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"Since the valve must move a distance equal to the outside lap before admission can take place, it is evident that the eccentric can no longer be at right angles to the crank at the beginning of the stroke, but must be ahead of the right—angle point by an amount equal to AOC." —Derr, 1911

Valve with Lap of Steam Engine at Extreme Left with Exhaust Ports Open

"Since the valve must move a distance equal to the outside lap before admission can take place, it is…

"The maximum displacement of the valve is attained when the eccentric is horizontal. In this position both the steam and exhaust ports are wide open, and any further motion motion of the piston will cause the valve to move toward its mid position." —Derr, 1911

Valve with Lap of Steam Engine Where Steam Enters the Slide Valve Compartment

"The maximum displacement of the valve is attained when the eccentric is horizontal. In this position…