136. In fig. 135, f is the great spurwheel, corresponding to i, fig. 133, which gives motion to all the internal machinery. It has a small bevelled wheel on its shaft, which moves the small inclined shaft g, giving motion to the feeding-gear h, which moves either from 45 to 50, or from 65 to 70 rotations in a minute, according as the straw is wished to be taken in fast or slow; but the immediate action of the great spur-wheel ƒ is on the pinion i, which is placed on the shaft of the drum, and moves it and as the two wheels have a great disparity of size, it will be easily understood that the drum moves at a high velocity, which is not less than 360 revolutions in a minute, and the spur-wheel 50 rotations. A small pinion on the spurwheel shaft, gives motion to the intermediate wheel k, which drives the wheel 7 on the shaft in the first shaker. The two intermediate wheels m m are required to move the wheel n of the second shaker, and to give it a contrary motion to the first shaker. Instead of such wheels, a small wheel on the shaft of the spur-wheel f, is sometimes made to move the feedinggear, and both shakers, by means of pitchchains; but although this is a simpler, and perhaps cheaper construction than the other, it is much more likely to go out of working order. 1695. The description of the machine is as far advanced as to enable you to trace the progress of the straw through the machine. The spur-wheel ƒ moves from right to left to give the beaters i' of the drum i, fig. 136, a motion from left to right, that is, they shall beat the straw in an upward direction. The sheaves of corn are placed in the feeding-board e, and are taken from it by the rollers of the feeding-gear h', and retained hold of Fig. 136. while the beaters of the drum, passing in an upward direction, separate the corn from the straw, which are both prevented being driven upwards into the air by the drum-cover i On the straw being carried over the top of the drum, it is drawn by its force towards the first shaker l, and throws it towards the second shaker n, which lifts it over itself, and throws it down upon the straw screen o', upon which it slides further down to the floor of the straw-barn. The shakers have a lower velocity than the spur wheel. 1696. The corn passes through the machine in this manner :-The straw and corn pass together over the top of the drum i, and are raked together by the shaker, near the screen l', through which the corn immediately falls into the hopper o, descends still farther upon the vibrating shoe of the fanners p, and on falling still farther, from which the wind, created by the fan, separates the chaff from the corn, carrying the former into the chaffhouse, and allowing the latter to pass through the spout to the floor of the corn-barn. As much of the corn as passes over the ridge m" between the two shakers l and n, is met by the brushes of the shaker n, which sweep it clean off the board n' towards the screen m', through which it falls into the hopper o and fanners p, in company with that passed through at first through the screen l'. 1697. The fan of the fanners is moved by means of a leathern belt or a hempen rope q q, fig. 135, which is given motion to by a sheave on the shaft of the drum, and carried by a couple of sheaves at r, one of which conveys the rope down to the sheaves, on the spindle of the fan, and the other carries it back again to the drum. The sheaves is composed of sheaves of different diameters, to allow the fan to be driven at different velocities, according to the state and nature of the corn to be cleaned, and its spindle is supported at one end by the upright post t. The velocity of the fan is 220 rotations per minute. 1698. The thrashing-machine is set in motion by different kinds of power,-by steam, by horse-strength, by the wind, and by water. Of these, wind power is getting more and more out of use in driving farm machinery, on account of the great uncertainty attending the motions of so fickle an element, in so variable a climate as ours; and every day, as the management of the steam-engine is more and more understood, it is becoming more in use on farms. Where water is sufficiently abundant, it is the simplest, as well as the cheapest, of motive powers, and. is always preferred to all others; but where the supply is insufficient, although it may be ample enough for a time in winter, it partakes of the disadvantages attending wind,-it may be insufficient at the time it is most wanted. Experience has abundantly proved that thrashingmachines dependent on water derived chiefly from the drainage of the surface of the ground, frequently suffer from a short supply in autumn, and late in spring, or early in summer, thereby creating inconvenience for the want of straw in the end of autumn, and the want of seed or horsecorn in the end of spring. Wherever such casualties are likely to happen, it is better to adopt a steam-engine at once. Although coal should be both distant and dear, for all that a steam-engine requires, a steamengine should be erected in preference to using horses in the thrashing-machines; for besides having to keep a larger number of horses on a large farm, in the proportion of one pair in every five pairs, the tear and wear of horses in the rotary motion of the horse-course is very considerable. 1699. Of the three classes of steamengines, the atmospheric, the low, and the high pressure, the high pressure is most commonly used on farms, partly from the notion that it requires less water, is more simple in its construction and management, and cheaper than the condensing or low pressure engine. It is certainly very simple in its construction, and its management is easily understood, even by country people, and it is generally less costly than the condensing engine; but a sufficient reason for the preference may be found in the fact, that an engine from four to six horse power is quite sufficient to move most thrashing-machines, whereas the condensing engine is better applicable to purposes requiring a higher scale of power. 1700. The high-pressure steam-engine is so called because the steam is generated in the boiler, at so great a degree of tension as to exert a considerable pressure on the boiler,-not less, perhaps, than 25 lbs. to the square inch, and it may be increased to a much higher rate without difficulty; that is, the pressure on the interior of the boiler above that of the atmosphere on its exterior, which is equal to 14 lbs. to the square inch. It is also called non-condensing, because it gets quit of the steam in the elastic state, and is not condensed again into water as in the condensing engine. And it is some times called the puffing engine, because it emits the steam it has used in successive jets or puffs. 1701. Crank high-pressure SteamEngine.-The high-pressure steam-engine may be formed with a beam or an overhead crank, besides a variety of other forms; but these two are the forms found on the farm, and of these the crank engine is the most common, and it is on this account that I have selected its figure for illustration. It is represented in fig. 137, where bb is the ground floor, cc the sole plate, which is bolted down to a mass Fig. 137. to preserve its parallelism; the end of the lying shaft is seen at the letter k; mm is the fly-wheel; and the small circle at i is one of the balls of the governor. The steam-pipe leading from the boiler joins the engine at n, from whence the steam descends to o, and passing through that branch, and the throttle-valve case p, it enters a channel that half embraces the cylinder, and opens into a small steamchest that contains the slide-valve, which are concealed behind the cylinder in the figure. The steam-chest covering the slide being thus in communication with the boiler, the steam, from its elasticity, is always ready to flow into any channel that is opened for it. Hence, as the slide is moved alternately from off the passage leading to the upper and to the lower ends of the cylinder, the piston is made to reciprocate between the top and bottom. At every change of the slide, the passage leading to the atmosphere is put in communication with the top or with the bottom of the cylinder, and the steam which had, in the previous stroke, done its duty on the piston, is drawn off and discharged through a channel corresponding to that by which it entered, and passing through the branch q, into the column qr, it is discharged into the atmosphere by the pipe r, which frequently terminates in the chimney. The crank-shaft carries two eccentrics-the one for the pump-rod, to which is jointed the plunger of the pump, for supplying water to the boiler; the other moves the slide-valve rod, which is so adjusted as to move the valve at the precise time and place required for the due admission and emission of the steam to and from the cylinder. The shaft likewise carries the pair of level wheels that give motion to the governor. The governor consists of two oblique rods, with balls attached to their lowest extremities; and these being suspended by a joint on the vertical axis, the whole is rendered capable of revolving horizontally upon that axis. If the machinery that gives motion to the governor is accelerated, the revolving balls partake of the acceleration, and the centrifugal action thus generated gives them a tendency to fly off from the centre of revolution. This outward motion is converted into the means of regulation, for while the balls and rods extend their circle of gyration, they act upon two jointed arms. The lever is applied to the collar above the joint of the rods, and being suspended near its centre, has its opposite extremity jointed to the rod x, the lower end of which acts upon the lever of the throttle-valve s. The throttle-valve is a thin circular plate of metal, having an axis fixed across its diameter, and is nicely fitted into the steam-way passing through the case p. The spindle passes the sides of the case steam-tight, and carries on one end a small lever by which the valve can be turned, and the lever is put in connexion with the lower end of the rod a. The extension of the balls of the governor, acting through the lever w and rod a, depresses the lever s of the valve, and by thus turning the valve, reduces the steam-way, and prevents further acceleration of the machine. 1702. In setting down the engine, we have to consider the space necessary to receive it. This, in the direction of the barn wall, need not be larger than 81 feet, or a few inches more than the diameter of the fly-wheel; the breadth, in the other direction, should not be less than 8 feet, but may extend to 9 or 9 feet. An engine-house, therefore, of the form and dimensions afforded by the plan Plate II., is not well adapted to this form of engine, its length in the direction of the barn being too great for the entablature beam; and if adopted for such a form of house, a wall must be run up, or a beam placed across, reducing its length to 8 feet, or thereby. In almost every case this form of engine is the most commodious for its application to a thrashing-machine, especially in regard to the direction of height; for the height that the crank-shaft stands above the floor of the engine-house will generally bring it near to the large spur-wheel, which, though not in all thrashing-machines, is yet to be found in a large majority of them. This is supposing that the floor of the engine-house is nearly on a level with the barn floor, which will generally be the case, unless artificially changed. 1703. Mr Slight has given this rule for finding the horse-power of such a noncondensing engine: Multiply the square of the diameter of the cylinder in inches, by sixth-tenths of the entire pressure of the steam in the boiler in lbs., on the circular inch, minus half an atmosphere, or 5.57 lbs., on the circular inch; and multiply the product by the velocity of the piston, in feet per minute. The last product is the power of the engine in lbs. to raise one foot high per minute; and for the horse-power divide as usual by 33,000. For example, Let the cylinder be 9 inches diameter, the length of stroke 20 inches, and the number of strokes per minute 64, being equal to a velocity of 214 feet per minute for the piston, and the pressure in the boiler 25 lbs. on the circular inch, equal to 32 lbs. on the square inch nearly; then (6 × 25 — 5·75 9.35; and = 9.2 x 9.35 x 214 = 5-horse power nearly. 33,000 By this rule for the power of non-condensing engines, a cylinder of 10 inches diameter, with a pressure of 25 lbs. on the circular inch, and making 60 strokes per minute, is equal to 6-horse power; and the piston will move at a velocity of 214 feet per minute, making the consumpt of steam, allowing for waste, equal to 128 cubic feet per minute, or 7680 per hour. The proportion of water to steam consumed at this pressure, is about 1 to 850, or a little more than 9 cubic feet of water, being about 57 gallons per hour for the supply of the boiler. This calculation is stated merely to show how small the quantity of water is that suffices for a non-condensing engine of 6-horse power. 1704. The setting on and stopping the non-condensing engine is an exceedingly simple operation; and its simplicity is even simplified by the addition of a cock or valve on the steam-pipe, which is very frequently adopted, and in that case the throttle-valve is not required to be so accurately fitted as where no stop-cock is employed. To set on the engine, the steam must first be brought up to the requisite degree of pressure. When this is accomplished, which is known by the safety-valve rising so as to allow the escape of steam, the stop-cock, if there is one, is opened, the throttle-valve being also opened; the steam is admitted both above and below the piston by moving the slide with the handle of the wiper-shaft, to heat the cylinder, the eccentric rod being at the time disengaged from the shaft. This done, the gab of the eccentric rod is laid upon the arm of the wiper shaft; and, if the crank is in a horizontal position, the engine may start off without assistance; but, if it does not move, the fly-wheel is to be pushed round a few feet, or until the crank has once passed the centres, when it will move on freely. If no resistance is upon the engine, the throttle-valve should be put nearly shut, but so soon as the resistance comes,-the commencement of thrashing, for example, the throttle-valve lever is to be connected to the vertical rod, and the work will proceed regularly. 1705. In stopping, where there is a stop-cock, the shutting of it puts a stop to further motion, except what the momentum of the parts may continue to give out for a few seconds; where there is no stop-cock, the first step is to disengage the throttle-valve lever, and close the valve, and immediately after disengaging the eccentric rod from the wiper-shaft, the engine will stop. It is advisable to keep this rod disengaged at all times when the engine is standing. 1706. As the engine-house is seldom accessible directly from the barn, there ought always to be means established for communicating a signal between the two places; and this should proceed from the chief of the operation,-the person who feeds the machine. As there can be but two propositions to make-to set on and to stop one signal is sufficient, and a bell seems to be the most convenient medium of communication. 1707. The boiler.-Of all the parts of the steam-engine, the boiler, though by far the simplest in its construction, is the most important. In it is generated the agent of power, while all the other parts are merely the accessories and media through which the effects of the mighty agent are developed. It has constantly, while in action, to resist this imprisoned and powerful agent, and that merely by the strength of its parts; hence the necessity for having boilers made of the best possible materials, and those connected in the best possible manner. 1708. The form now most generally adopted for the boilers of farm-engines, and it is undoubtedly the best, is the plain |