Abstract: Sintered glass pellets which generally decrease in particle size as they increase in specific gravity provide a unique filter medium which varies from larger pellets at its inlet (upstream) upper portion to smaller pellets at its outlet (downstream) lower portion. In view of the variation in specific gravity, particles forming the filter medium generally resume substantially their initial respective positions after the medium is back-flushed for cleaning. Although pellets throughout the medium differ in specific gravity, they are made of the same ingredients. The individual pellets are formed by granulating finely-ground glass with a suitable binder and sintering the resulting granules.

Abstract: A method and apparatus for controlling the operation of gravity or pressure filters in a filtration system. A bank of filter beds are provided for removing suspended solids from the fluid medium which are fed to the filters via a common inlet conduit. Each of the filters has an associated effluent conduit which, in turn, has a throttling device positioned therein controlling the rate of flow of the fluid medium through the respective filter. A differential pressure transmitter is provided for each filter bed to measure the differential fluid pressure thereacross and to provide an output analog signal proportional thereto. A control device generates a control signal in response to the output from the differential pressure transmitter and a set point signal representing the desired differential pressure.