Comparative viscosity and distillation curves of a silicone versus Lockheed fluid (1949)

In this document

This handwritten sheet on graph paper presents two comparative graphs between a tested silicone and a Lockheed fluid (the reference hydraulic fluid at the time).

Viscosity curve

The first graph shows "Viscosity in centipoises" on the y-axis (values 10, 30, 50) and "Temperature in degrees Centigrade" on the x-axis (10 to 90). Two curves are plotted:

• in a solid line, the "Viscosity curve of the silicone sent";
• in dotted lines, the "Curve of a Lockheed fluid".

The density of the silicone sent is specified: "0.948 at 20°".

Distillation curve

The second graph shows the "Distillation curve of the silicone in % distilled as a function of temperature", with a percentage axis (10%, 30%, 50%, 100%) and a temperature axis ranging from 150° to 400° centigrade p. 3.

A handwritten annotation at the top of the page indicates "1949" p. 3.

Context

Lockheed fluid (a classic glycol-based hydraulic fluid, used notably for brakes) was commonly used as a comparison reference in the post-war automotive industry to evaluate new hydraulic fluids.

Silicones were then beginning to interest engineers for their viscosity stability properties over a wide temperature range — a major issue for any hydraulic system required to operate in both extreme cold and high heat, which is precisely the challenge that the future hydropneumatic suspension of the DS would encounter.

These tests are part of the research conducted at Citroën on hydraulic fluids, prior to the development of the "hydraulic components" that would equip the DS 19 from 1955 onwards. They are chronologically situated after Paul Magès joined the design office and the establishment of his plans for hydropneumatic suspension on 17 February 1944, and after the first tests of the 2 CV with hydropneumatic suspension in May-July 1946 — that is, a decade before the presentation of the DS on 6 October 1955.

Archivist's perspective

This document seems to correspond to a stage of exploratory research on hydraulic fluids, probably conducted by Paul Magès or his team to evaluate silicones as a possible alternative to classic fluids p. 3.

The direct comparison with a Lockheed fluid suggests an issue of substitution or performance improvement as a function of temperature — a crucial question for any automotive hydraulic system.

This document belongs to the same file as the Cover of folder 49.66 "Hydraulic components" and is part of the same chronological context as the Schematic diagram of the DS 19 hydraulic circuit (1949), dated the same year. It likely illustrates the preparatory work carried out in parallel with the development of the mechanical components of the future hydropneumatic suspension.