HOW THE STEAM­ROLLER WORKS

Landscape (UK) - - History And Heritage -

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.

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