Self cleaning centrifuge drum with stepwise variable closing pressure

Claim 1

In a centrifugal separator constructed for intermittent discharge of sludge, comprising: a. a rotatably mounted separator drum having an upper end member and a lower end member defining a separating and sludge chamber, at least one sludge discharge passageway disposed at the radially outward periphery of the drum, b. one of said end members including a piston valve movable axially within said chamber to open and close the sludge discharge passageway for desludging, d. a fluid operated piston valve control means for alternatively forcing the piston valve to the closed position by the pressure of a control fluid and permitting the piston valve to move to an open position by relieving the pressure of the control fluid, d. control fluid routing means for pressurizing and depressurizing of control fluid for controlling the position of the piston valve, the improvement which comprises: e. said piston valve having an axially outwardly disposed surface, and said drum having a surface confronting said surface of the piston valve, said piston valve control means comprising a plurality of closing chambers disposed in radial succession from the axis, concentric slide seals between the axially outwardly disposed surface of the piston valve and said confronting drum surface, providing said plurality of closing chambers, f. said control fluid routing means comprising means for selectively pressuring and depressurizing of the closing chambers permitting selection of the force imposed on the piston valve.