Citroën letter to the Mines Department (12 March 1953) regarding the hydropneumatic accumulator

In this document

This is a letter dated 12 March 1953, addressed by Citroën to the General Engineer of Mines, Head of the Mineralogical District of Paris, 40 avenue d'Iéna p. 2.

Purpose of the letter

Citroën announces plans for "the construction, in large series" of a device, attaching to this letter "the descriptive statement, the calculation note and the plan" p. 2 — three documents that are likely found in the same archive file.

The technical question raised

After studying the "General Regulations for Gas Pressure Appliances (1943)", Citroën asks the administration about a specific calculation point: for the characteristic figure PV = 80, should one count "the total volume of the accumulator (air + oil)" or only "the volume of air limited by the synthetic rubber membrane and the upper hemisphere" p. 2?

The company also anticipates the case where the administration might deem the stricter conditions corresponding to a ratio "PV > 80" applicable: it then asks if a derogation is possible, and in what form p. 2.

Material elements

The page bears a handwritten date "12-03-53" and the underlined handwritten mention "M. Magès", at the top left, as well as an illegible signature at the bottom of the page. The background of the page reveals, in overprint, fragments of another sheet ("DESCRIPTIVE STATEMENT", "accumulator", "hemisphere"), which suggests the physical proximity of the letter to the technical document it accompanies.

Context

This letter is part of the context of the development of the hydropneumatic suspension designed by Paul Magès for Citroën — who joined Citroën in August 1925 and was then deputy head of the Super-Control (autobiographical notes) —, a system that would notably equip the future DS presented on 6 October 1955. The sphere accumulator, filled with compressed nitrogen and separated from the oil by a membrane, is one of the key components of this device, the plans for which date back to 17 February 1944 (hydropneumatic suspension plans).

The mentioned regulation, relating to gas pressure appliances, falls under the French regulations on pressure vessels, placed under the control of the Mines service — hence Citroën's approach to secure the regulatory compliance of its new accumulator before its mass production.

Archivist's perspective

This letter illustrates an administrative and regulatory stage in the development of the hydropneumatic accumulator, prior to its industrial production. It testifies to Citroën's concern to have a technical calculation point validated by the Mines administration before any mass production launch.

The handwritten mention "M. Magès" p. 2 confirms that Paul Magès was directly involved in the follow-up of this file, consistent with his role as the inventor of the system.

The document likely refers to the Regulatory descriptive statement of the Citroën hydropneumatic sphere and the Calculation note for the wall thickness of the accumulator, cited as attachments p. 2, which would allow for a better understanding of the question posed to the administration.