The
Fusible Plugs.PDF article attached to MD Ramsey's July 30th posting is from the October 1933 issue of The Boiler Maker. I believe that all 3 authors were Southern Pacific master boilermakers / boiler maker general foremen. Certainly Frank A. Longo was. All the data presented is for S.P. locomotives. Note the important differences (explained in the text) between Figure 3 and Figure 4 designs.
Southern Pacific's Mechanical Circulars include a detailed assembly procedure, including quality control test equipment and required % to be tested from each assembly lot. Project 2472 sold photocopies of these Mechanical Circulars back in the late 1970s-1980s. I will look for my copy, scan it into a PDF, and post it within 2 weeks.
S.P.'s fusible plug design addresses the concerns posted about tin (fusible layer) oxidation, partial melting, etc. I have always been surprised that it did not become the railroad industry standard worldwide.
- Doug Debs
SP Fusible Drop Plugs-1.pdf