Part 2 (1/2)

[Illustration: FIG 15--Diagra the principle of a steam-injector]

[Illustration: FIG 16--The Giffard injector]

A for 16) Stea up the valve V As it rushes through the nozzle of the cone A it takes up water and projects it into the ” cone” B, which can be raised or lowered by the pinion D (worked by the hand-wheel wheel shown) so as to regulate the amount of water admitted to B At the centre of B is an aperture, O, co with the overflow The water passes to the boiler through the valve on the left

It will be noticed that the cone A and the part of B above the orifice O contract doard This is to convert the _pressure_ of the steam into _velocity_ Below O is a cone, the diameter of which increases doards Here the _velocity_ of the water is converted back into _pressure_ in obedience to a well-known hydromechanic law

An injector does not ell if the feed-water be too hot to condense the steam quickly; and it may be taken as a rule that the wariven weight of stea the overflow orifice, to prevent air being sucked in and carried to the boiler

When an injector receives a sudden shock, such as that produced by the passing of a locomotive over points, it is liable to ”fly off”--that is, stop h the overflow If this happens, both steam and water must be turned off, and the injector be restarted; unless it be of the _self-starting_ variety, which auto-cone,” and allows the injector to ”pick up” of itself

For economy's sake part of the steam expelled from the cylinders of a locomotive is sometimes used to work an injector, which passes the water on, at a pressure of 70 lbs to the square inch, to a second injector operated by high-pressure stea direct from the boiler, which increases its velocity sufficiently to overcome the boiler pressure In this case only a fraction of the weight of high-pressure steaht of water, as coe injector

[1] ”The Steaht of steaht of water A pound of steam, if condensed, would form a pound of water

Chapter II

THE CONVERSION OF HEAT ENERGY INTO MECHANICAL MOTION

Reciprocating engines--Double-cylinder engines--The function of the fly-wheel--The cylinder--The slide-valve--The eccentric--”Lap” of the valve: expansion of stea--Coines--Co-up”--Piston-valves--Speed governors--Marine-speed governors--The condenser

Having treated at soh-pressure steam, we may pass at once to a consideration of the y of steaines are of two kinds:--(1) _reciprocating_, e cylinders and cranks; (2) _rotary_, called turbines

RECIPROCATING ENGINES

[Illustration: FIG 17--Sketch showing parts of a horizontal stearaine C is a _cylinder_ to which steah the _steam-ways_[3] W W, first on one side of the piston P, then on the other The pressure on the piston pushes it along the cylinder, and the force is trans rod_ C R, which causes the _crank_ K to revolve At the point where the two rods uide to prevent the piston rod being broken or bent by the oblique thrusts and pulls which it ih C R to the crank K The latter is keyed to a _shaft_ S carrying the fly-wheel, or, in the case of a loco-wheels The crank shaft revolves in bearings The internal diameter of a cylinder is called its _bore_ The travel of the piston is called its _stroke_ The distance from the centre of the shaft to the centre of the crank pin is called the crank's _throhich is half of the piston's _stroke_ An engine of this type is called double-acting, as the piston is pushed alternately backwards and forwards by the stea rod, and crank lie in a straight line--that is, when the piston is fully out, or fully in--the crank is said to be at a ”dead point;” for, were the crank turned to such a position, the admission of steam would not produce motion, since the thrust or pull would be entirely absorbed by the bearings

[Illustration: FIG 18--Sectional plan of a horizontal engine]

DOUBLE-CYLINDER ENGINES

[Illustration: FIG 19]

[Illustration: FIG 20]

Locoines which must be started in any position have at least _two_ cylinders, and as19 deine is at a ”dead point,” the other, C_2, has reached a position at which the piston exerts the20 each crank is at 45 with the horizontal, and both pistons are able to do work The power of one piston is constantly increasing while that of the other is decreasing If _single_-action cylinders are used, at least _three_ of these are needed to produce a perpetual turning movement, independently of a fly-wheel

THE FUNCTION OF THE FLY-WHEEL

A fly-wheel acts as a _reservoir of energy_, to carry the crank of a single-cylinder engine past the ”dead points” It is useful in all reciprocating engines to produce steady running, as a heavy wheel acts as a drag on the effects of a sudden increase or decrease of steaold-slicer, cake-crusher, or chaff-cutter, the fly-wheel helps the operator to pass _his_ dead points--that is, those parts of the circle described by the handle in which he can do little work