Montblanc's 'pneumatic' pump-filler was developed as an alternative to lever-filling systems, which tended to create areas of weakness in the barrel where the shaft was pierced to take the lever. A patent was granted on 28 March 1923 and the pen was produced from 1924-29, although it was not mentioned in the catalogues of the time, and is believed to have been sold mainly in France and Scandinavia. Most examples have the vent-hole in the end of the plunger cover (see lot 256), however it is less well known that an alternative version was manufactured with a two-piece plunger-cover where the end-disc (and not the user's thumb) covers the vent hole which allows air to escape from the sleeve thereby causing the sac to expand and fill the pen. These models carry the COMPRESSOR imprint. A mottled hard rubber example is illustrated in Rösler, but none in red hard rubber, which was rarely used in early Montblanc pens.
This is a unique opportunity to acquire a technically fascinating and extraordinarily rare model from the period summarised by Anne-Marie Rösler as an era when 'Simplo's engineers and sales staff were simply bubbling over with ideas and energy'.