Boulton and Watt Steam Engine (Powerhouse Museum) - Technical Specifications

Technical Specifications

The engine has a 0.64 metres (25 in) diameter piston with a 1.8 metres (6 ft) long stroke, driven by a mean effective pressure of 70 kilopascals (10 psi). Its top speed is 20 revolutions per minute (rpm) of the flywheel. In the engine's youth, it had a maximum power output of approximately 26 kilowatts (35 hp). It underwent a series of alterations in 1795, converting it from single-acting to double-acting; it was alleged at the time that this conversion improved its power to 52 kilowatts (70 hp), but the Powerhouse Museum claims this is false. A centrifugal governor, which moderates the level of steam produced if the engine begins to overload was added some years after this, and beam and main driving rod, both originally of wood, were replaced in sand-cast iron.

Apart from its age, the engine is notable in that it embodies the four innovations which made Boulton & Watt's engines a significant driver of the Industrial Revolution. The first is a separate condenser, which increases the efficiency of the engine by allowing the main cylinder to remain hot at all times. The second is the parallel motion, which converts the up-and-down motion of the piston into the arcing motion of the beam, whilst maintaining a rigid connection. The rigid connection allowed the engine to be double-acting, meaning the piston could push as well as pull the beam. Third is the centrifugal governor, used to automatically regulate the speed of the engine. Finally the sun and planet gear convert the reciprocating motion of the beam into a rotating motion, which can be used to drive rotating machinery.