A
1:6 scale model of the Diamond Rope Works Engine, built in 1914 by
Scott and Hodgson, in the
Bolton Steam Museum.
The
prototype is a twin-cylinder compound steam engine of unusual design, being
vertically-arranged like a marine
engine. This saved a lot of floor
space. Power takeoff was from the grooved rim of the 10' diameter
flywheel, which could power machinery on several floors simultaneously via
looped ropes and pulleys.
The Corliss valve gear on the high-pressure cylinder and its linkages are one of the most complex-ever designs, and the most interesting part of the model. The linkages are actuated by a pair of eccentrics on the end of the main crankshaft. The two eccentrics have unequal throw lengths and are offset by 90º relative to one another. Both eccentrics, acting together, actuate the input valves. The outer eccentric, independently, actuates the exhaust valves. The geometry of the link arms which control the shut-off point of the input valves is altered, dynamically, by another set of linkages connected to the centrifugal governor.
On the model, like the prototype, the centrifugal governor is driven from the main crankshaft via sprocket chain and wheels in an enclosed casing. The low-pressure cylinder has a simple slide valve, actuated by a massive eccentric on the main crankshaft between the bedplate and the flywheel.
A large, reciprocating vacuum pump is driven by a pair of rocking arms linked to the low-pressure cylinder crosshead. A much smaller auxiliary pump, mounted on the back of the vacuum pump, is driven from the same rocking arms.
The model used 5/16" large axle and fittings for the main crankshaft. It is back-driven from the flywheel, itself driven by a sprung, rubber tyre held in contact with its rim. The driving wheel and tyre, with a small electric motor, are concealed inside the base.
The engine itself is built mostly in red and green parts, and yellow plates represent the concrete floor and walls of the museum. For clarity, some steam duct pipe work and the access platform and ladders have been omitted from the model. For transport, the model divides into three main sections.
To see the model in action, click a picture on the right.