1262

THEORY AND PRACTICE OF ENGINEERING.

Book II.

The arms k,k, serve as rests to the balls when the engine is not at work, and the rodc is raised to such a height that the throttle-valve is in a horizontal position, and thepassage of the pipe open for the admission of steam: by the pipe DI) the steampasses either to the top or bottom of the cylinder through the throttle-valve a , and thendown to the condenser, through the pipes E, E : the valves n,o, have each a spindle passingthrough the stuffing-boxes r,s. The rods of the valves p and q have also at t and u stuffing-boxes to pass through, which rods open the eduction pipe E; thus the valves for theadmission or eduction of the steam are opened without any escape. The sliding rods,which give motion to these valves, are kept in a perpendicular position by bands.

Modes of opening Valves, Cocks, and Slides , or the means by which the engine is renderedautomatic, or capable of performing its work without the assistance of manual attention toopen and shut them, is a matter of the greatest importance, and lias partly been described;but one of the most perfect is that of deriving the motion of the valves from a connecting

Fig. 2014.

ECCENTRIC STEAM VALVE.

rod, one end of which is made to move round in the circle of a crank, while the other endperforms a rectilineal or circular reciprocating motion : another method is by

The Eccentric, which is a circular disc or ring of metal, placed upon the shaft or axis,turned by a crank. The distance from the centre of the disc to the centre of the axisis called the eccentricity, and is equal to half the throw or range of the motion ofthe valves to be moved by it; the rod is called the eccentric rod, and is attached to ahoop that exactly fits the disc : this produces an easy change of motion, and beingconstantly moving gives no stroke at the time of change. Suppose r to be the radius ofthe eccentric circle, and d the distance of its centre ; from the centre of motion thenr + d — (r — d) will be the extent of the movement, =2 d, or twice the eccentricity.. At £of the stroke, counted from either end, a valve can only be opened half way; at £ part ofthe stroke it may be calculated to be fully open : sometimes the valve rods are madeto branch out into four portions, and at their separation a flat brass plate is inserted, withanother at the summit to unite them : the eccentric works between the side forks of therod, and bears against its top and bottom plates, figs. 2015. 2017. : the other forks arein width equal to the diameter of the axle, which prevents the rod deviating from thevertical position, figs. 2016. 2018.; by adding a handle that can be worked by hand, thereversing process may be performed.

Fig. 2015.

Fig. 2016.

Fig. 2017.

Fig. 2018.

The Governor , or Centrifugal Power Regulator , is an ingenious contrivance for equalisingmotion, in the steam-engine particularly; by its means the valves which suffer thesteam to pass from the boiler to the cylinder are opened or closed to the extent necessary,and in such a manner as to allow a certain quantity of steam to pass through, and no