Wales Hydra News No. 5: an Hydra Spring for an explosive military device

In this document

This issue No. 5 of the Wales Hydra News bulletin presents a military application of the 875 series Hydra Spring, integrated into the piston of an "explosive military device" p. 21.

The technical problem

The text explains that the military application required energy absorption to prevent structural failure under impact shock. The bulletin compares the situation to "firing a shell and catching it before it leaves the gun" p. 21. The Hydra Spring was designed to be integrated into the piston (the shell) of the explosive device.

Announced performance

According to the bulletin, the addition of the spring represented only 6 extra ounces for an energy absorption calculated — via handwritten corrections — at *20,000 lbs in a spring developing a force of 28,000 lbs, operating in 16 milliseconds p. 21. A note specifies that these values were modified by hand ("15,000" crossed out replaced by "20,000", "23,000" crossed out replaced by "28,000"), without it being known whether this correction came from the manufacturer or a reader p. 21.

The bulletin also mentions that after a successful operation, the client ("contractor") requested more energy absorption as a safety factor, obtained by adding Comproil (Wales oil) p. 21. The device was only deemed satisfactory after the inclusion of the Hydra Spring p. 21.

Comparison to a coil spring

For comparison, an equivalent coil spring (1.75'' diameter wire, 10'' long, 8.5'' diameter) would weigh 57 lbs and could not function at the high speeds required by this device p. 21.

A graph illustrates the force (up to 28,500 lbs) as a function of the stroke (up to 1.38 inches), with two curves — "ORIGINAL" and "FINAL CURVE" — the area between them representing the stored energy/work p. 21. A photograph shows a cylindrical metal part with a conical end, likely the piston described p. 21.

Context

The American manufacturer Wales-Strippit Corporation marketed compact hydropneumatic springs in the 1950s under the Hydra Spring brand, potential competitors to conventional coil springs for high energy density applications. This period corresponds to the research conducted at Citroën, under the direction of Paul Magès, on the principles of hydropneumatic suspension that would lead to the DS (1955). The military applications mentioned here (shock absorption, explosive systems) remain outside the automotive world but illustrate the general interest in this type of compact and powerful spring at that time.

Archivist's perspective

This bulletin is part of a series that Magès seems to have followed with attention, as evidenced by the previous issues kept in the same collection — see Wales Hydra News No. 4 on the compressibility of Comproil oils, or Hydra News No. 2 on compression springs.

The military example presented here, far removed from the automobile, seems to have interested Magès as a demonstration of principle: the ability of an Hydra Spring to absorb considerable energy in a reduced volume and weight, a challenge directly transposable to vehicle suspension. The handwritten corrections on the force values p. 21 suggest an attentive reading, perhaps a verification or a re-evaluation of the figures announced by the manufacturer.