DS HP pump flow curves — Hydraulic Laboratory tests (November 1958)

In this document

This six-page file gathers the results of tests conducted on the DS high-pressure pump by the Citroën Hydraulic Laboratory in November 1958.

Flow curves according to temperature (6 and 3 micron clearances)

Pages 14 and 15 present curves plotted on graph paper, dated 6 November 1958, measuring the flow rate Q (in litres per 250 pump revolutions) according to the temperature of the CH12 oil, for different piston "settings" (0.7 / 0.8 / 0.9 / 1) and two pressure levels (0 and 175 Kg/cm²).

Page 14 concerns an assembly with a liner-piston clearance of 6 microns, pump speed ≈ 270 rpm; page 15 a clearance of 3 microns, speed ≈ 220 rpm. Both tests specify an assembly "without seal under the liner flange" and an ambient temperature of approximately 20°.

Tests of 19 November 1958 — 2 micron clearance

Pages 16 and 17, produced thirteen days later at the Asnières Hydraulic Lab and signed by Guigné, focus on a pump assembled with a 2 micron clearance and a setting L ≈ 0.8.

Page 16 provides the flow curves as a function of temperature for six pressures (0, 75, 100, 125, 150, 175 Kg/cm²), with three calculated ratios: Q175/Q0 = 0.964 (around 20°), 0.956 (around 60°) and 0.947 (around 90°) p. 16.

Page 17 presents, for the same pump, the flow curves as a function of pressure at a given oil temperature p. 17.

Detailed test sheet (p. 18)

Page 18 is a test sheet no. E 2, dated 19.11.58, concerning a new pump with special clearances. It details, for seven liner-piston pairs numbered 1 to 7, the dimensions φ1 to φ6 and the clearances measured at the beginning and end of the delivery stroke:

(p. 18)

An annotated sketch specifies the "admissible clearance between liner-piston" of 3 to 6 microns p. 18.

Context

The high-pressure pump is one of the central components of the hydropneumatic system designed by Paul Magès for the DS, marketed by Citroën from 1955: it supplies pressure to the circuit that controls the suspension, brakes, and power steering.

The quality and consistency of its flow, regardless of oil temperature and pressure level, are crucial issues for the reliability of the entire system — a flow defect being able to directly affect the vehicle's behaviour. This series of tests is part of the optimisation efforts carried out in the years following the launch of the DS.

Archivist's perspective

This file illustrates the systematic development work carried out at the Hydraulic Laboratory: it seems that the engineers sought, by gradually tightening the liner-piston clearance (6 then 3 then 2 microns between 6 and 19 November 1958), to optimise flow stability in the face of temperature and pressure variations.

The test sheet p. 18, with its precise measurements to the nearest micron on seven examples, suggests a rigorous quality control approach, probably linked to the reliability of the mass-produced pump.

This document is part of a coherent set with the request to the Laboratory for a pre-production run of 100 DS H.P. pumps, dated a few days later (25 November 1958), and with the DS high-pressure pump plan no. E 401.8444, of the same month — suggesting that these tests were preparing for an evolution or a mass-production validation of the pump.