Note on the safety of the hydraulic unit (12 March 1953)

In this document

An argumentative note for the Mines department

Dated 12 March 1953, this three-page typewritten note is addressed to the Mines department to discuss the regulations applicable to a hydraulic unit intended to equip cars "for various applications" p. 1. The author—likely Paul Magès, who joined the Citroën design office in the late 1930s and worked from 1944 on the hydropneumatic suspension plans (Hydropneumatic suspension plans with differential interaction)—insists on the refusal to "risk a malfunction" and on the desire to follow the Mines department's data for the calculation of pressure accumulators p. 1.

The calculation of the accumulator

The example given is that of a 0.75-litre spherical reservoir inflated with air to 100 kg/cm², then brought to 160 kg/cm² by the arrival of the liquid, with a burst pressure exceeding 480 kg/cm² p. 1.

The author argues that a larger reservoir, containing the same volume of air (0.5 l) at 160 kg but supplemented with incompressible liquid, stores "no additional energy" and would therefore remain, in his view, below the regulatory limit p. 2. He asks to be exempted from official stamping and periodic inspections, while accepting "sampling-based control" p. 2.

Comparison of risks and safety devices

The note compares the risk of the accumulator to the bursting of a tyre, the fuel tank, or the wear of steering and braking components p. 2. It finally mentions two planned devices: a hydraulic pressure regulator that automatically cuts the pump at maximum pressure, and a component acting as a safety valve, also designed to avoid unnecessary work for the pump p. 3.

Context

This document is situated at the very beginning of the development of the hydropneumatic suspension at Citroën, whose first plans date from February 1944 (Hydropneumatic suspension plans with differential interaction (17 February 1944)) and the first tests on 2 CV from May to July 1946 (Notebook of the first 2 CV hydropneumatic suspension tests (May-July 1946)), a technology that would equip the future DS presented on 6 October 1955. The "Mines department" then designated the administration in charge of the control of pressure equipment in France, a regulatory framework designed for heavy industry and poorly adapted to small innovative automotive components.

Archivist's perspective

This text sheds light, prior to the market launch, on the regulatory and argumentative dimension of Magès' work: it is not about pure technique here but about negotiation with the administration to have an innovation accepted. It seems that this note was written to anticipate objections before industrialisation, within the broader framework of the development of the hydraulic unit during these years, between the first plans of 1944 and the test of the 15-Six H in April 1954 (Road test of the 15 Six H (ELV 412) by Paul Magès, 3-5 April 1954) which precedes the presentation of the DS p. 1-3. The concern expressed about "not discrediting" Citroën p. 2 testifies to an acute awareness of the image issues linked to this nascent technology.