Lightmoor Beam Engine
NOTE: This entry does NOT relate to the beam engine from Lightmoor Brickworks, Shropshire, which is now at Ironbridge.
This engine was installed at Lightmoor Colliery, Ruspidge, in the Forest of Dean, where it worked until 1940. It is now preserved at the Dean Heritage Centre
It is believed to have been made c.1830 by Samuel Hewlett at the Soudley Foundry, the site of which is now home to the Dean Heritage Centre. Evidence for this, together with interesting information about the engine, was presented in 'The Lightmoor Colliery Winding Engine' by A K Pope, available online .
This engine had a sister at Lightmoor Colliery, and a former employee recalled that when that engine was scrapped in 1934, it had the name Hewlett, Aylesford (Soudley) and a date believed to be 1828 cast into the UNDERSIDE of the bedplate.
Some sources give the engine a date of 1805. Various features of the design make this unlikely, although some aspects, such as the thin bedplate, would not be inconsistent with such an early date. Furthermore, it has not been established whether Hewlett - if indeed he was the maker - had a foundry and other necessary facilities at that date.
'The Lightmoor Colliery Winding Engine' by A K Pope highlights interesting aspects of the engine's design and construction, some of which are described here.
The piston rod is guided by vertical bars. It is thought that these may have superseded an earlier arrangement using Watt's parallel motion, which would have utilised the redundant pin seen on the beam.
A surprising feature is the presence of a wrought iron strap surrounding the periphery of the cast iron beam. Straps were sometimes fitted to engine beams as reinforcement to prevent or arrest cracks. The fitting of straps was usually accompanied by the fitting of a 'bridle' above the beam, and the straps were usually tightened by tapered cotters. Examples can be seen on beam engines at Kew Bridge Steam Museum. However on the Lightmoor engine there is no bridle and there are no cottered joints, and it is by no means clear how the strap was fitted in such a way as to ensure adequate tightness.
The beam's pivot or 'axle' is an octagonal-section wrought iron bar. This is 'staked' into the bosses on either side of the beam. To avoid the risk of the cast iron bosses 'bursting' by the stakes being driven in, the bosses were reinforced by having wrought iron hoops shrunk on.
The engine's four columns are connected to the beam's pivot block, and part of the cast iron block has broken away, and the flange has cracked on the LH rear column. An extra bolt has been fitted here. A 1934 photograph shows that an iron strap was fitted between the two 'rear' columns above the collars.
The flywheel has curved wrought iron spokes cast into a cast iron rim and hub. This construction avoids a risk inherent in making a flywheel as a single casting, namely the possibility of spokes fracturing as the iron cooled in the mould. The use of curved wrought iron spokes with cast iron rim and hub is very unusual in steam engines. The outside of the rim appears to be worn, perhaps due to a brake being applied here in service (its present bright appearance comes from the friction drive now used to demonstrate the engine in motion).
At least three other engines with similar flywheels (having wrought iron spokes with double curves) are known to have survived in the UK. One is an 1855 Davy Bros horizontal engine at Abbeydale Industrial Hamlet. Another is a vertical engine preserved outdoors in Darwen, ex-Sunnybank Mill. The third is a beam engine at the National Railway Museum, Shildon.
As for the flywheel, the cast iron pinion is 'staked' onto square crankshaft. The pinion drove a winding drum via a larger gear
The valve gear was worked by a slip eccentric. With this arrangement the eccentric was able to rotate, within limits, on the crankshaft. This allowed the engine's direction of rotation to be reversed. A counterbalance weight which was bolted to the 'loose' eccentric sheave.
The bedplate ('entablature') is a relatively thin casting, basically a plate. Later engines would have a deeper box section casting for stiffness. The feet of the sloping columns locate in cast-in recesses on the bedplate.
Sources of Information
-  'The Lightmoor Colliery Winding Engine' by A K Pope, reprinted from the Gloucestershire Industrial Archaeology Journal for 1982, pp.7-12
- Plate 77, 'Stationary Steam Engines of Great Britain, Volume 6: The South Midlands', by George Watkins, Landmark Publishing Ltd