Hydra News No. 4 (1954): The compressibility of Comproil oils, annotated by Magès

In this document

This American technical bulletin is titled The Compressibility of Wales Comproils as used in Hydra Springs and Systems, published by the Wales-Strippit Corporation (North Tonawanda, N.Y.), dated © 1954, and constitutes number 4 of the Hydra News series.

The editorial intent

The editorial opens with an ironic remark: faced with readers who object that "textbooks say liquids are incompressible," the bulletin specifies that recent textbooks speak of an "essential" incompressibility, a nuance upon which the entire demonstration rests. Certain liquids, under very high pressures, show more marked compressibility; it is by exploiting this property that Comproils are formulated.

The comparative graph

A graph titled Compressibility Comparison compares four liquids—distilled water, Comproil 62, Comproil 100, Comproil 118—by plotting pressure (up to 20,000 P.S.I.) against the percentage of volume reduction (ΔV/Vo, from 2.0 to 12.0%). A note specifies that each Comproil is designated by its compressibility rate at 20,000 P.S.I.: thus, Comproil 62 is 6.2% compressible under this pressure.

The handwritten annotations

The reader (presumably Magès) added several calculations superimposed on the graph: a formula "dp/K = Δv/v = 0.12, K = 12,000 kg/cm²" with an "instantaneous K = 15,200 kg/cm²" linked by an arrow to a point on the graph; another series "dp/K = Δv/v = 0.04, K = 7,900 kg/cm², instantaneous K → 9,000 kg/cm²"; as well as isolated values "1900 Kg/cm²" and "290 Kg/m² 4.5".

Context

Comproils are oils specially formulated by Wales-Strippit for its liquid spring systems (Hydra Springs), exploiting compressibility artificially increased by compounding—useful in damping or suspension applications where a slightly compressible fluid replaces a mechanical spring.

This "liquid spring" principle was of direct interest to engineers working on hydropneumatic suspension, where the compressibility of nitrogen gas played a role comparable to that sought here with a liquid.

Archivist's perspective

The handwritten annotations suggest that Magès sought to extract from this document bulk modulus (K) values directly comparable to his own calculations on Citroën suspension—a process he would pursue more explicitly in his note comparing gas springs and liquid springs of 1961.

This number 4 is part of a followed collection of the Hydra News journal that Magès seems to have kept and annotated systematically, as evidenced by neighboring issues such as Hydra News No. 3. It likely documents a phase of technical monitoring and comparative calculation, where the engineer sought to situate the performance of Comproil liquids in relation to his own hydraulic requirements.