A hard nut to crack.
When I first went to the Hoover Historical Center in August/September of 1980, Stacy Krammes, gave me a series of black and white glossies. One of those was the picture posted above of the non electrics. She also gave me descriptions of various machines which included the Whirlwind and the Agan. For years I took this a factual information, but have since come to learn it was completely incorrect. According to Hoover, the Agan was manufactured by Whitehead and Hoag in Newark, New Jersey, only months after Mc'Gaffy's Whirlwind and the name was not based on that of F. W. Agan, both were completely separate. Unfortunately, I have never been able to figure out what Whitehead and Hoag had to do with the earliest of vacuum cleaners, as they were a company which made buttons. What is correct is that it WAS the second vacuum cleaner introduced.
Sometime after 1875, vacuum cleaners were a dime a dozen with everybody jumping on the band-wagon with new ideas. The first of the tank styles was the Hercules manufactured in Rochester, New York by the father and son team of Peck and Peck, but again I haven't found any documentation other that the patent dates. It seems that like Mc'Gaffy, these were all a design conjured up in some basement, but quickly died on the vine.
As for the Hoover company, they were not in the business of research, the person who wrote the documentation took the data, which was hopelessly incorrect and printed it. If any of the historians here at Vacuumland can figure out exactly who produced the Agan, let me know, I'd love to get he answer to that one.