673  4-2-2  Midland Railway  MR Class 115

673

 

Power Classification
Introduced 1896 – 1899
Designer Johnson
Company Midland Railway
Weight – Loco t cwt
               Tender t cwt
Driving Wheels 7ft 9½ins
Boiler Pressure 170psi
Cylinders Inside – 19in x 26in
Tractive Effort 15,279lbf
Valve Gear

Introducing an engine design that had a single driving wheel in 1887 may appear to be a strange decision as it was twenty-one years since the last such locomotive had been built. The logic would appear to have been based on the Midland Railway (MR) policy of small engines, the lack of gradients on the lines south of Derby and the invention of a steam-powered sanding device. The sanding device was invented by Francis Holt who was the Works Manager at Derby and it greatly improved the adhesion of larger diameter wheels on wet and slippery rails.

The theory behind a large single driving wheeled locomotive was that the bigger the wheel the faster it could go. Because of the reduced number of revolutions of the driving wheel the fewer were the interactions between the valve gear, piston and cylinders which was highly desirable whilst the science of lubrication was still in its infancy.

Johnson produced a number of designs for 4-2-2 locomotives with the first being built at Derby in 1887. This had 7ft 4in diameter wheels. It was not until 1896 that Johnson introduced the class 115 engines which had 7ft 9½ins diameter wheels and larger cylinders than earlier designs. A total of 15 engines of the 115 class were built between 1896 and 1899 by which time the MR had built 115 single wheeled locomotives.

It was quite common for the 115 class engine to pull a typical Midland express weighing 200 and 250 tons which suited the Class 115 perfectly. Given a dry rail they could maintain a tight schedule with 350 tons. Speeds up to 90 mph were not uncommon and the sight of their whirring huge driving wheels earned them the nickname “Spinners”. Because of the Midland’s practice of building low powered locomotives and relying on double-heading to cope with heavier trains many enjoyed working lives of up to 30 years. They made ideal pilot engines for the later Johnson/Deeley 4-4-0 classes.

Preservation

673 (MR 118, MR 673 and LMS 673)

673.jpg

118 was completed at Derby works in 1897. It became 673 in 1907, and LMS 673 in 1923. It was withdrawn from service in 1928 and repainted in MR colours with its original number, but no longer in working order.

It is the oldest preserved engine in Britain to have been built new with piston valves.

The replica chimney is of the original design but is in fact a wooden dummy.

It was kept in derby works for many years and periodically brought out on special occasions.

It was steamed around 1976–1980 when it took part in the Rainhill Trials 150th cavalcade but is currently a static exhibit in the National Railway Museum in York as part of the National Collection.

 

Home Base Current Status Owner
National Railway Museum – York Static display National Railway Museum NRM Object Number{1978-7023}
673 at York.jpg 673 in the National Railway Museum at York-2009

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