That is an oil bath type. disassemble over a catch pan as the lower pan has or should have engine oil in it to trap dirt.
It is assembled with ring clamps, loosen the screws in bottom one and take the lower pan off, and replace the oil and dirt with fresh clean oil. That is about all of the maintainance required. The center section has a wire mesh in side, and oil bubbles up in that gaining surface area to catch dirt. They actually work quite well, but are messy to service.
Regards, Kirk