I have two used central vac systems that I got for free. Next door neighbor had it in the alley waiting for the trash man. Cord was cut off, put a new one on, nothing wrong with it, works really good. I mounted it inside the garage on the wall, use it for everything.
The next spring, the neighbor two doors down, same thing. I took the central vac home, took the canvas bag filter out of the inside, which was plugged solid, put it in the wife's washing machine ( please don't rat me out on that one). Dried it out, and the vac works fine.
I had purchased a see through cyclone previously, and took both central vacs, hooked them up in series. There is a thread on the Home Shop Machinist site with the tests they did to prove that two vacs mounted in series works better than one. Placed the cyclone on top of the first one, so most of the trash goes into the canister below. Excellent suction with the two of them in series, and all the noise is outside now, in a small enclosure. Only the central vac pipe comes through the wall. I have each motor on a separate switch and circuit. Just plug the hose into the central vac outlet and hit both switches.
I have no filter on the vac motor on top of the cyclone, and I had to take the motor off once and have it taken apart at the vac shop. It was a $350.00 motor they told me, and they have a special press to take it apart and put it back together, so now I'm more careful not to **** up any little strips of plastic bags or insulation. That's what got stuck in the motor and screwed it up. Other than that, been using it for a couple years now.