Patent ID: 7384503

Claim:
A method for determining contaminant particles in an aqueous paper-making pulp comprising a) providing a screen assembly comprising a screen supported in a housing, said housing having first and second zones separated by said screen, a first port in said housing communicating with said first zone, and a second port in said housing communicating with said second zone, b) feeding an aqueous paper-making pulp containing contaminant particles tangentially into said first zone through said first port, thereby producing a separation of heavy contaminants from lightweight contaminants in said first zone, feeding pulp fibres and lightweight contaminants along a first flow path adjacent said screen in said first zone, and feeding the pulp fibres through said screen to deliver a flow of a screened aqueous suspension of pulp fibres from said first zone to said second zone while retaining the heavy and lightweight contaminants present in said aqueous pulp, in said first zone, c) withdrawing the screened suspension through said second port from said second zone, d) discontinuing steps (b) and (c), feeding a rinse fluid into said first zone to entrain residual pulp fibres in said first zone, and flush them through said screen as a flushed fibre suspension and withdrawing the flushed fibre suspension through said second port from said second zone, while retaining said heavy and lightweight contaminants accumulated in said first zone, e) discontinuing step (d), feeding a flush fluid into said first zone to entrain contaminant particles accumulated in said first zone, and flowing said entrained particles out of said first zone through said first port, and f) recovering the contaminant particles from said flush fluid.