How should an engine be started?

What precaution should an engineer take before starting an engine?

What course should an engineer pursue when it becomes necessary to stop for any length of time?

What course should be adopted in case of extreme heating in any of the revolving parts of an engine?

How should the piston-packing in the cylinder be treated?

What are the best means of protecting the cylinder and steampipes from the effects of the atmosphere in order to diminish radiation and condensation?

What course should be adopted when a clicking sound is heard in the cylinder?

Why is it very important that the steam pressure should be kept uniform?

Give the reasons why the piston- and valve-rod packing is so frequently out of order.

Explain the best method of using piston- and valve-rod packing.

What is the best course to adopt when excessive leakage occurs?

How should piston- and valve-rod packing be kept?

Give the rule for finding the right diameter of packing for any stuffing-box.

What is the object of lubrication?

What effect has temperature on lubricants?

What conditions influence the amount of lubrication required for any engine?

PART FOURTH.

The Steam-Engine Indicator: Its Invention and
Improvement.

Perhaps no device, in the entire range of mechanical inventions, has aided so much in developing and perfecting the steam-engine

as the indicator.

This arises from the fact that no other invention yet brought forward pertaining to the science of steam engineering can read the inner workings of a steamengine, point them out with unerring accuracy, and dis

cover the sources of

quently, its importance cannot be too highly estimated, and its use too much encouraged and extended in all classes

of steam-engines. P

The steam-engine indicator is said to have been invented by James Watt, which is rather doubtful; and, as Watt received credit for many things he never invented, it is not to be wondered at that the invention of the indicator has been attributed to him. Be that as it may, Watt's indicator, though very im

perfect, answered for engines travelling at a piston speed of about 150 feet per minute, and for pressures averaging 7 lbs. above atmosphere, which he thought was the fastest speed and the highest pressure that would ever be needed. But experience soon demonstrated that the highest economy was attained with high piston speeds and correspondingly high pressures, and, as a result, Watt's indicator proved to be unsuitable for these conditions. The requirements of such an instrument were more fully appreciated by McNought, of Glasgow. The world is more indebted to him for improvements in the steam-engine indicator than to any one previous to his time.

The indicator was further improved by Hopkinson, Stillman, and others; but these improvements were not in the mechanical design or arrangement of its working parts, but rather in the accuracy and refinement of the workmanship employed in its construction, as the mechanical principles embodied in the Watt indicator were continued in them all. They consisted of an upright cylinder, into which a piston was accurately fitted. To the piston-rod a spiral spring was attached, to resist the steam and the vacuum when acting against it. The pencil was also attached to the piston-rod; the result of which was that the piston, piston-rod, and spring had the same movements as the pencil. With such instruments the vibration of the piston was so great as to render them totally unreliable with fast running engines, or when steam was worked expansively.

Gooch was the first inventor that gave the pencil a greater range of movement than the piston. In his instrument the cylinder was placed horizontally, and when its piston was subjected to pressure it compressed two elliptic springs. The top of his piston-rod was connected to the short arm of a lever, to the long arm of which the pencil was attached, thus giving considerably more motion than could be obtained by any former instrument. The pencil moved in the arc of a circle instead of a straight line. The diagram was traced on a web of paper while it was unwound

from one drum and wound upon another. This arrangement admitted of a succession of diagrams being taken without any intermediate manipulation of the instrument. The communication between the indicator and the steam-cylinder was closed by a slide-valve instead of a cock. But as the principle of working steam expansively became almost universal, an instrument more reliable than any of these previously mentioned became a necessity of the times, and such was found in the Richards' Indicator. In this instrument the following construction and proportions have been adopted, and adhered to from the first. The area of the piston is a square inch, the diameter of which is very nearly of an inch, or, more exactly, '79 inch. The length of the long arm of the lever, to which the rod of the piston is attached, is 3 inches, and the distance from the pivot of the lever

to the point of attachment of the piston is of an inch, thus giving the free end of the lever, and with it the pencil, four times the movement of the piston. The secondary lever is equal in length to the first, and the link which connects the two, and which carries the pencil at its centre, is 17 inches long. These propor

22

tions give a practically straight pencil movement for a distance of 24 inches.

The indicator was further improved by Harris Tabor, (cuts of whose instrument may be seen on pages 260 and 261;) but

more recent improvements made in the indicator have been effected by George H. Crosby, a mechanical engineer of Boston, Mass. It has apparently been the aim of Mr. Crosby to avoid unnecessary weight in the reciprocating parts, to insure correctness of action, and to so simplify the method of manipulating the instrument as to bring it within the understanding of engineers of limited education and persons of ordinary intelligence. In these objects he seems to have been partially successful,

as the Crosby Indicator is an improvement, in some respects, on other devices of the kind in use; as it is reliable in its recordings, whether employed for taking diagrams from automatic cut-off, throttling, simple, compound, fast- or slow-run