A feed with a composition
is flashed (vaporized). On the
diagram, the slope of the purple line is
are the numbers of moles of liquid and vapor leaving, respectively. The intersection of the
line with the black equilibrium curve gives the mole fractions of methanol in the exiting vapor (green) and liquid (blue) streams. Because VLE is assumed, the mole fractions of methanol in these streams correspond to the horizontal line on the
diagram. The purple dot on the
diagram represents the feed mole fraction of methanol, and the lever rule is used to determine the liquid/vapor molar ratio.
 P. C. Wankat, Separation Process Engineering: Includes Mass Transfer Analysis
, 3rd ed., Upper Saddle River, NJ: Prentice Hall, 2012.