Test report no. 220.777: endurance of H suspension cylinder seals

In this document

This is test report no. 220.777 from the André Citroën Laboratory (53, rue Balard, Paris), dated 30 April 1952, with a handwritten note "5 MAY 1952" and an annotation "Mages" in the header p. 109. The document bears the reference No. 329-2-52-CR-5.000 and deals with the endurance of the cylinder seals of the H suspension p. 109.

PVSC car - ELV.280

This car "suddenly emptied of all its LOCKHEED fluid" via the rear right (RR) cylinder seal while driving, without any notable prior leakage while stationary, after 35,000 km covered p. 109. Disassembly revealed a rubber seal "partly torn and partly worn", as well as significant play of the piston in the cylinder and the seal support ring p. 109. The measurements of the piston and cylinder are detailed:

Marks from the link rod next to the bead are observed in the bottom of the piston, possibly explaining the wear of the cylinder and the ring p. 110. The rear left (RL) cylinder of the same car (same mileage), which was not leaking, shows a "slightly damaged" seal and similar bearing traces p. 110. The car was reassembled with two new rubber seals, new K8 end link rods and steel washer centering, as well as a new cylinder, piston and ring on the right p. 110.

PVSC car - ELV.230

Similar but less pronounced incident, occurring while stationary around 34,000 km p. 110. The rear right (RR) cylinder shows a significant leak with a heavily worn seal; the rear left (RL) cylinder a lesser leak with a worn seal, without play between cylinders and pistons p. 110. A note specifies that a previous reassembly, after 20,000 km, had tightened the seals "fully", which may have caused their deterioration; the car was then reassembled with a rubber seal on the right and a nylon seal on the left p. 110.

PVLC car - ELV.368

After 21,000 km, during a change of link rods, a nylon seal showed "a slit on the lip following a generatrix", without any associated significant leak; it was replaced by another nylon seal p. 110.

Context

The hydropneumatic suspension, developed by Paul Magès — who joined Citroën in August 1925 and remained there for 49 years, technical writer then deputy head of the Super-Control (autobiographical notes) —, would equip Citroën cars from 1954-1955: first plans as early as 17 February 1944 (hydropneumatic suspension plans with differential interaction), first 2 CV tests in May-July 1946, test of the 15-Six H in April 1954, then the DS presented on 6 October 1955. The Lockheed fluid, of mineral origin, would later be replaced by the LHS then the LHM, partly for reasons of compatibility with the seals. Endurance tests on rolling vehicles (PVSC, PVLC — probably internal prototype designations) were part of the long development process before industrialisation, here dated April 1952, i.e., two years before the 15-Six H test and three years before the presentation of the DS.

Archivist's perspective

This document concretely illustrates the empirical development work carried out around the H suspension: wear measurements with a micrometer, comparison of seal materials (rubber versus nylon), adjustment of the part-tooling torque (link rods, K8 end) p. 109-110. It constitutes a dated milestone (April 1952) in the chronology of the intensive development of the hydropneumatic suspension, between the 1944 plans and the 1954 tests, and is part of the continuity of the theoretical studies and previous plans kept in the same folder, such as the hydropneumatic suspension plans with differential interaction or the suspension cylinder plan — stroke 100, S = 8 cm². The comparison between rubber and nylon seals, tested here in real conditions, shows the concern for reliability that would shortly precede the commercialisation of the DS.