Internal memo from Paul Magès (1 March 1957) on the failure of 'Dowty' seals

In this document

This internal memo, dated 1 March 1957, is addressed by Paul Magès to Mr. Delerive, with copies to Messrs. Cadiou and Thaon, under the B.E.A reference "11 196" p. 210.

The history of the problem

Magès recalls that "at the origin of hydraulics on cars", Citroën had to solve "a multiple seal problem", settled by "O-rings embedded in sheet metal plates" p. 210.

The DOWTY solution

The supplier Dowty had then proposed an alternative solution: seals "moulded directly into the plate, with the rubber adhering to the metal" p. 210. A pre-production series was produced and fitted to Citroën prototypes "without any difficulty", with tests revealing "nothing abnormal" p. 210. Magès stresses that this initial confidence was based on the experience of Dowty, "which worked in this branch long before us" p. 210, comparing the situation to "not giving advice to SKF for the production of ball bearings" p. 210.

The failure and the reversal

Subsequently, Dowty proposed modifications to its solution, which Citroën trusted. These modifications proved to be "catastrophic", forcing Citroën to return to "our initial solution" p. 210, i.e., the original O-rings.

Context

This document is situated within the framework of the development of the hydropneumatic suspension, a flagship system invented by Paul Magès and launched on the Citroën DS in 1955. The issue of the sealing of hydraulic circuits—subjected to high pressures—constituted a major technical challenge for the reliability of this revolutionary system.

Dowty was a recognised British supplier, specialising in particular in hydraulic equipment for aeronautics, which explains Magès's reference to its prior expertise in this field.

Archivist's perspective

This note illustrates, with a certain irony assumed by Magès, an episode of industrial management where the trust placed in an expert supplier turned against the company. The tone is clear, almost pedagogical in the explanation given to his management: Magès justifies a posteriori a decision (trusting Dowty) and then the reversal that it made necessary.

The document is probably part of the logical sequence of work carried out on seals since the beginnings of hydropneumatics, traces of which can be found as early as the 1940s in the same file, such as the plans for hydropneumatic suspension with differential interaction. It testifies to the rigour with which Magès documented, even technical failures, the engineering choices that shaped the final reliability of the DS system.

This piece naturally finds its place in the summary of folder 41-59, devoted to the technical evolution of the hydropneumatic suspension.