You have an example of the Blackmer Rotary pump. They started making them in 1903. These pumps were used to pump both gasoline and oils, even paint and varnish. They were also used to pump water from underground gas tanks.
I have a 1928 Blackmer catalog, and none of them have a meter on them, so I would say your pump was made after that date.
Without looking this up, I believe I remember that Blackmer also made pumps for visible pumps.
My catalog shows about 50 Rotary pumps, but only five of them are small, most are large commercial pumps.
One more thing, in 1931 Blackmer pumps were used by the U.S. Government at Wright Field and the Fairfield Depot, outside Dayton, to fuel all the 672 Army planes parked there.
Author, Gas Pump Identfication books 1st & 2nd Editions & Air Meter Identification books
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