Return connecting rod engine

A return connecting rod,return piston rod 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:

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.

'Table' and 'steeple' engines are vertical stationary engines with return connecting rods.

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 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.

...
Wikipedia