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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison of the design and operation of French and American shock absorber instruments.

Identifier  ExFiles\Box 25\2\  Scan130
Date  31th January 1927 guessed
  
Mr. Maurice Olley.

-2-

Inasmuch as all air or gas must rise to the top of the instrument, we gain several advantages by our construction:

Elimination of all air as desired.

Separates dense fluid from fluid which might be mixed with air.

Rapidly replenishing of the working chamber.

A horizontal wing is used in the French instrument and flange is provided with a vent. It is impossible to vent the air from the work-ing chamber as this allows the fluid to mix up more or less and, after the instruments have run a very short distance, the efficiency is probably reduced one-half. The fluid which then emulsifies is forced into the replenishing chamber and under certain conditions might build up a pressure.

In the American built instrument we place the air vent about 4/5 from the bottom. In this way the upper portion of the working chamber forms an air pocket or cushion which softens the checking effect which par-ticularly shows to advantage on boulevard riding. It also produces in the instrument, what might be called, a neutral point which allows the movement of the lever a small amount in either direction without setting up any considerable resistance.

In the American instrument we control the ball movement in the wing which, on rapid movement of fluid, produces a counter resistance making the shock absorber double acting. This permits softer springs to be used on a car.

The flange construction which is used to form the working chamber separates it from the replenishing chamber.

In the American instrument we use two ball valves in the flange. The French instrument uses three and also a ball valve in the vent.

The construction of the vent in the French instrument is so large that a considerable part of the fluid can be forced thru it at times and will not replenish rapidly enough.

The regulating valve in the American instrument differs entirely from those used in the French instrument. We use a needle metering valve which permits about 80% more range for adjustment. The resistance is controlled more accurately thru the wider range. We also add 15% alcohol to the glycerine which brings the freezing point about 50° Fahrenheit below zero and temperature change in viscosity of the fluid is reduced about 50%.
  
  


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