Magès' supplementary note on spool overlap (10 November 1959)

In this document

This handwritten sheet, signed Magès and dated 10 November 1959, extends a reflection on the "overlap" of hydraulic spools — a subject already addressed in a previous presentation not included here.

Forgotten factors

The author points out that the previous presentation only took into account the difference between two dimensions, L and l, to define the overlap. However, other factors intervene in practice: the clearances between the spool and its bore, the more or less blunted shape of the edges of the grooves or holes, and metal wear due to erosion in the flow zone p. 40.

Three proposed solutions

To solve this problem, Magès presents three assemblies, illustrated by sketches:

• Fig. 3: the intake and exhaust ports are drilled at such a distance that hole A of the spool, by orienting it angularly, can occupy "an infinite number of positions" providing overlap dimensions e adapted to requirements p. 40.
• Fig. 4: a groove of variable width on the spool itself, with dimensions e on either side.
• Fig. 5: a groove of variable width directly in the bore.

In all three cases, the adjustment of the overlap is done by angular orientation of the spool, which is then fixed "by any appropriate means" p. 40.

Context

The spool is a cylindrical sliding or pivoting part which, in the Citroën hydraulic circuits of the time (correctors, regulators, suspension valves), controls the passage of fluid according to its position. The fine adjustment of these clearances and overlaps is decisive for the precision and reliability of the hydropneumatic systems developed around the DS.

This note is likely part of the ongoing work carried out by Magès and his team at the Hydraulic Laboratory on the reliability of the DS hydraulic components at the end of the 1950s — a period when other documents in the same file attest to similar concerns regarding the quality and wear of components.

Archivist's perspective

This "supplementary note" clearly illustrates Magès' working method: revisiting a theoretical reasoning already presented to integrate the real imperfections of manufacturing — clearances, wear, blunted edges — which no simple formula can anticipate p. 40.

The choice of three equivalent solutions (fig. 3, 4, 5), all based on an adjustment by angular orientation of the spool, testifies to an engineer's approach seeking the simplest solution to industrialise rather than the most sophisticated.

It seems that this sheet follows a broader presentation on spool overlap, not preserved in this selection, but its classification in the folder "Hydraulic components" confirms its connection to the overall work on the DS hydraulic components carried out during the same period, as evidenced by the DS HP pump tests carried out a year earlier.