BELPAIRE

The Standard Firebox of the PRR

(Based on the original article by Richard D. Adams)

The Belpaire firebox (invented by Alfred Jules Belpaire and introduced in 1860) was introduced to the PRR in 1885 when the new Class R, a heavy freight locomotive, rolled out of Juniata in October. Questions remain as to where the design originated and why the Belpaire was placed in this locomotive. Short of correspondence being discovered from Theodore N. Ely, Superintendent of Motive Power, or John B. Collin, Mechanical Engineer, we may never know. However, it would be a reasonable suggestion to say the firebox had its origin in this country at the Bordentown Shops of the Camden & South Amboy Railroad.

In 1847, Robert L. Stevens had Isaac Dripps design a Crampton type passenger locomotive for the C&A. The idea was to have a steady running machine with the drive wheels at the very rear behind the firebox. After all testing was completed, a C&A engine emerged with a sloping firebox using longitudinal crown bars and stay bolts. Other designs using sloping fireboxes followed on other roads using only stay bolts to support the crown sheet.

Why the sloping firebox? In part, it was the result of research in finding a firebox to use coal as locomotive fuel. The secret of burning coal is a large grate surface area and careful firing.

The first locomotive built after Ely's appointment to Superintendent of Motive Power was the Collin design for the Class I (H1). First rolled out in 1875, its unique (for the time) characteristics included: 1) being the first Consolidation produced in quantity as a standard freight locomotive and 2) had an unusual boiler and firebox in that the boiler was made from steel and the top front of the firebox was 9 1/2" lower than the top of the boiler barrel and the sloped steeply to the rear. The space between the roof sheet and the crown sheet, which were flat and had the same slope, was filled with water. This type of construction became so closely identified with the PRR that is was officially known as the "Altoona Boiler". Its mechanical appeal was that it had the roof and crown sheets on the same plane, which meant they could be tied together effectively with stay bolts.

Although experts claimed the sloping firebox had superior steaming qualities, there was a problem of fluctuating water levels in the sight glass while the engine was being worked. The reduction in water space made it difficult to carry water at the proper level. Generally, engineers carried their water higher than necessary. Despite problems, the boiler and sloping firebox remained on PRR freight locomotives until 1885. (The two other classes built with "Altoona Boilers" were Class L, a double-ended passenger locomotive, and M (B3) shifters.)

In 1870, Isaac Dripps, formerly of the C&A, came to the PRR as Master of Machinery. It was after Dripps' tenure that Collin designed a sloping firebox Class I. When it came time to replace the Class I, Collin raised the firebox above the frames and eliminated the nagging problem of a lack of steam space. The Belpaire firebox on the first Class R locomotive, No. 400, was not a radical departure from conventional design; it was a natural extension of the "Altoona Boiler".