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).
Page detailing the development and various designs of engine valves, including sodium-cooled types.
Identifier | ExFiles\Box 174\2\ img286 | |
Date | 1st September 1931 guessed | |
gressed through a long series of developments, briefly, as follows: Cast-iron valve with steel stem, cast-iron valve reinforced with steel wire, the one-piece steel valve, the same valve with a puddled seat of cast-iron, the nickel-head valve, the tungsten valve, the EWP{Mr Punt} (Electric Welding Products) alloy of low chromium-nickel, cobalt-chrome, Silcrome, CNS (chromium-nickel-silicon), salt and sodium cooling and copper cooling. TABLE | | Sodium | Eutectic | |---|---|---| | Melting point, deg. fahr. | 207.5 | 205-0 | | Boiling point, deg. fahr.* | 1,616 | -- | | Surface tension at fusion temperature, dynes per cm. | 234 | 100† | | Heat of vaporation at b.p., cal.{Mr Calvert} per gm. | 100† | -- | | Specific gravity | 0.97 | 2.2 | * Potassium nitrate decomposes at 750 deg. fahr. † Approximate. will cause heat to be held in the stem and result in expansion and loss of tappet clearance, particularly in L-head engines. A film of oil in the guide aids heat transfer. Fig. 5 shows a valve having a Nicrome shield or shroud spun into the under-side of the head. The lower end is free to move along the stem with expansion. The dead-air space between the valve and the shield acts as an insulator, and the shield prevents the exhaust flame from impinging on the stem. This construction is expensive, but it has merit in some cases. A shroud over the valve guide, as used in Diesel engines to prevent the valve from sticking at the top of the guide, is shown in Fig. 6. The shield is spot-welded and Fig. 3. Fig. 4. Fig. 5. Fig. 6. Fig. 7. COPPER FILLED Fig. 8. Valve-development work is proceeding along two lines. One is to find better steel for exhaust valves, the other, to improve handle, as it reacts violently with water and the reaction is intensified to explosion if pressure is applied. The sodium must be kept under kerosene until ready for use. Before filling, valves are preheated to 700 deg. Fahr. to drive out all moisture and also to create a partial vacuum after the valve is closed and has become cool. Solid sodium is placed in the stem, after * Being a paper recently presented to the Society of Automotive Engineers (U.S.A.). † M.S.A.E.—Chief Engineer, Thompson Products, Inc., Cleveland (U.S.A.). | ||