Excellent! I really think that, from a practical and engineering point of view, this Optimus design is the best of all of the external NRV systems. Mechanically very rigid, easy to service and that huge pump capacity! This external-NRV should date the stove to c.1915 or earlier, are there any more precise clues? And the designation 'SPECIAL No.1', I wonder what the reason for that was?
It's true it is easier to service NRV . Pump stroke is 13,5 cm so 5 strokes and you have a good fire. This stove has a very small burner outer cap diameter only 39,0 mm
Lovely old stove Thumper. With the external NRV, that style of filler cap and pressure release, the relatively small priming cup, the protruding pump tube and small pump knob, also the fact that it has a bottom stamping, I would date it somewhere between 1915 and 1920.
Dating and the 'No.1 Special' designation: this model seems to appear in one of the 1912 catalogues, but not in any others. The standard No.1 is weighed in at 1.05kg, the newly introduced 1S at 0.96kg, and the 'No.1 Special' at only 0.95kg. The difference being a result of the fact that that the 'Special' is listed as using a No.0 size burner. In subsequent catalogues this variant of the No.1 is referred to a the '1J'. @Thumper In this case is the silent burner that is fitted a No.4 size? - that would share the same thread as an original No.0 burner.
Ian, it is good that you are revisiting the threads of theses old Optimus stoves. I presume that it is all part of your investigations into some of your recent old stove acquisitions. Since this thread was posted we have had eight early Optimus catalogues posted giving lots more information to help date these early stoves.
@igh371 I meas ured my Optimus Special no 1 burner thread and it is smaller than " normal " burner thread. It is only 12,94 mm if the " normal " is 14,50. Also 17 mm key fits the burner .
@Thumper glad to know it checks out - exactly what one would hope to find from the data in that 1912 catalogue So the original burner would have been a roarer of the size normally found on the likes of an '0'/'00'/210 stove.
