These photos show the differences between the “large vent” and “small vent” models. The top photo is the before shot from the last restoration of a VMC Pepsi 81by Glen Boyd (MoonDawg). The bottom photo is my large vent VMC Pepsi 81, currently being restored by Glen.
Forgive me for not knowing the correct terminology for the different parts. The small vent model has an approximately 2” diameter tube (red arrow) whereas the large vent model does not have this tube. Also the small vent model has a smaller, more oval-shaped reservoir (green arrow) whereas the large vent model has a larger-fatter, round reservoir.
I have also noticed these differences in the Coke Vendo 81’s. In the photos I have seen, the Vendo V-81A & B models have large vents and the V-81D has small vents. There is an original owners manual for a Coke Vendo 81 (V-81A model?) at
http://www.retroplanet.com/blog/vintage-vending-archives/coca-cola-vendo-81-44-39-soda-machine-service-manuals/. You have to click on the photo to download the manual. Page 27 of this manual shows the “large vent” model configuration. The manual is dated May 1956.
I was just wondering if most of the large vent models of Vendo and VMC 81’s were built between 1955-56 and the small vent models between 1957-59.