Desludger type disc bowl centrifuges

Claim 1

A disc bowl centrifuge comprising a bowl adapted to be rotated about a vertical axis, means for introducing material to be processed into the bowl interior, an annular piston disposed within an annular operating chamber in the lower part of said bowl, the outer periphery of said piston defining an upwardly-extending, first annular valve member, a second downwardly-extending annular valve member contained in the wall of said bowl, said first and second valve members co-operating to form a discharge valve controlling at least one discharge port provided in the wall of said bowl, and means for introducing pressure fluid into said piston chamber, said piston being arranged to be displaceable between an upper position in which said first and second valve members co-operate to close said valve to prevent discharge of material from said bowl, and a lower position in which said first and second valve members are mutually spaced to open said valve and permit discharge from said bowl under the action of centrifugal force, said means for introducing pressure fluid into said piston chamber is such as to admit it at a pressure substantially higher than atmospheric pressure, the magnitude of said pressure being such that, when said valve is in its closed position, the pressure in said chamber beneath said piston is sufficient to hold said valve closed irrespective of the magnitude of opening forces exerted on said piston resulting from pressurisation of its upper face by process material subjected to centrifugal force in said bowl.