With regard to the Motor Player Corp. turbine pump : I have
restored one of these units which did have sawdust as insulation.
Perhaps different materials were experimented with.

I wasn't overly impressed with the engineering but it worked very
well and was reasonably quiet.  The power was supplied through
a large resistor housed in a perforated metal box (Australia uses
240 volts 50 Hz power).

Best wishes,
Brian Butler
Swan Hill, Australia