed to the rear end of said outer casing (1) for connecting the hammer to the source of pressurized fluid;
• a centrally-bored piston (60) slidably and coaxially disposed inside said outer casing (1) and capable of reciprocating due to the change in pressure of the pressurized fluid contained inside of a front chamber (240) and a rear chamber (230) located at opposites sides of the piston (60), the piston (60) having multiple inner sliding surfaces (69) and outer sliding surfaces (64);
• a drill bit (90) slidably mounted in the front end of the hammer on a driver sub (110), the driver sub (110) being mounted in the front end of the outer casing (1);
• and
• a sampling tube (130) coaxially disposed within the outer casing (1) and extending from the drill bit (90) to the rear sub (20);
• the sampling tube having an outer sliding surface (132);
• wherein the pressurized fluid flow system comprises:
• a cylinder (40) disposed coaxially in between the outer casing (1) and the piston (60);
• a supply chamber (2) for supplying pressurized fluid to the front chamber (240) and to the rear chamber (230), and a discharge chamber (3) for discharging pressurized fluid from the front chamber (240) and from the rear chamber (230), the supply and discharge chambers (2, 3) defined by respective recesses on the inner surface of the outer casing (1);
• the supply and discharge chambers (2, 3) being internally delimited by the cylinder (40) and separated by a dividing wall (5);
• the supply chamber (2) being in permanent fluid communication with the source of pressurized fluid;
• the discharge chamber (3) being in permanent fluid communication with the bottom of the hole being drilled by the hammer;
• multiple supply and discharge through-ports (42, 43) provided in said cylinder (40) respectively facing the supply and discharge chambers (2, 3);
• the piston (60) having:
• an internal chamber (74) defined by a recess on the inner sliding surfaces (69) of the piston (60) and delimited by the sampling tube (130), the internal chamber (74) being in permanent fluid communication with the supply chamber (2);
• a first set of fluid-conducting means (67) for allowing said permanent fluid communication between the internal chamber (74) and the supply chamber (2);
• a second set of fluid-conducting means (66) for connecting the outer sliding surfaces (64) of the piston (60) with the rear chamber (230) and channeling the flow of pressurized fluid from the rear chamber (230), through multiple discharge through-ports (43) of the cylinder (40), into the discharge chamber (3);
• and
• a third set of fluid-conducting means (81) for connecting the outer sliding surfaces (64) of the piston (60) with the front chamber (240) and channeling the flow of pressurized fluid from the front chamber (240), through multiple discharge through-ports (43) of the cylinder (40), into the discharge chamber (3);
• and
• passages (73, 77) formed in between the piston (60) and the sampling tube (130) for channeling the flow of pressurized fluid from the internal chamber (74) into the front and rear chambers (240, 230);
• whereby the flow of pressurized fluid into the front and rear chambers (240, 230) is controlled by the overlap or relative position of said multiple inner sliding surfaces (69) of the piston (60) and said outer sliding surface (132) of the sampling tube (130) during the alternating movement of the piston (60);
• and
• whereby the flow of pressurized fluid out of the front and rear chambers (240, 230) is controlled by the overlap or relative position of said multiple outer sliding surfaces (64) of the piston (60) and the inner surface of the cylinder (40) during the alternating movement of the piston (60).