English: A Network Rail train of YKA-B 'Salmon' 50 ton bogie sleeper carrier wagons at Keynsham, Somerset, 21 February 2021.
894 unfitted or piped 'Salmons' (some were later fitted with vacuum brakes) were built in 1949-62, based on a LMS design (with 5 bolsters), in several varieties: 54 unfitted Diag.1/640 with planked flat floor (no bolsters) built by BR (Derby) and Teeside B&E in1949-52; 147 unfitted Diag.1/642 (first lot with bolsters but second without) built by Head-Wrightson (Thornaby) in 1951-53; 54 unfitted Diag.1/644, steel floor, non-bolstered, built by G R Turner in 1954; 315 unfitted Diag.1/646 with steel floor (as Diag.1/644) built by G R Turner and Teeside B&E in 1955-57; 191 Diag.1/637 (piped version of Diag.1/646) built by BR (Wolverton) and Head-Wrightson in 1959-61; 25 piped Diag.1/628 (as Diag.1/637 but with side guide rails) built by Powell Duffryn in 1961-62. Many post-1952 wagons were fitted with air brakes in the 1980's and then rebogied in 1999-2008 for higher speeds, being coded YWA under TOPS for use as sleeper carriers. Others were modernised by Marcroft in 2009 for use as rail track panel carriers and coded YKA.
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