Belpaire firebox
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The Belpaire firebox is a type of firebox used on steam locomotives. It was invented by Alfred Belpaire of Belgium in 1864. Today it generally refers to the shape of the outer shell of the firebox which is approximately flat at the top and square in cross-section, indicated by the longitudinal ridges on the top sides. However, it is the similar square cross-section inner firebox which provides the main advantages of this design i.e. it has a greater surface area at the top of the firebox where the heat is greatest, improving heat transfer and steam production, compared with a round-top shape.
The flat firebox top would make supporting it against pressure more difficult (e.g. by means of girders, or stays) compared to a round-top. However, the use of a similarly shaped square outer boiler shell allows simpler perpendicular stays to be used between the shells.[1] The Belpaire outer firebox is, nevertheless, more complicated and expensive to manufacture than a round-top version.
Due to the increased expense involved in manufacturing this boiler shell, just two major US railroads adopted the Belpaire firebox, the Pennsylvania and the Great Northern.[2] In Britain most locomotives employed the design after the 1920s, except notably those of the LNER.
Description
In steam boilers, the firebox is encased in a water jacket on five sides, (front, back, left, right and top) to ensure maximum heat transfer to the water. Stays are used to support the surfaces against the high pressure between the outside wall and the interior firebox wall, and partially to conduct heat into the boiler interior.[3]
In many boiler designs, the top of the boiler is cylindrical above the firebox, matching the contour of the rest of the boiler and naturally resisting boiler pressure more easily. In the Belpaire design, the outer upper boiler wall sheets are roughly parallel with the flat upper firebox sheets giving it a squarer shape. The advantage was a greater surface area for evaporation, and less susceptibility to priming (foaming), involving water getting into the cylinders, compared with the narrowing upper space of a classic cylindrical boiler. This allowed G.J. Churchward, the chief mechanical engineer of the Great Western Railway, to dispense with a steam dome to collect steam. Churchward also improved the Belpaire design, maximising the flow of water in a given size of boiler by tapering the firebox and boiler barrel outwards to the area of highest steam production at the front of the firebox.
The shape of the Belpaire firebox also allows easier placement of the boiler stays, because they are at right angles to the sheets.
Despite these claimed advantages, other locomotive boilers such as the
In the USA, the Belpaire firebox was introduced in about 1882 or 83 by R. P. C. Sanderson, who at the time was working for the
Having obtained knowledge of a special form of locomotive boiler (the Belpaire), Sanderson wrote to an old acquaintance from his college days who was working at the
Gallery
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A Victorian Railways J class Belpaire firebox and boiler, in storage. A second firebox can be seen behind.
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British GWR Castle Class locomotive Earl Bathurst. The Belpaire firebox is the square shape in front of the cab.
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AmericanUnion Pacificsteam locomotive #1500, showing the square Belpaire firebox.
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Belpaire firebox and boiler illustrated in Scientific American in 1897.
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A round top boiler and firebox shown for comparison.
See also
References
- ^ Saunders, Lawrence; Blundstone, S. R. (April 1924). "The Belpaire Firebox". The Railway Engineer. 45: 237. Retrieved 2014-08-22.
- ISBN 978-0-253-02799-3.
- ISBN 9785874485672. Retrieved 2014-08-22.
- ^ HAPS AND MISHAPS: The Autobiography of R. P. C. Sanderson, 1940, Philadelphia
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