Grasshopper beam engine

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Animation for Grasshopper Linkage.

Dimensions:
Cyan Link = a
Yellow Link = 2a
Green Link = b
Vertical Distance between Ground Joints ≈ 2a
Horizontal Distance between Ground Joints ≈ b
German stationary engine of 1847

Grasshopper beam engines are beam engines that are pivoted at one end, rather than in the centre.

Usually the connecting rod to the crankshaft is placed between the piston and the beam's pivot.[1] That is, they use a second-class lever, rather than the usual first-class lever.

Origins

William Murdoch's model steam carriage of 1784

The first recorded example of a grasshopper beam was

dredger.[2]

Almost all grasshopper engines placed the crankshaft between the piston and the beam's pivot. This allows a long stroke for the piston, with a shorter stroke for the crank, although with greater force. This was advantageous for early low-pressure steam engines[note 2] that had limited cylinder force but could increase their power by using a longer cylinder. A few exceptions, those of the Americans Oliver Evans' boats and Phineas Davis' Grasshopper locomotives, reversed this and placed the cylinder in between the pivot and crank: a third-class lever.

Many grasshopper engines were built as stationary engines. A few notable early steam locomotives used beam engines, all of which were of the grasshopper pattern. Rather more grasshopper engines were built as marine engines.

Marine engines

Marine grasshopper engine

One of the most important uses for the grasshopper engine was as a marine engine for

centre of gravity for stability and a high crankshaft, suitable for driving paddlewheels. Comet's engine's designer, Henry Bell, had established a pattern for an engine that would be widely used for paddle steamers over the next half-century.[3]

Stationary engines

Unlike the heavy masonry

powering large mills
.

Surviving stationary engines

Video of a grasshopper engine in action at the Museum of Science and Industry in Manchester

Grasshopper steam locomotives

Puffing Billy
Baltimore & Ohio grasshopper Atlantic

Notes

  1. ^ A concept similar to Trevithick's high-pressure locomotive of the same period.
  2. atmospheric engines, these low pressures would soon be superseded following the development of the cylindrical flued boiler
    .
  3. ^ The marine analogue of the beam engine being termed the 'lever engine'
  4. ^ As the crankpin moves in an arc relative to the beam pivot, their horizontal spacing inevitably changes. In the Watt engine, the parallelt link motion allows for this, permitting the cylinder and beam pivot to remain in place. In the grasshopper, the swinging link allows the beam to move slightly about a cylinder and crankpin that remain in the same vertical plane.

References

Wikimedia Commons has media related to Grasshopper beam engines.
  1. ISBN 0-906831-02-4
    .
  2. ^
    ISBN 978-0-19-860782-3
    .
  3. ^
    ISBN 0-946771-55-3
    .
  4. ^ Crowley 1982, pp. 64–65
  5. ^ Crowley 1982, pp. 67
  6. ^ Crowley 1982, pp. 75
  7. ^ Crowley 1982, pp. 95–96
  8. ^ Crowley 1982, pp. 99
  9. ^ Crowley 1982, pp. 102
  10. ^ Crowley 1982, pp. 109
  11. ^ Snell, J.B. (1964). Early Railways. Weidenfeld & Nicolson. p. 38.
  12. ^ Kinert, Reed (1962). "VI: The "Grasshoppers" Have Their Day". Early American Steam Locomotives. Superior Publishing. pp. 53, 56.
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