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 <a href="/facts/Steam_engine/f7hN8vzm">steam engine</a>.
The key attribute of this layout is that the <a href="/facts/Piston_rod/yDX8UhRb">piston rod</a> emerges from the cylinder to the <a href="/facts/Crosshead/nhEhrxYo">crosshead</a>, but the <a href="/facts/Connecting_rod/AXp1gPdh">connecting rod</a> then reverses direction and goes backwards to the <a href="/facts/Crankshaft/oYCe9nB3">crankshaft</a>. This layout is compact, but has mechanical disadvantages. Return connecting rod engines were thus rarely used, except in some mid-19th century marine applications where they had certain advantages.
The return connecting rod layout has two possible forms: 

<ul><li>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.</li>
<li>The crankshaft is between the crosshead and cylinder. This requires a paired piston rod or yoke, so as to pass around the crankshaft.</li></ul>
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.

Return connecting rod engine open-in-new

Return connecting rod engine