Optimus didn't use any date code, so you can't get a year by that stamp. Possibly a period if the design of the stamp varied over the years. I'm sure someone else know better when it comes to that bit.
@Firedevil can we tell "the year"? as in a specific year... most often no. In very broad terms it is somewhere 1910-1940. We can provide a more narrow year range after considering *all the details. Several fellow stovies have made progress w/early Optimus dating. if yours is just a web image, myself, i may pass on your inquiry, sorry. If you have the stove in-hand (do you?) and *you provide more detailed images, I WILL be glad to assist with a more narrow year range as hobby time allows.
It's certainly burning well! The pump know has a very reddish copper hue to it, looks like it has been left in a vinegar bath for too long at some point and some of the zinc has leached out? The experts will be along soon, but the fact this is a version marketed for the Vacuum Oil Company may help narrow things down a bit.... Have a look at this similar example belonging to @igh371
THANK YOU with comparisons I've done here , so far, it seems to me your Optimus 1S, for Vacuum Oil, dates from 1920s (1921-on, and i doubt it is later than '29)
Sunflower No. 1 ↑ Some corrections: 1931 the name Vacuum Oil Company changed to Socony Vacuum Corporation. 1934 Change to Socony-Vacuum Oil. 1955 Change to Socony-Mobil Oil Inc. 1966 Change to Mobil Oil Corporation. This would mean the stove is pre 1931, if the name Sunflower disappeared 1931 completely. But there was a German/Austrian branch at least until 1938 named Vacuum Oil AG in Vienna. Radler So it looks like the Sunflower brand and name might have disappeared by 1931. Best Regards, Kerophile.
