1. IN A CONCENTRATING PROCESS IN WHICH A PULP OF WATER AND FINELY DIVIDED SOLIDS FEEDS INTO A PUMP BOX, ADDITIONAL WATER IS INTRODUCED TO THE PUMP BOX TO DILUTE THE PULP AND THEREBY DECREASE ITS DENSITY, THE VOLUME OF THE ADDITIONAL WATER IS REGULATED TO MAINTAIN A SUBSTANTIALLY CONSTANT LEVEL OF DILUTED PULP IN THE PUMP BOX, A PUMP TRANSFERS A CONSTANT VOLUME OF THE DILUTED PULP IN SHARES TO A BANK OF PARALLEL SPIRAL CONCENTRATORS, AND THE CONCENTRATORS SEPARATE SOLIDS IN THE PULP INTO CONCENTRATE AND TAILINGS PRODUCTS, THE COMBINATION THEREWITH OF A CONTROL METHOD COMPRISING GENERATING A SIGNAL REPRESENTATIVE OF THE DENSITY OF THE DILUTED PULP BEFORE IT REACHES THE CONCENTRATORS, CUTTING INDIVIDUAL CONCENTRATORS IN THE BANK INTO AND OUT OF OPERATION IN RESPONSE TO CHANGES IN SAID SIGNAL, AND RETURNING TO SAID PUMP BOX THE SHARES OF PULP FOR CONCENTRATORS CUT OUT OF OPERATION TO COUNTER THE DECREASE IN DENSITY BROUGHT ABOUT BY THE ADDITIONAL WATER, THEREBY MAINTAINING THE PULP IN THE CONCENTRATORS AT A RELATIVELY CONSTANT DENSITY AND MAINTAINING A RELATIVELY CONSTANT WEIGHT OF SOLIDS IN EACH CONCENTRATOR IN OPERATION.