Steam Engine Specifications/Work Diagram Construction

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Main > Energy > Steam Engine

Construction of a Work Diagram

Steam Engines-fig-7.png

Refer to fig. 7 in "Steam Engines'


  1. Determine the initial pressure, ratio of expansion, and percent of clearance.
  2. Draw lines OX and OY at right angles.
  3. Make OR the clearance displacement percent.
  4. Make RX the length of the stroke
  5. Draw RA perp. at the clearance displacement length to represent 3-8% (med. speed engine) of the total displacement.
  6. Draw AK at 0.98 of the boiler pressure
  7. Draw KX at the stroke length.
  8. Draw LH at 14.7 psi for atmospheric pressure.
  9. Locate cutoff point B for expansion ratio (1/8, 1/4, etc. of stroke len)
  10. Divide BK into equal distances (a,b,c, etc)..
  11. Connect them to point O
  12. Extend horizontals from the points where diagonals meet with line BP.
  13. Extend verticals down from (a,b,c, etc)
  14. Connect these points to form the expansion curve.
  15. Back pressue curve at FD about 2psi above atmospheric
  16. Compression curve at DE, rounded up to start of cycle.

Area of actual diagram is slightly smaller than the theoretical:

Large, med. speed 0.90
Small, med. speed 0.85
High speed 0.75