Greetings,  The only insulation in a Motor Player turbine pump box
should be heavy felt used for sound isolation.  If there is particulate
junk inside, it was something that was sucked in from the outside.

I am not aware of any filters used in these pumps but there could be
variations that I have not seen.  It is important that there not be
any garbage lodged in the turbine fans as this will cause unbalance,
vibration and premature failure.

These are very well made pumps and will work well if the bearings are
serviced and the fans are cleaned.  The fans need to be tight on the
shaft and care must be taken in disassembly to be sure that their order
is not changed as they are closely fitted in addition to having three
different types of fan wheels in the stack.

The fans are made of an alloy with aluminum cover plates and can
develop cracks.  It is advisable to clean them with solvent to remove
contaminants that might cause further deterioration.  If the original
bearings are good they can be cleaned and repacked with a high
temperature grease, otherwise the bearing can be replaced with modern
sealed bearings with a little machining of the motor housing and
careful shimming.

I recently overhauled one of these and had it rewound with class F
insulation.  It can now be run without worrying about the original
cotton covered wiring overheating.  I had it dynamically balanced after
it was rewound.  Before doing this, I carefully removed a lot of rough
metal from the fans and it is very quiet now and develops more vacuum.

Best regards,
Spencer Chase
Laytonville, Calif.
http://www.spencerserolls.com/