Ruston-Proctor's Expansion Gear.-Fig. 42 illustrates the automatic expansion gear made by Messrs. Ruston, Proctor & Co., Lincoln. The governor is of the Porter type; and is actuated from the crank shaft by means of bevel gear. The radius link is pivoted on the bottom end, and the lifting link from the governor raises or lowers the radius rod as circumstances require. A dashpot is fitted to give steadiness to the governor, and the balance weight relieves the latter from all encumbrance due to the radius rod.

Crank-Shaft Governor Expansion Gear.-It has been remarked that the grade of expansion can be varied by altering the angular advance of the expansion eccentric. Fig. 43 is a diagram Fig 43.

for this class of gears. OA is the position and throw of the main or distribution eccentric; and OB the expansion eccentric. CD is the lap circle, which, in this instance, is negative. Cut-off is at OE. Suppose B moved round the shaft to position O B', then OF is the cut-off line.

Fig. 44 illustrates a device whereby the angle of O B can be varied according to circumstances. The figure is self-explanatory, and it is only necessary to remark that the design admits of considerable adjustment. In the first place, the point of attachment of the springs to the levers carrying the weights B B can be altered; the position of the weights themselves can be adjusted by

means of the nuts on the levers; and the connecting links A A are also adjustable.

The third method of obtaining a range of expansion is by varying both the throw and position of a simple slide valve eccentric. The principle of this class of gears is set forth in the accompanying diagram.

Let OA (Fig. 45), represent the throw and position of the eccentric relative to the true position of the crank O B. CD is the outside lap circle, and cut-off is at OE. Let the eccentric be altered so that its throw and position are given by the line OA. The lap circle will remain the same, and the cut-off will therefore be at O F. Westinghouse Governor.-As a typical example of this class of gears, the Westinghouse governor and eccentric is selected. Fig 46.

Assumed Crank Postion

Real Crank Position

Westinghouse Governor (position for latest cut-off).

Fig. 46 shows the position of the parts for the latest cut-off, which is at O A. In Fig. 47 the gear is in position for earliest cut-off, which is at O A. The real and assumed crank positions are indicated on each figure, as is also the direction of rotation. The valve diagrams show that as the governor moves from latest to earliest cut-off, the lead increases. This governor operates upon a piston valve, which is the most suitable form for crank-shaft governors, as the work required to move the valve passes partly through the springs.

Crankshaft governors find much favour in America. The

Dick and Church governor, as made by the Phoenix Iron Works Company, is representative of its class.

Fig 47.

Assumed Crack Posit

Real Crank Position

O

Westinghouse Governor (position for earliest cut-off).

The principal forms of slide valve expansion gears have now been dealt with. The varieties and modifications are numerous, but the action is generally little different from the gears that have been described, a knowledge of which will enable the action of other gears to be understood.

CHAPTER III.

LINK MOTIONS.

CONTENTS.-Single Eccentric Reversing Gear-Valve Diagram for shifting Eccentric Gear-Stephenson's Link Motion-Open and Crossed RodsValve Diagram for Stephenson's Link Motion-Mr. Macfarlane Gray's method of describing the Characteristic Line - Crank Pin DiagramBest arrangement of Gear-Link Motion made by the North - Eastern Railway Company-The Slot Link - The Double bar Link with Eccentric Rods inside The same with Eccentric Rods outside-Proportions of Links-Gooch's Link Motion - Eccentrics driving obliquely — Valve Diagram for Gooch's Link Motion - Crank Pin Diagram --Best arrangement of Gear-Allan's Sraight Link Motion-Diagram for Allan's Gear -Expansion Gears and Link Motions combined.

To enable an engine to run in either a forward or backward direction, it must be fitted with link motion, or some other equivalent device; and it remains to discuss various gears by means of which reversal is effected.

Single Eccentric Reversing Gear. The simplest form of reversing gear consists of an eccentric, the angle and throw of which can be varied at will by moving it across the shaft. This device, although simple and efficient, would be very inconvenient, especially on an engine of large size, or on one that required frequent reversal; and the arrangement is here described, not because of its practical utility, but because of the principle involved—the principle of link reversing gears.

The single eccentric reversing gear consists of a plate A, secured to the crank shaft B by means of a key. The eccentric C is provided with two slots, whereof the larger is to allow of the eccentric being moved on the shaft, so as to take either the position shown by the upper or lower diagram, Fig. 48, or any intermediate position between the extreme limits. The second slot is made to pass the bolts DD, which are securely fixed in the plate A. This arrangement permits of the eccentric being held in any position between E and F.

In the diagram the position of crank is indicated, and also the centre line of the eccentric. It will be understood that when the eccentric is secured so that it coincides with the line K E-its extreme position in one direction-the engine will run in the direction of the arrow, and when the eccentric has the position K F, the motion is reversed The reason of this is clear. Consider first the upper diagram, where the crank is on dead centre, and the line KE is the position of the eccentric. The cylinder is supposed to lie to the left of the figure. Motion by piston effort