Chapter XVII: The Valve-Motion 199

The Locomotive Slide-valve.--Invention and Application
of the Slide-valve.--Description of the Slide-valve.--
Primitive Slide-valve.--Outside Lap.--Some Effects of
Lap.--Inside Lap.--The Extent of Lap usually adopted.--
First Application of Lap.--The Allen Valve.--Advantages
of the Allen Valve.--Case where the Allen Valve proved
its Value.--Inside Clearance.--Lead.--Operation of
the Steam in the Cylinders.--Back Pressure in the
Cylinders.--Effect of too Much Inside Lap.--Running into
a Hill.--Compression.--Definition of an Eccentric.--
Early Application of the Eccentric.--Relative Motion of
Piston and Crank, Slide-valve, and Eccentrics.--Attempts
to Abolish the Crank.--Valve Movement.--Effect of
Lap on the Eccentric’s Position.--Angular Advance of
Eccentrics.--Angularity of Connecting-rod.--Effect on
the Valve-motion of Connecting-rod Angularity.--Aids
to the Study of Valve-motion.--Events of the Piston
Stroke.--What Happens Inside the Cylinders when an Engine
is Reversed.--Events of the Stroke in Reversed Motion.--
Purpose of Relief-valve on Dry Pipe.--Using Reverse-motion
as a Brake.

CHAPTER XVIII.

THE SHIFTING-LINK 229

Early Reversing Motions.--Invention of the Link.--
Construction of the Shifting Link.--Action of the Link.--
Valve-motion of a Fast Passenger Locomotive.--Effect of
changing Valve-travel.--Weak Points of the Link-motion.--
Why Decreasing the Valve-travel Increases the Period of
Expansion.--Influence of Eccentric Throw on the Valve.--
Harmony of Working-parts.--Adjustment of Link.--Slip of
the Link.--Radius of Link.--Increase of Lead.

CHAPTER XIX.

SETTING THE VALVES 246

The Men who learn Valve-setting.--Best way to learn
Valve-setting.--Preliminary Operations.--Connecting
Eccentric-rods to Link.--Marking the Valve-stem.--Length
of the Valve-rod.--Accuracy Essential in Locating the Dead
Center Points.--Finding the Dead Centers.--Turning Wheels
and Moving Eccentrics.--Setting by the Lead Opening.--
Ascertaining the Point of Cut-off.--Adjustment of Cut-off.

CHAPTER XX.

LAYING OUT LINK-MOTION 257

Preliminary Explanations.--Definition of Terms used.--
Conditions.--Problems Involved in Laying Out
Link-motion.--To find the Position of Crank when the
Piston is at Full and Half Stroke.--To find the
Center Line of Motion and the Amount of Offset in the
Lower Rocker-arm.--To find the Relative Positions of
Crank-pin and Eccentrics when the Piston is at Full and
Half Stroke.--To determine the Correct Length of the
Eccentric-rods.--To find the Position of the Center
of Saddle-pin.--To Find the Position of the Center of
Lifting-shaft and the Length of its Arms.--Dimensions of
Locomotives.

CHAPTER XXI.

THE STEVENS VALVE-GEAR 287

Description of Motion.--Arrangement of the Motion.--Valve
Movement.--Valve-stems and Stuffing-boxes.--How Movement
of Valve is Governed.--How Exhaust Lead is Controlled.

CHAPTER XXII.

THE JOY VALVE-GEAR 292

Description of Motion.--How to Apply this Gear to American
Locomotives.--Construction Directions.--How Lap and Lead
are Regulated.--Advantages claimed for the Motion.--
Action of the Motion.--Rules for laying down the Center
Lines of the Motion.

CHAPTER XXIII.

THE STEAM ENGINE INDICATOR 303

Purpose of the Indicator.--Description of Instrument.--
Operation of the Indicator.--Lines of the Diagram.--
Data Necessary for Analyzing the Diagram.--Advantages of
Indicating Locomotives.