| March/April 1977

  • Instantaneous effective crank
    FIGURE 1
  • Instantaneous effective crank
    FIGURE 2

  • Instantaneous effective crank
  • Instantaneous effective crank

1961 West Side Drive, Rochester, New York 14624.

The term 'instantaneous effective crank' is a common one in engineering, but I find that relatively few steam engine operators are aware of it.

I have read article after article trying to show that the torque on the 'out' stroke was greater than on the 'in' stroke and that the difference is larger than accounted for by the neutralization of a part of the piston area by the presence of the piston rod itself. The statements were true, but the explanation left something to be desired.

The torque is greater on the 'out' stroke because the instantaneous effective crank is longer during that part of a revolution utilizing full steam chest pressure on the piston; i.e. - not during the expansion and exhaust part of the stroke.

The effective length of the crank charger continually throughout a revolution and when the valve passes through zero as it does twice per revolution, the engine has no torque at all and is said to be on 'dead center'.

The two figures will illustrate the term 'instantaneous effective crank' and how it varies throughout the cycle. In both Figures 1 and 2, the angles of divergence of the connecting rods (center lines are D-E) from the crankshaft-crosshead (center liner B-C) are constructed equally. With the connecting rods being 'free pinned' at both ends, they can exert only a push or a pull and that only along the paths of their centerlines.


Farm Collector April 16Farm Collector is a monthly magazine focusing on antique tractors and all kinds of antique farm equipment. If it's old and from the farm, we're interested in it!

Save Even More Money with our SQUARE-DEAL Plan!

Pay now with a credit card and take advantage of our SQUARE-DEAL automatic renewal savings plan. You'll get 12 issues of Farm Collector for only $24.95 (USA only).

Or, Bill Me Later and send me one year of Farm Collector for just $29.95.

Facebook Pinterest YouTube