The Mercier Valor was a design patented and manufactured by Novitas Fabrik Elektrischer Apparate A.G. of Zürich, Switzerland in 1932. Its Swiss origins are not so strange - Mercier was based in St Étienne, which is as close to Zurich as it is to Paris.

It is a simple, robust, touring (rather than racing) design. The cable pull rotates a drum with a spiral surface cut into its inside surface. This spiral acts on a bolt head screwed into the main rod that holds the pulley cage, moving it in and out as the drum rotates. All this is very reminiscent of the contemporary Cyclo designs. However, unlike the double cable, unsprung Cyclo, Mercier opted for a single cable with a spring in the derailleur. This spring pulls the guide pulley outwards - making the derailleur top normal. The derailleur also has rather well shielded moving parts - meaning that the grease was likely to stay in, and the mud was likely to stay out.

I believe that the Mercier Valor went through a number of development stages:

• The initial generation (1934?) had an external pulley cage spring that led from the tension pulley bolt to a fixing on the rear dropout. Initially the pulley cage arm was short (55mm centre to centre) and the tension pulley had large (60mm) flanges. I believe that these versions were initially branded 'Valor', but that this was soon changed to 'Mercier'.
• A second generation (1937?) was largely identical - but had a longer (70mm) pulley cage arm.
• A third generation (1938?) moved the pulley cage spring so that it led from an eyelet at the top of the pulley cage arm, along the chainstay to a clip. The tension pulley was also reduced in size to 50mm diameter. Finally this generation was available with either a steel or an aluminium pulley cage arm.

These dates are a touch spurious. The 1932 date of the founding patent is not in doubt. The 1934 date for the appearance of the first production derailleurs comes from The Dancing Chain. I have some adverts from 1936 also showing this first generation. And at that point my hard data really stops. If you have any 1930s Mercier catalogues which have real detail, I would be very interested!

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I think this is an, extremely high mileage, example of a mid-period Mercier Valor, from the second generation described above. Some key features are:

• The pulley cage spring attaches to the tension pulley bolt.
• The pulley cage arm is steel and 71mm centre to centre.
• The tension pulley flanges are 45mm in diameter, but look to have been manually cut down from 60mm.
• The tension pulley is labelled 'MERCIER BREVETÉ S.G.D.G.'.
• The mounting hole for the cable nipple is somewhat rectangular.
• One of the mounting bolts used to attach the derailleur to the frame is probably not original.

The teeth on the hardened steel guide pulley of this derailleur are spectacularly worn - indicating that it has probably given tens of thousands of miles of service. Despite this, the spiral actuation mechanism is still impressively effective.

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• Derailleur brands: Mercier manufactured by Novitas Fabrik Elektrischer Apparate A.G.
• Country: France, manufactured in Switzerland
• Date of introduction: 1936?
• Date of this example: unknown
• Model no.: unknown
• Weight: 357g including mounting bolts and pulley cage spring
• Maximum cog: unknown
• Total capacity: unknown
• Pulley centre to centre: 55mm
• Index compatibility: friction
• Chain width: 1/8”?
• Logic: top normal
• B pivot: none
• P pivot: sprung
• Materials: mainly steel with some brass small parts and an aluminium tension pulley