INTERNALLY FED SCREENS

Pros
►Ideally suited for removal of fibrous solids.
►Ideally suited for removal of solids that have shear resistant properties.
► Ideally suited for removal of solids that are not amorphous or do not smear under some pressure.
► These screens provide more retention time on the screen surface and thus you typically have a drier mass of solids being discharged from the screen.
► In many applications, you can alter the influent distribution piping to enhance transition of liquids/solids to the screen surface.
► The design permits the changing of the elevation of the solids discharge area, providing a drier mass of solids being discharged from the screen.
► The design permits liquid/solids separation in applications where there are very high flows.
► Reduced maintenance time & cost.

Cons
► Typically, require sophisticated cleaning systems to keep the screen clean.
► Typically, screen cleaning requires large amounts of water and high pressure.
► Liquid/solids separation very difficult when solids are amorphous and or have lower shear tolerance.
► Typically, not well suited for liquid/solids separation applications where oils and grease levels are of concern.

EXTERNALLY FED SCREENS

Pros
► Typically, well suited for liquid/solids separation applications when a wide range of solids are present.
► Better control of influent conditions.
► Better control of liquid/solids interface with screening surface.
► Better control of liquid levels in the influent chamber/ velocity & depth.
► Better cleaning of screen surfaces, due to the internal back washing activity provided by the filtrate. Typically, this is referred to as the self cleaning phenomenon, caused by the constant back washing.
► Designs provide other cleaning approaches, all of which require less water and pressure.
► Designs provide for a wide variety of influent piping scenarios.
► Designs provide better control of screen rotation to enhance liquid/solid separation.
► Well suited for applications where oils and grease are present.
► Designs provide simple overflow bypass configurations, when upset conditions are experienced.

Cons
► Not well suited for very high flows, when fine screening is required.
► Solids discharged from the doctor blade have the potential of being wet.
► Potential exists for free water/oils to be discharged with the solids.

Dontech Industries Inc.
76 Center Drive, Gilberts, IL 60136
Telephone: 847-428-8222 / FAX: 847-428-6855