The theoretical background of the mechanism of concentration in the sluice is analyzed in detail by broadly categorizing the involved mechanisms into two separate, different actions; vertical stratification in the inhomogeneous flowing suspension and the same in the moving dilated bed, beneath the former.The significance of the many design and operational variables and their interrelationships are then examined together with the modelling of the cone variables. The cone's application is also discussed.The design aspects of certain forms of sluices are analyzed to show how theoretical and operational considerations should be knitted to achieve an improved performance. Failure to obey such considerations is certain to make any sluice unpopular as is the case of Lamflo sluice.