Filter press

Claim 1

A recessed-plate filter press, comprising: A. a plurality of composite filter plates, movably supported on side bars secured to front and rear frames of said filter press, eaCh comprising: 1. a core plate having projecting edges, formed along the peripheries of both front and rear faces thereof, and a recessed plane, surrounded by said projecting edges, in each of said front and rear faces, comprising: a. a tranversely extending main filtrate discharge channel in a side portion of said core plate; b. a filtrate discharge channel extending from said front face to said rear face and communicating with said main filtrate discharge channel; c. a pressing fluid supply channel connected to a pressing fluid supply duct and having an opening in each of said planes; and d. a centrally disposed prefilt inlet which extends transversely between said front and rear planes, and 2. a pair of air-tight, stretchable sheets, each sheet being fitted to said projecting edges of each of said front and rear faces in sealing engagement therewith and forming a pressing fluid chamber between each of said planes and each of said sheets, whereby pressing fluid, entering said pressing fluid chambers through said supply channels, inflates said stretchable sheets away from said front and rear planes, each stretchable sheet comprising: a. an inside facing having numerous small pyramid-like protrusions to form a filtering face having filtrate passages therebetween, when said inside face is covered with a filter fabric; b. an opening therethrough which is aligned with said filtrate discharge channel, whereby said filtrate passages communicate with said opening and with said filtrate discharge channel; and c. a centrally disposed opening which is aligned with said prefilt inlet, said pair of stretchable sheets being joined together at the edges of said opening by an annular member which is fitted within said prefilt opening in said core plate. B. a plurality of intermediate plates, movably supported on said side bars, arranged alternately with said composite plates, and having projecting edges along the peripheries thereof which mate in sealing engagement with the projecting edges of said stretchable sheet when a filter fabric is therebetween, comprising a centrally disposed prefilt inlet which is aligned with said prefilt inlets of said composite filter plates to provide an unobstructed prefilt entrance passage; and C. a pair of filter fabrics for use with each composite plate, having a centrally disposed opening with the peripheries thereof secured to and joined with the peripheries of an annular metal member which is fitted within said annular member of said stretchable sheets, and forming a filtering chamber in communication with said prefilt inlets, whereby said main filtrate discharge channels in said aligned and alternately arranged core plates and single plates provide an unobstructed filtrate discharge passage and said filtering chambers retain a plurality of filtering cakes which are squeezed between adjacent filter fabrics when said pressing fluid is charged into said pressing fluid chambers.