HOW THE STEAMROLLER WORKS

A steamroller works in a similar way to a railway locomotive. At the back of the engine is the footplate for the crew and the firebox with its coal fire. In front of that is the barrel. This is the boiler, containing 28 tubes, 2in (5cm) in diameter. These run from the firebox down to the smoke box below the chimney at the far end of the vehicle. The hot gases from the fire pass down the tubes to heat the water in the boiler. They act in the same way as the elements heat an electric kettle. The pressure inside the boiler steadily builds up. Eventually, it reaches a level where it has enough power to make the engine work. For the Hurleys’ steamroller, the normal working pressure is 130lbs per square inch. In comparison, a 10st (63.5kg) woman standing on both feet exerts approximately one tenth of that pressure on the ground. Once working pressure is reached, the steam is released to push the piston inside the single cylinder on the engine. Valves ensure that steam alternates between one side of the piston and the other, driving it backwards and forwards. The piston connects to a crank that turns the wheels to drive the engine. The driver of the steamroller shovels the coal and manages all the controls. There are two main ones, the regulator and the reversing lever. The regulator governs the amount of steam passing from the boiler to the engine. As well as being either fully forward or back, the reversing lever can be placed in intermediate positions. This adjusts the time during the piston stroke that steam is admitted into the cylinder before being cut off. It makes for more economic running. The driver is in charge and must have an appropriate G driving licence for road rollers. David is the driver in the family, although Jo plans to apply for a licence eventually. She does drive, but at the moment can only do so on the road accompanied by David. Jo can, however, steer the 19ft-long roller, a separate job to driving it, and no easy task. The massive iron front roller is connected to chains wrapped round a cylinder. This in turn is connected to the steering wheel. The engine has a tendency to wander to one side of the road or the other, depending on the camber. Jo has to constantly adjust the steering. Each time she wants the steamroller to change direction, she has to take in the slack on the chain at that side. She does this by turning the steering wheel four or five times. To make a full turn takes 40 turns. While the engine is running, Jo is constantly turning the wheel, first one way, then the other. There is a real skill to this. “You don’t get an instant response from the roller because you have to take up the slack on the chain,” she explains. Getting that just right takes a lot of practice.