bleed hole and are conducted directly into the internal passage 45 with a minimum of impaction upon the outer working surfaces of the seal the integrity of the seal teeth are thus preserved and the operating life of the seal is considerably extended when compared to other seals operating under similar conditions the internal passage 45 contained in the seal body beneath the labyrinth cavities is vented to an area of lower pressure exposing the passage to a source of lower pressure has a twofold effect in that it places a suction pressure on the bleed holes thus helping to draw contaminants out of the cavities and also serves to remove the contaminants collected in the passage out of the seal area venting is achieved in the present embodiment of the invention by placing the passage in fluid flow communication with the diffuser at the exit region of the turbine wheel which is at a much lower pressure as illustrated in fig1 an enclosed flow channel referenced 55 extends from the side wall entrance to the passage 45 to the diffuser region 26 the flow channel is arranged to pass around or through the machine casing 19 span across or through the nozzle ring 22 and the shroud 25 and opens into the diffuser at some point downstream from the turbine wheel 11 whereby particulate material drawn from the seal region is carried out of the machine with the discharge flow it should be clear to one skilled in the art that the flow channel used to vent the passage 45 may be coupled to an external suction pump that is arranged to.