Ok BOB a bit about vacuums, he did say small and I use this one continually as a small ,handy one for drywall and sawdust.
So after 29 years rebuilding vac motors, selling vacuums and cutting drywall for central vac retro fits......IMHO if you want heavy duty and quality I don`t know industrial by current brands in your area but I can tell you about filtration and fine dust.
Nestor hit the nail on the head. We used to test them with 5 lb bags of flour
. A standard paper filter will clog fast since the filter is limited to it`s surface area and paper just clings. A hanging auxilary filter had at least 4 times the surface area to begin with, hence prolonged suction. The same principle of surface area is found in todays extra thick furnace filters and a Toyota oil filter... more surface area provides more filtering ability. Just cut one of these open and lay all the filter media flat versus a standard one and you`ll see what makes them work
We used to take an industrial and equip it with a dacron filter, reusable and washable which would hang down inside the tank. Being a slippery surface it would shed the dust and continue to suck more than 4 times the capacity of a standard paper filter unit and maintain enough air flow to still pick up 4 x 1 inch steel balls bearings. When your paper filter clogs you loose air flow.
Today we are seeing more synthetics in filtarion so look for something that can be equipped with a secondary elastisized filter or has a slippery internal filter and you`ll get longer motor life and better continual air flow which most people call ``suction``. Look at the hose for flex and the tools for lock on grip and universal fit where possible...And find a solid tank lock device and good wheels