The remedy in this case is to set the eccentric back.
With less compression the point a would be lower.
Fig. 3377.
Excessive lead is shown in [Fig. 3377] by the loop at a, where the compression curve extends up to the steam line, and the lead carries the admission line above it, because of the piston moving against the incoming steam.
To mark in the theoretical compression curve, the vacuum line and the clearance line must be drawn in as in the figure, and ordinates must be drawn.
According to the diagram, in [Fig. 3377], the compression is clearly defined to have begun at c, and at that time the space filled by steam is represented by the distance from c to the clearance line. The pressure above vacuum (or total pressure) of the steam in the cylinder when the compression began is represented by the length or height of the dotted line 1.
Now suppose the piston to have moved from the point c, where compression began, to line 2 (which is midway between line 1 and the clearance line), and as the compressed steam occupies one-half the space it did when the piston was at c, therefore the steam pressure will be doubled, and line 2 may be drawn making it twice as high as line 1.
Line 2 is now the starting point for getting the next ordinate, and line 3, must be marked midway between line 2 and the clearance line, and twice as high as line 2, because at line 3 the steam will occupy half the space it did at line 2. Line 4 is obviously midway between line 3 and the clearance line.