NICHOLAS DE SCIOSE / SCIENCE PHOTO LIBRARY NICHOLAS DE SCIOSE / SCIENCE PHOTO LIBRARY
An oil worker tending to a jack pump. These pumps (also known as 'nodding donkeys') are used where the natural pressure in the oil well is too low to force oil out at an economic rate. The pump uses a series of non-return valves to draw the oil out as the 'head' nods up and down. Such pumps are now becoming less frequently used as new recovery techniques are developed.
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