You can make a Dual 50 Renovator work on a Sanitronic 7 or older single speed machine, simply by drilling a hole in the center of the Rug Renovator head and screw a screw in there so it comes in contact with the safety switch. This was done to my parents 518 KIrby when the Rug Renovator came out in 1965, I remember them having a Rug renovator on their Kirby and in later years I discovered that a screw was drilled into the back of the head, its not original, but it worked.