Abstract: A the operation of pulp screening apparatus may be improved by employing a multi element foil having a leading foil section and a trailing foil section spaced from and trailing leading section so that adjacent surfaces of the sections one formed by a portion of a pressure side of the leading section and the other by the leading end of the trailing foil section define opposed walls of a passage for fluid directing fluid flow from the pressure side of the leading foil section to a cambered low pressure side of the trailing section. The angle of attack (?) of the complete multi element foil is set to be significantly less than the angle of attack (?) of the trailing foil section to increase the negative pressure pulse generated by the trailing section and thereby improve operation of the screening device.

Abstract: A the operation of pulp screening apparatus may be improved by employing a multi element foil having a leading foil section and a trailing foil section spaced from and trailing leading section so that adjacent surfaces of the sections one formed by a portion of a pressure side of the leading section and the other by the leading end of the trailing foil section define opposed walls of a passage for fluid directing fluid flow from the pressure side of the leading foil section to a cambered low pressure side of the trailing section. The angle of attack (&agr;) of the complete multi element foil is set to be significantly less than the angle of attack (&thgr;) of the trailing foil section to increase the negative pressure pulse generated by the trailing section and thereby improve operation of the screening device.