Request to the Laboratory for a pre-production run of 100 DS HP pumps (25 November 1958)

In this document

This André Citroën Laboratory sheet (53, rue Balard, Paris) bears the test number 224 878 and is dated 25 November 1958 (registration stamp "28 NOV. 1958"). It is addressed to "Mr. INGUENEAU", a mention to which a handwritten annotation "M. Magès" is added.

Purpose of the request

The document concerns the 7-piston HP pump of the DS. It indicates that "tests on a pump fitted with a clearance between pistons and liners of 0.002 show a clear improvement in the flow coefficient at 90° compared to pumps fitted with the series clearance" p. 19.

Requested pre-production run

On this basis, the Laboratory requests the launch of a pre-production run of 100 pumps with "a clearance between piston and liner of between 2 and 4 µ (as close as possible to 2 µ)", these pumps being required to "pass through the Asnières Hydraulic Lab" p. 19. The stated goal is to carry out "flow measurements and endurance tests" p. 19.

The document specifies that flow curves Q = f(θ) for clearances of 2, 3 and 6 µ are attached to the note p. 19.

The page also bears two unidentified handwritten signatures, a "P.J." (enclosure) mention and a "µP" annotation at the bottom of the page p. 19.

Context

The DS, introduced in 1955, is the first mass-produced automobile equipped with a hydropneumatic suspension designed in particular under the direction of Paul Magès, who joined Citroën in August 1925 and spent his entire career there, from technical writer to deputy head of Super-Control, until his retirement in September 1974 (Draft letter from Paul Magès to Mr. Sarre and interview plan of 11 May 1969). The DS hydraulic system relies on a high-pressure pump supplying all circuits (suspension, steering, brakes).

Adjusting the clearance between pistons and liners in a piston pump is a classic parameter for optimizing volumetric efficiency: too wide a clearance encourages internal leaks, too tight a clearance risks seizing. The micron (µ) is the usual unit for this type of precision mechanical tolerance.

Archivist's perspective

This document illustrates the continuous optimization work carried out on the DS HP pump after it entered production, several years after the model's launch. It testifies to an iterative engineering approach: observation of improvement in a limited test, then a decision to validate this gain on a larger scale via a pre-production run of 100 units, before a possible general rollout in series production p. 19.

It is likely part of the continuity of the tests mentioned in the DS HP pump flow curves of November 1958, and could be compared with the DS HP pump drawing no. E 401.8444 from the same period, these three pieces likely belonging to the same test campaign.

The presence of the handwritten mention "M. Magès" suggests that this request was forwarded to him or that he was a recipient, without the document allowing us to say more about his precise role in this matter.