Paul Magès note: DS improvement programme – HP pump and pressure regulator (10 December 1958)

In this document

This two-page service note, written by Paul Magès on 10 December 1958 (referenced B.E.A. No. 11 893), is addressed to a list of engineers (Ingueneau-Bertrand, Hartmann, Louis, Caneau, Fleury, Pompon-Chalard, Jollivet-Gobilliard) with copies to Messrs. Cadiou, Guyetant and Sabrazat. It details a technical improvement programme for the DS high-pressure pump and pressure regulator, point by point from a) to h).

HP pump: sealing and wear

The installation of seals between liners and bodies allows for "recovering the normal pump flow at low speeds and when hot" p. 264. Magès requests the rapid application of a central nut to flatten the cylinder head and avoid deformation of the aluminium bodies p. 264, as well as the creation of "expansion grooves" around the liner housings to contain any potential seepage p. 264.

Reduction of clearances and material quality

Based on a "LABO. Report No. 224 878 of 25.11.58" p. 264, the note recommends tightening operating clearances from 3-6 microns to 2-4 microns, gradually, to reduce wear due to erosion p. 264. The attention of metallurgists is drawn to "chipped valve seats" in the cast iron of the liners p. 264.

Swashplate bearing and pump shaft

Magès deems the manufacturing means "insufficient to ensure the quality of this bearing" p. 264-265 and requests reinforced monitoring of the inspection at each stage, as well as an inspection of the material and treatment p. 265. Regarding the pump shaft (reference D 321.14a) and the upper plate D 391.85, surface hardening is required to avoid the formation of a chip during assembly, a question raised by Mr. Masseron to Mr. Gobilliard p. 265.

Pressure regulator

The reinforcement of the pressure regulator, already requested by notes E. 30 707 (13/11/57) and 31 822 (12/5/58), is demanded "rapidly": modification of the two-hole liner, guidance of the small ball (cage), and removal of the piston seal to improve sensitivity and limit "sluggish operation" p. 265.

Context

The DS, introduced in 1955, features a hydropneumatic suspension controlled by a hydraulic unit combining a high-pressure pump and a pressure regulator — a system then unprecedented in the automotive industry, developed by Paul Magès at Citroën. The very first years of DS production are known to have revealed several mechanical weaknesses in this innovative hydraulic system, requiring continuous reliability improvement campaigns.

Archivist's perspective

This document illustrates the industrial development work that follows the introduction of a major innovation: it is not a matter of initial design here but of correcting failures observed in service or during testing, three years after the launch of the DS. Magès' tone, precise and directive, reveals a constant concern for reliability and a rigorous method — he relies on dated laboratory reports and precise previous notes p. 265.

The reference to notes from 1957 and 1958 not yet applied suggests probable tensions between the design office and manufacturing, a theme found in other documents in the same file, such as the Manufacturing schedules 1945 or the Summary of folder 41-59, which document more broadly the technical evolutions of the hydropneumatic suspension and the DS.