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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).
List of alterations for a 10,000-mile relay test on 12-EX, including governor and piston modifications.

Identifier  WestWitteringFiles\O\2April1926-June1926\  Scan032
Date  4th April 1926 guessed
  
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-4-

10,000 miles test in duralumin.

The relay that we have fitted up on 12-EX for the next 10,000 miles test has the following alterations:

(1) Aluminium governor weights. Half the mass of the original steel weights.

(2) Duralumin small inner relay piston.

(3) Improved arrangement of leather and ring, large relay piston.

(4) 7º initial advance on relay obtained by dropping floor of chamber .100". (Neck of governor rod already as close as possible to small piston).

[Diagram showing a mechanical part with an arrow pointing to a section labelled 'Floor dropped .100"']

(5) Return spring over relay 12 lbs. in retard position as at present.

(6) Present standard magneto with sleeve friction 2½ lbs. and light return spring.

The resulting advance curve with oil pressure of 10 - 15 lbs/sq.in. at 60°C is shewn in Graph 11.

The disadvantage of using light governor weights is the fact that they suffer when the oil is cold and the viscosity affects the small inner piston. We should prefer using stronger control springs and the present governor weights.

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