“…At other company locations where diatomite filters are installed, agitated slurry tanks and various types of slurry pumps are used for the injection of the filter aid into the system. Such pumps require considerable maintenance and, more important, are subject to stoppages which in the present abandoned when it was found to have two serious deficiencies: [1] it caused different grades of filter aids to be fed at widely different rates varying by as much as 10: 1, and [2] it seriously damaged the structure of some filter aids, particularly the more permeable ones (which are also the more expensive grades). The next dry feeder tried was of the vibratory type, but it too provided widely variable feed rates for different grades of material and sometimes wide variations within a single grade of material.…”