This crane tank locomotive was built by Robert Stephenson & Hawthorn in 1942.
Two locomotives (Works Nos 7006 & 7007) had been supplied by Robert Stephenson & Hawthorn to William Doxford and Sons in 1940 which were to a Hawthorn Leslie design dating from 1918. In 1942 another two were supplied (Works Nos 7069 & 7070)
The locomotives could lift weights up to 4 tons. They had 12 x 15 outside cylinders and 2 ft 10 in diameter driving wheels. These engines are unusual as they had outside Joy’s valve gear.
The design of the crane is interesting in that the elevation of the jib is done using the pressure within the boiler, only the slewing being done by a separate steam engine. The jib could also be depressed downwards. Because of this, the hooks on the jib were fixed, being positioned for lifting various weights up to four tons according to their distance along the jib. This obviated the need for a winch and drum or separate engine for operating this. The jib was raised and lowered using a piston at its rear, working within a cylinder atop the boiler (itself notable for the vertical circular firebox which also forms the base of the crane). Steam pressure from the boiler was constantly fed to the top of the piston, the lifting/lowering being achieved by admitting steam to the underside. If steam was admitted, then the piston would be in equilibrium and the weight of the jib would cause it to lower. By exhausting steam from the underside of the piston, the boiler pressure would act upon the top and so cause the jib to be raised – this enables any position to be positively locked and a very precise control to be exercised over the lift. With the engine out of steam the jib would be inclined to settle downwards, so the chimney provides support for the jib at the front end.
7070 was one of nine locomotives that worked at the Pallion Shipyard of William Doxford & Sons Ltd. in Sunderland yards moving materials from the reception areas to the slipways where ships were constructed.
The Pallion Shipyard of William Doxford & Sons Ltd was founded in 1840 by William Doxford. It was acquired by Northumberland Shipbuilding Company in 1918. It was renamed Doxford & Sunderland Shipbuilding & Engineering Co Ltd in 1961 and Doxford & Sunderland Ltd in 1966. In the 1970s a new all-weather Pallion yard was built which could build two ships of up to 30,000 tons deadweight side-by-side. The steel came in at one end, and the completed ship left from the other with engines installed and sometimes with the machinery running.
The remaining tank engines were retired in 1971 with all four of the Robert Stephenson & Hawthorn locomotives surviving into preservation.
- 7006 Roker at the Tanfield Railway but now on loan to Beamish Museum
- 7007 Hendon at the Tanfield Railway
- 7069 Southwick at the Keighley & Worth Valley Railway
- 7070 Millfield at Bressingham Steam Museum
7070 Millfield is currently stored out of use at Bressingham Steam Museum