“Saving Space with the Liquid Spring” — Product Engineering article (17 August 1959)

In this document

This article from the American magazine Product Engineering (17 August 1959), signed by Lloyd M. Polentz, an engineering consultant in Whittier (California), is dedicated to “liquid springs”: their principle, their advantages, their limitations, and their industrial future pp. 5-7.

Principle and operation

The liquid spring operates through the compressibility of the contained fluid: “Any liquid spring... operates from compressibility of the contained fluid” p. 5. The article describes several variants: the direct compression type, the “tension” type, the “long-stroke” type with a hollow rod (stroke up to 5 feet), and the “compound spring” with a dual spring rate, whose operation (primary then secondary chamber) is detailed with a load/stroke curve p. 6.

Technical problems solved

The article discusses sealing, ensured by the “unsupported-area seal” developed by P. W. Bridgeman (Harvard), allowing thousands of cycles without fluid loss p. 6. It also addresses thermal stability: a temperature variation modifies the preload but not the slope of the load-deflection curve, as compressibility remains constant p. 6.

Numerical sizing example

For a load of 50,000 lb and a stroke of 5 in., with a pressure of 50,000 psi and a compressibility of 18%, the article calculates a cylinder of 1.8 in. (inner diameter) x 3 in. (outer diameter) x 8.6 in., for a total length of 17 in. p. 7.

The comparative table “Performance of Four Typical Spring Types” p. 7 positions the liquid spring as the most compact for high loads, but also the most expensive (“Relative cost: high”).

Perspectives mentioned

The article mentions established use in aviation (landing gear) and cites automotive tests: “Automobiles have been operated experimentally for periods of over five years with the conventional leaf springs replaced by small liquid springs” p. 7, highlighting that a single dual-rate liquid spring could replace the spring, overload spring, and shock absorber.

Context

This article appeared in 1959, at a time when Citroën, under the leadership of Paul Magès, was developing the hydropneumatic suspension of the DS (launched in 1955). Pressurized fluids as a suspension principle were of interest to several American manufacturers and suppliers at the time, particularly regarding the “Hydra-Springs” from the Wales company and Tayco devices (Paul H. Taylor).

This document mentions neither Citroën nor the DS: these elements are solely part of the general historical context, external to the archive itself.

Archivist's view

This technical press clipping seems to have been kept by Magès as a documentary watch on solutions competing with or complementary to his own suspension. The numerical sizing example p. 7 and the comparative table of springs p. 7 offer a precise basis for comparison, likely useful for his own calculations.

This document is part of a larger set of his documentation on liquid springs, notably the Wales “Hydra Springs” bulletins and the correspondence with Tayco Developments. It seems to have informed, a few years later, his own comparisons between gas springs and liquid springs, as found in his note of 6 March 1961.