Specifications D334-07 — Leak and oil pressure tests (15 April 1955)

Citroën specifications D334-07 setting the tolerances for leaks and oil pressure (130-175 kg/cm²) for the hydraulic gear shift and clutch control, dated 15 April 1955.

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Understanding this document

In this document

This typewritten specification, existing in two copies (pages 7 and 8), sets the acceptance criteria for a hydraulic device — presumably the gear shift and clutch control mentioned in the title block on page 8 ("C° HYDRAULIQUE de changement de vitesse et d'embrayage").

Air leak test

Point I° mandates that "no leak [shall be admitted] under 300 gr/cm2 of air between liners, spools or pistons assembled dry" p. 7-8.

Oil pressure tests (130 to 175 kg/cm²)

Point 2° details several configurations to be checked, with the preselector spool D334-33 and the manual clutch control spool D334-30:

Configuration	Clutch cylinder pressure	Gearbox cylinder pressure (start/end)	Page
a) Neutral, auto clutch engaged	49 to 69 kg/cm²	—	p. 7-8
b) Synchronised gear (2nd/3rd/4th)	37 to 48 kg/cm²	21-25 / 31.4-35 kg/cm²	p. 7-8
c) Threshold before gearbox pressure	49 kg/cm² minimum	—	p. 7-8
d) Threshold before drop to 0	49 kg/cm² minimum	—	p. 7-8
e) Pump discharge port supply	1.1 to 1.35 kg/cm²	—	p. 8

These values, initially typed differently, were corrected by hand (crossed out then replaced), with the mention "(m15)" associated with each correction p. 7-8.

Point f), present only on page 8, specifies that by pulling the manual clutch control spool to the maximum, "the pressure […] must drop instantly to 0", and that no pressure must then be recordable by operating the preselector p. 8. The text adds that "no external leak [is] admitted" during the tests, and that the tightening torques of the cover fixing screws and nuts must then be checked p. 8.

The title block on page 8 bears the reference D334-07, the handwritten date "15/4/55", the names "JM" and "VERNEREY", as well as a stamp "55 a 56" and a line of handwritten modifications (m15, m16) p. 8.

Context

This type of technical document corresponds, in the history of Citroën, to the semi-automatic gearbox hydraulic controls developed for the DS, presented on 6 October 1955 — a system where Paul Magès, then in the design office after joining in 1939-1940 (draft letter to Mr. Sarre), played a central role in the hydraulic design. The date of the document (15 April 1955) thus falls between the test of the 15-Six H (April 1954) and the presentation of the DS.

The extreme precision of the tolerances (to the nearest half-kilo) reflects the industrial requirements specific to a mechanism operating at high oil pressure, a technology characteristic of the hydropneumatic engineering developed by Citroën at that time.

Archivist's perspective

These specifications illustrate the rigorous development work that accompanies the birth of a complex hydraulic system: the successive handwritten corrections on the pressure values p. 7-8 testify to empirical adjustments made during the tests, probably in direct connection with the test campaigns conducted by Magès' team.

The common reference D334-07 links this document to other parts of the same technical file, notably the general drawing DS 334-07a of the BB type hydraulic control and the drawing of 25 November 1955 on piston-liner pairing, which shed light on the mechanics targeted by these pressure tests.

It seems that these specifications constitute an essential quality control piece, validating in advance the reliability of a component intended to equip a mass-produced vehicle.