I had this pegged as 40's or early 50's but since taking a closer look at the parts diagrams I now think this is earlier. The reserve cap moved to the threaded pump knob sometime between 1930 & 1934 so my current estimate is 1930's to 40's.
I've revised this slightly again. Looking through the catalogues with Bryan Miller tonight I came across a copy of a 1930 catalogue I forgot I had. It shows the reserve boss & hex reserve cap on the picture BUT parts diagram shows the round pump mounted cap. So - still the same date range (30-40's) as stated but it could be early as 1930 - pending more info.
