E.L. Malvaney submitted a Word of the Week request, emailing me a photo along with the text below saying,
“…I think this would be a fine WOTW, especially since we have at least two fairly recent examples of the ventilators on MissPres, including Knox Glass Company [and the GE Lamp and Glass Works]…”
After some research I found that these are refered to as natural draft roof ventilators, gravity ventilators, monitor ventilators or more specifically Robertson Monitor Ventilators. I don’t know when the two corresponding clam-shell elements were first debuted in an industrial process, but it’s likely sometime between the late 1920’s and the late 1930’s I believe, due to the photographic evidence I have seen. I identified some patents ,  from the 1960s for improvements to the design but I have not yet found a patent implementing the original design.
These types of vents are used in steel mills, glass factories, or anything with a really hot oven. When you need to evacuate the surplus of thermal energy generated by the oven, at the hot end of the factory you need to do so carefully or the draft created could wreak havoc on the industrial process you’re conducting. Essentially the whole roof of the building is opening up when the vent is open. Natural draft or gravity ventilators refer to the fact that no fans or blowers are used in the ventilator.
The vent opening in the roof of the building is sized to the amount of gas that is to be exhausted. Proper venting is important in glass manufacturing because, if not done correctly, it might create air currents in the cold end of the factory that could stir up dust on the still cooling glass, affecting the quality of the product.
In New York the Owens Corning Glass Museum‘s contemporary gallery features a “renovated ventilator building, which houses a 500-seat hot glassblowing demonstration venue.” I think this just shows how integral and visually associated with the glass production process the gravity ventilator has become.
If you have a construction or preservation word you’d like to see defined, just leave a comment below, or drop an email line to thomasrosell at misspreservation.com.