Do constant pressure filtration experiment with plate-and-frame filter press, and calculate that the compressibility index of filter cake is negative when processing the experimental results? Is this

Do constant pressure filtration experiment with plate-and-frame filter press, and calculate that the compressibility index of filter cake is negative when processing the experimental results? Is this right? What does a negative value stand for? Namely l There are mainly the following points: 1, pressure, I mean the pressure filtration of feeding, and the pressure should be gradually increased at the beginning of feeding. When the pressure reaches the allowable pressure of the plate-and-frame filter press, feed at constant pressure as much as possible. 2, the material should be uniform before and after, that is, keep the density of the material consistent. 3, plastic frame (frame 2) feed hole to prevent clogging. If the feed holes in each frame are inconsistent. It is easy to cause pressure difference. Resulting in uneven upper frame of the material.