The Governor (Fig. 199) is another ingenious and important invention of Watts, and serves a most useful purpose; it will be understood that if when an engine was working with the full strain of the machinery upon it, the belting was to break, the engine would immediately begin working at an alarming speed, most destructive to itself (this does not apply to engines, such as locomotives, that have constant attention); the governor, as the name implies, controls this. By referring to the illustration, it will be seen that as the speed of the engine increases, the faster the governor rotates (it being connected with the crank shaft); this, by centrifugal action, makes the two balls fly out, and this causes a valve in the steam inlet to partially close and so check the supply of steam from boiler to engine, thus very naturally reducing the speed.
Lubricators (self-acting) are provided wherever necessary, and it is important that a motor of any description be well lubricated at its wearing parts or wherever friction takes place; this reduces the wear and tear to a minimum, and very greatly adds to the motor’s efficiency.
Steam is produced by subjecting water to heat, and so causing it to evaporate; steam is commonly understood to be (by those that have not studied the subject) a white watery vapour, whereas it is exactly the reverse, it is practically as dry and colourless as the atmosphere, and possesses similar characteristics in its unlimited expansibility and compressibility; it only assumes the white vapoury appearance when it escapes in the air which is at a lower temperature than itself, as it then condenses into its original form, water; if steam was ejected into a compartment that was heated to say 220° the steam would retain its own form and be quite colourless and invisible. The expansive power of steam is put to good purpose in what is known as the “cut-off” and also in compound engines; the cut-off is an arrangement whereby the steam is cut off from the cylinder, when the piston has been impelled ½ or ⅝ of a stroke, and the expansion of the steam completes the stroke. In compound engines (which are large and have 2 cylinders) the steam, after doing service in the first cylinder, is conducted to a second of greater diameter, where by expansion it exerts a lower pressure, but on 2 or 3 times the piston area, so giving units of work equal to the first cylinder. Engines are now made with 3 cylinders, thus fully utilising this economical plan.
Horse-power.—When steam engines first came into use they were applied to work previously done by horses which worked the mills; it was, therefore, convenient and desirable to say what number of horses an engine would supersede, hence the term horse-power, which means a capacity to produce a mechanical effect equivalent to raising 33,000 lb. one foot per minute. The indicated horse-power of an engine is the pressure exerted by the steam on the piston without allowing for friction, the indicated horse-power is therefore higher than the power that will be realised; the nominal horse-power is that which is obtained by measurement of the cylinder and piston area, and is a commercial standard, but a deficient one, and most makers’ lists now show engines which by improvements will give 1 and 2 actual horse-power higher than the nominal.
The makers of steam engines might be named “legion,” but the two following are firms of repute, making somewhat a specialty of small motors. Fig. 200 shows a combined vertical engine and boiler complete with feed pump and water tank base, and requiring no fixing (makers Hindley & Co., 11 Queen Victoria Street, London, E.C.); the boiler is multitubular (vertical tubes) and the sizes vary from 2 to 6 horse-power, costing from 62l., to 122l.; if coal fuel is not available, and it is desired to burn wood, peat or inferior fuel, it is usual to have the boiler a size larger costing from 3l. to 10l. extra. It will be noticed that the water tank forming the base, causes the feed water to become heated. The plan of heating the feed water is now universally followed, as it will be understood how disadvantageous it is to pump cold water into the boiler when it is in full work. Feed pumps are now made to pump boiling water if required. Fig. 201 shows a Hindley’s horizontal steam engine complete with pump, but without boiler, made in sizes from 2 to 15 horse-power, costing from 24l. to 100l.
200. Hindley’s Vertical Engine. 202. Tangyes’ Vertical Engine.
201. Hindley’s Engine.
Fig. 202 is a Tangyes’ (Tangyes, Limited, 35 Queen Victoria Street, London) vertical steam engine and boiler complete, and mounted on a wheeled bed for portability, the cost being 2 horse-power 63l., 3 horse-power 79l. Fig. 203 is a Tangyes’ vertical engine without boiler, and on firm base, price, 2 horse-power 22l., 3 horse-power 29l., including feed pumps.
We have purposely omitted the use and description of condensers, as they are only of real use with very large engines (except with marine engines to which condensers are always fitted as the cold water for condensing is at hand in unlimited quantities); a good use to which the exhaust steam can be put is to heat the feed water; Fig. 204 is a Tangyes’ feed-water heater; it will be seen that the heating medium is the exhaust steam from the engine. These are made with brass tubes, which on account of great expansion and contraction will not permit the incrustation to adhere to their surface, and it falls in a scaley and sandy mass to the bottom where a mudhole and handhole are provided for periodical cleaning; the cost of these varies with the size of the steam exhaust pipe, for a 2 in. pipe the price is 13l.
If the exhaust pipe is carried any distance, it must be thoroughly well insulated, or the steam will condense, and the water will run back into the cylinder; this really occurs to a small extent with the best management, consequently a “steam trap” is used, the object of which is to discharge water resulting from condensation. The management of a small steam motor is practically simple, but moderately constant attention is needed; it must be seen that the supply of water is kept up in the boiler, the water and pressure gauges must be occasionally looked to, and the lubricators must be replenished regularly. The want of skilled attention is felt when a small accident or breakdown occurs, but this of course applies to all motors.