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A return connecting rod, return piston rod〕|group=note}} or (in marine parlance) double piston rod engine〔 or back-acting engine is a particular layout for a steam engine. The key attribute of this layout is that the piston rod emerges from the cylinder to the crosshead, but the connecting rod then reverses direction and goes ''backwards'' to the crankshaft. This layout is compact, but has mechanical disadvantages. Return connecting rod engines were thus rarely used. The return connecting rod layout has two possible forms: * The cylinder is between the crosshead and the crankshaft. This requires long connecting rods. To avoid unbalanced forces on the crosshead, these rods are usually paired and run either side of the cylinder. * The crankshaft is between the crosshead and cylinder. This requires a paired piston rod or yoke, so as to pass around the crankshaft. Both horizontal and vertical arrangements have used the return connecting rod layout. Vertical return connecting rod engines used the original 'vertical' layout, with the cylinder facing upwards to the crosshead.〔Although rare today, this was the original layout for all atmospheric and steam engines. The cylinder sat directly atop the boiler below. Even with the development of separate boilers, it was still considered simpler for access to place the large, heavy cylinder low down and with the lighter cranks above. The form of vertical engine that became more common in later years, with the cylinder facing downwards, was originally termed the 'inverted vertical'.〕 == Table and Steeple engines == 'Table' and 'steeple' engines are vertical stationary engines with return connecting rods. === Table engines === Table engines place the cylinder above and between the crankshaft and the crosshead. They saw widespread manufacture by Maudslay from around 1805 and were used to supply power to small engineering workshops. They were especially popular for driving lineshafting, as they could operate at a higher speed than beam engines. Like the smaller grasshopper beam engines, an advantage for Maudslay's table engines was that they could be made in factories as a complete unit. This included their large cast iron baseplate or table. Unlike horizontal engines and house-built beam engines, they did not require the construction of a large and carefully aligned masonry foundation at the engine's site. Engines could also be made in advance and sold 'off the shelf'. Although this had cost savings, it was mostly beneficial because it was ''quicker'' than commissioning the building of an engine and engine house to go with it. === Steeple engines === Steeple engines place the crankshaft above the cylinder, between it and the crosshead. They use paired piston rods, two or even four, from the piston to the crosshead, to avoid the crankshaft. Another pattern used a triangular yoke on the single piston rod, allowing the crankshaft to pass through it. Steeple engines were mostly used as marine engines.〔 Some American paddlewheel riverboats had especially large steeples that towered over their deckhouse. The term 'steeple engine' was also used later to refer to inverted-vertical tandem-compound engines, owing to their great height.〔A tandem compound places both high and low pressure cylinders, sometimes even a third intermediate pressure cylinder, in-line on the same piston rod.〕 These were not return connecting rod engines. 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「return connecting rod engine」の詳細全文を読む スポンサード リンク
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