British Railways Standard Class 9F steam locomotives Nos 92020-9 were experimentally built with Franco-Crosti boilers, thus forming a subclass. All ten were built in 1955 at Crewe Works.
The Franco-Crosti boiler took the form of a single cylindrical water drum running along the underside of the main boiler barrel; the standard chimney at the front was only used during lighting-up, in normal working the gases went through firetubes inside the preheater drum that led to a second smokebox situated beneath the boiler from which there emerged a chimney on the right-hand side (fireman's), just forward of the firebox.
In the event, the experiment did not deliver the hoped-for benefits, and efficiency was not increased sufficiently to justify the cost and complexity. Moreover, conditions were unpleasant on the footplate in a cross-wind, this in spite the later provision of a small deflector plate forward of the chimney. These problems led to the subsequent sealing off of the preheater drum, over the period 1959-1961, and the locomotives were then worked conventionally. As a result of this, there was a reduced ability to generate steam, and so their power classification was reduced from 9F to 8F.
All were fitted with the BR1B-type 4,275 imperial gallons (19,430 l) tender.
No. | Built | Converted to conventional | Withdrawn |
---|---|---|---|
92020 | March 1955 | 1961 | November 1967 |
92021 | March 1955 | 1960 | November 1967 |
92022 | March 1955 | 1962 | November 1967 |
92023 | March 1955 | 1961 | November 1967 |
92024 | June 1955 | 1960 | November 1967 |
92025 | June 1955 | 1960 | November 1967 |
92026 | June 1955 | 1959 | November 1967 |
92027 | July 1955 | 1960 | August 1967 |
92028 | July 1955 | 1959 | October 1966 |
92029 | July 1955 | 1960 | November 1967 |
No. 92028 was the first Franco-Crosti 9F to be withdrawn in October 1966, with 92027 following in August 1967, but the remainder were withdrawn en masse in November 1967. All were scrapped.
Year | No. Withdrawn | Nos |
---|---|---|
1966 | 1 | 92028 |
1967 | 9 | 92020–7/9 |