Both of my Gas Pump Identification books have your answer. Until proven wrong, Guarantee Liquid Measure Pump Company (Fry) introduced the first visible pump around 1917. Of course all the other pump companies took notice, should they start making visible pumps, or should they make a visible attachment that would convert their existing pumps to visible pump? Most companies waited until the early 1920s to decide to make a visible pump, while American, Fleckenstein, Groeken and a couple of others decided to go the visible attachment. Most of these companies made visible attachments that would attach to any other companies curb pumps.
My second edition of the ID book shows about 15-20 curb pumps with visible attachments. While my books are both out of print and also out of stock, you can still purchase a copy of either of the books on Amazon Ebooks. While this is not the best because you cannot go to a certain company to look at a pump, you have to start at the beginning and click a lot of times. If you decide to purchase a copy remember the caption describing the pump is always under the pictures, not above it.
For some reason I received royalties for the printed copies, I do not receive royalties for the E books.
Hopefully the 3rd edition will be out soon.
Jack Sim
Author, 1st & 2nd editions of Gas Pump ID book, 3rd edition is now available at
www.gaspumpbible.comAir Meter ID book also available