Method of measuring drainage rate

In a method of measuring drainage rate of a pulp furnish for making paper products to predict how said furnish will dewater on a paper machine forming wire, the method being of the type wherein a slurry sample of the furnish is placed in a holding container having a screen bottom for separating furnish solids from slurry water, the slurry then being dewatered so as to form a wet pad of furnish solids on the screen with the water draining therethrough, the improvement comprising:

• placing a finite sample of slurry in the holding container;
• dewatering the slurry sample while subjecting it to a pressure differential created by providing a reduced pressure beneath the holding container screen while the upper surface of the slurry is exposed to the atmosphere;
• recording, simultaneously with beginning dewatering the sample, the pressure differential across the sample as a function of time throughout the entire period when water is being removed, particularly recording a first point of inflection where pressure differential decreases as air first begins to be drawn through the pad on the screen, a second point of inflection marking the point at which pad compression in response to the pressure differential effectively ends, and a third point of inflection marking the point where water is no longer being removed but air continues to be drawn through the pad;
• and
• relating said recorded points of inflection to drainage characteristics of a pulp furnish on a paper machine forming wire.