Magès note: numerical comparison of the DS gas spring and the Tayco liquid spring (6 March 1961)
Faced with the Tayco proposal, Paul Magès calculates that a liquid spring equivalent to the DS gas spring would require 32 litres of oil compared to 0.750 litres — and concludes that the solution is of no interest.
Understanding this document
In this document
This two-page typewritten note is explicitly written "Following TAYCO proposal (12.12.1960) TAYLOR DEVICES" p. 27 and signed "Mr MAGES 6/3/61" p. 28, which confirms and specifies the dating to the day.
The comparison calculation
Magès starts from the DS 19 gas spring: a 750 cm³ sphere inflated to 60 kg/cm², used at a pressure of 100 kg/cm². For a 10% load variation (pressure from 100 to 110 kg/cm²), the gas volume must vary by 40 cm³ p. 27.
He then transposes this same volume displacement to a liquid spring, relying on the bulk modulus of a special oil (Comproil 118 oil, cited with its source "Hydra Spring Division Wales-Strippit Co North Tonawanda NY - document 1955"), set at 8000 kg/cm² p. 27.
The result of the calculation:
| System | Required volume | Operating pressure | Page |
|---|---|---|---|
| Gas spring (DS) | 0.750 litre | 100 kg/cm² | p. 27-28 |
| Equivalent liquid spring | 32 litres | 100 kg/cm² | p. 28 |
| Liquid spring (doubled pressure) | 8 litres | 200 kg/cm² | p. 28 |
| Hydropneumatic suspension (Citroën tests) | 3 litres/wheel | 150 kg/cm² | p. 28 |
| Air spring only | 9 litres (≈400 mm Ø) | 5 kg/cm² | p. 28 |
Magès' conclusions
He judges the pure "liquid" solution "not reasonable", "not even for a truck" p. 28. He concludes that for a good suspension one needs "great flexibility" and that one must "use high-pressure gas to reduce the volume" p. 28, the hydropneumatic path remaining in his view the only conceivable one for a high-pressure gas suspension "for the moment" p. 28.
A final note recalls that "DOWTY has had liquid suspension patents since at least 1946" by citing French patents 931.110 and 931.111 p. 28.
Context
The Tayco proposal mentioned refers to the letter from Paul H. Taylor (Tayco Developments) to Citroën dated 12 December 1960, which presented a "Liquid Spring" system competing with the Citroën hydropneumatic suspension. The DS, launched in 1955, already used pressurized gas spheres developed by Magès and his team.
Archivist's perspective
This document illustrates, it seems, Magès' working method: faced with an external technical proposal, he produces a rigorous and numerical counter-calculation rather than an objection of principle, to demonstrate through numbers the practical inferiority of a competing solution p. 27-28.
The explicit reference to the Wales-Strippit and Dowty documents shows that Magès followed and compiled an extensive technical watch on liquid springs, as evidenced by other items in the same file, notably the Wales "Hydra Springs" bulletin and the notes on the Dowty suspension. This note probably constitutes the fair copy of the handwritten drafts on the same subject.
In the same folder
Dating
6 March 1961
Document
2 pages
Source: « Scanner 5 août 2025 à 14.37.pdf », p. 27–28
Category
Archival note
P.27 page 1 of the note ("Following TAYCO proposal (12.12.1960)"), p.28 "- 2 -" with date 6/3/61 and Magès signature.