The models were designed following an article from the Kansas State Agricultural College Bulletin – Volume IX April 1, 1925 Number 3
Comparative Tests of Automatic Ventilators – This was a test of automatic ventilators which the test divided into four classes – plain stationary, stationary siphoning, plain rotary, and rotary siphoning. From page 14, I used the Type 1A and 2A plain stationery for my models. Pages 18 and 19 has dimensions of the ventilators and diagrams.
While I designed my models for O scale I presume that they can be used in other scales. The full-size ventilators are only 17 in. dia. In HO this would be 30 in. dia.