How to construct a Reuleaux Diagram

1)Draw a circlewith the diameter equal to the valve travel under consideration. In this illustration we draw the diagram, when the valve travel is 275mm.

2) Now draw two lines parallel to the vertical axis, one offset by the steam lap, and the other by the lead - in this case 65mm and 7mm respectively:

3) Draw a diameter from the point where the Lead line intersects the circle, and another diameter at right-angles to it.

4) Draw two lines parellel to the last-drawn diameter, the first offset on one side by the steam lap (65mm) and the second offset to the other side by the exhaust lap (18mm).

5) It will be discovered that the distance between the upper (steam lap) line and the nearest axis of the circle exactly equals the lead (7mm). Draw Admission, Cut-off, Release and Compression lines as shown below.

6) Draw verticals from the points where the Admission, Cut-off, Release and Compression lines meet the circle. The distances from the edge of the circle represent the point where each valve event occurs. These distances can be converted to percentages - see below.

From the diagram above: Cut-offoccurs at a distance of 206.69mm from the left of circle. 206.69 275 = 0.7516 = 75% (i.e. maximum cut-off); Releaseoccurs at 263.06 mm or 263.06 275 = 0.9566 = 96% Compressionoccurs at 30.79 mm = 30.79 275 = 0.1119 = 12% Admissionoccurs at 0.24 mm = 0.24 275 = 0.0009 = 0.1%