Rotatable filter assembly and method of operating same

In combination with a rotatable filter assembly intended primarily for separation of fibers from a fiber suspension and including a plurality of annular filter discs each having a plurality of filter elements, a horizontal drum adapted to be driven about an axis and on which said filter discs are mounted in substantially parallel, axially spaced relation to eah other, a container for said fiber suspension and in which said drum is rotatable, each filter element being formed by a hollow body having walls of straining cloth and also having radially inner and outer ends, each said hollow body having a filtrate outlet at its radially inner end, said drum being generally cylindrical and including a series of tubes having axial main portions forming a grating-like mantle wall of the drum, each hollow body communicating through its filtrate outlet with a corresponding said tube forming a discharge tube, and a collecting hopper extending into the drum through an open end thereof and surrounded by said filter discs, said hopper having an upwardly facing entrance opening extending along all of said filter discs, the improvement comprising means defining accumulator chambers in which said main portions of the discharge tubes terminate, said chambers communicating through said main portions with corresponding filter elements, means forming stationary filling zone where each said chamber receives filtrate from a said main portion and all of the received filtrate is retained in the chamber while the chamber is being filled, means forming a stationary discharge zone which receives said retained filtrate from each said chamber after the chamber is displaced from the filling zone as the drum rotates, said zones being adjacent the drum, and stationary wall means separating said zones from each other to allow different respective pressures to be maintained in the zones, said chamber-defining means including walls for retaining in each said chamber, as the chamber moves from the filling to the discharge zone, a static body of filtrate including filtrate first entering said chamber at the filling zone, whereby all of the filtrate received at the filling zone by each chamber is discharged thereform at the discharge zone, said discharge zone including a discharge device dimensioned to discharge the filtralte content of each filled chamber and corresponding tube main portion.