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A pumpjack (also called oil horse, donkey pumper, nodding donkey, pumping unit, horsehead pump, rocking horse, beam pump, dinosaur, gasshopper pump, Big Texan, thirsty bird, or jack pump) is the overground drive for a reciprocating piston pump in an oil well. It is used to mechanically lift liquid out of the well if not enough bottom hole pressure exists for the liquid to flow all the way to the surface. The arrangement is commonly used for onshore wells producing little oil. Pumpjacks are common in oil-rich areas. Depending on the size of the pump, it generally produces 5 to 40 litres of liquid at each stroke. Often this is an emulsion of crude oil and water. Pump size is also determined by the depth and weight of the oil to remove, with deeper extraction requiring more power to move the increased weight of the discharge column (discharge head). A pumpjack converts the rotary mechanism of the motor to a vertical reciprocating motion to drive the pump shaft, and is exhibited in the characteristic nodding motion. The engineering term for this type of mechanism is a walking beam. It was often employed in stationary and marine steam engine designs in the 18th and 19th centuries. ==Above ground== In the early days, pumpjacks were actuated by rod lines running horizontally above the ground to an eccentric wheel in a mechanism known as a central power.〔(【引用サイトリンク】title=Oil History: The Central Power )〕 The central power, which might operate a dozen or more pumpjacks, was powered by a steam or internal combustion engine or by an electric motor. Among the difficulties with this scheme was maintaining system balance as individual well loads changed. Modern pumpjacks are powered by a prime mover. This is commonly an electric motor, but internal combustion engines are used in isolated locations without access to electricity. Common off-grid pumpjack engines run on casing gas produced from the well, but pumpjacks have been run on many types of fuel, such as propane and diesel fuel. In harsh climates, such motors and engines may be housed in a shack for protection from the elements. The prime mover of the pumpjack runs a set of pulleys to the transmission which drives a pair of cranks, generally with counterweights on them to assist the motor in lifting the heavy string of rods. The cranks raise and lower one end of an I-beam which is free to move on an A-frame. On the other end of the beam is a curved metal box called a horse head or donkey head, so named due to its appearance. A cable made of steel—occasionally, fiberglass—called a bridle, connects the horse head to the polished rod, a piston that passes through the stuffing box. The polished rod has a close fit to the stuffing box, letting it move in and out of the tubing without fluid escaping. (The tubing is a pipe that runs to the bottom of the well through which the liquid is produced.) The bridle follows the curve of the horse head as it lowers and raises to create a nearly vertical stroke. The polished rod is connected to a long string of rods called sucker rods, which run through the tubing to the down-hole pump, usually positioned near the bottom of the well. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「pumpjack」の詳細全文を読む スポンサード リンク
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