Fig. 3317, 3318Figs. 3317, 3318.
Figs. 3317, 3318.
InFig. 3317it is shown in its simplest form, and inFig. 3318with the driving pulley and speeder (or engine speed regulating device) attached. This speeder consists of a spiral spring whose tension may be adjusted to more or less resist the rise of the governor balls, and thus enable the engine to run at a greater speed for a given amount of rise of the governor balls, hence by increasing the tension the engine speed is increased.
The adjustment of the spring tension is made by a worm actuating a worm wheel on a rod passing through the spring, and to which one end of the spring is attached, the other acting on an arm that projects into a slot in the governor spindle. It is obvious that the speeder can be adjusted while the engine is running.
Fig. 3319Fig. 3319.
Fig. 3319.
InFig. 3319the governor is shown with the speeder and Sawyer’s valve, the latter enabling the governor valve to be opened or closed without affecting the rise and fall of the governor balls, which is done by operating the arm shown on the right, whose ends are provided with loops, so that a cord may be attached, enabling the engineer to operate the governor from a distance.
Fig. 3320Fig. 3320.
Fig. 3320.
The safety stop or stop motion is shown on the right,Fig. 3320.
Fig. 3321Fig. 3321.
Fig. 3321.
It acts to close the governor valve and stop the engine in case the belt that drives the governor should get off the pulley or break. This stop motion consists of a pulley suspended by a rod, and riding on the belt which supports its weight. Should the governor belt break, this pulley falls and severs the connection between the valve and the governor, closing the valve, and holding it closed.Fig. 3321shows the governor in section to expose the construction of the valve. The valvevis what is termed a poppet or poppet valve, which is balanced, because the steam entering ati, and taking the course denoted by the arrows, acts equally on both ends of the valve and does not press it in either direction, while as the steam surrounds the valve it is not pressed sideways.
Atbis a gland or stuffing box to keep the spindle or rod steam-tight. Atais the slot for receiving the arm from the speeder and from the stop motion.
pis obviously the driving pulley, imparting motion to the bevel wheelsg, which drive the outer spindles, the inner spindles′being connected toa. The balls are upon ribbon springsd, which are secured at their lower ends to a link fast to the spindles.
The centrifugal force generated by the balls causes them to move outwards, their upper ends pulling down the cap to which they are secured, and this cap operates the valve.
Governors of this class are sometimes termedfly-ballgovernors.
The method to be pursued before starting a plain slide-valve engine depends upon what the engineer knows about the condition of the engine.
If he knows the engine is in proper running order, all that is necessary is to first attend to the oil cups and start them feeding.
Then, if it is necessary, move the crank into the required position to start it easily; open the waste water cocks to relieve the cylinder of the water that will be condensed from the steam when it enters a cool cylinder, and turn on the steam; giving the throttle valve enough opening to start the engine slowly.
The best position for the crank pin to be in to enable its starting easily is midway between the horizontal and vertical position (or, in other words, at an angle of 45° to the line of centres) and inclining toward the cylinder, so that when the engine moves the piston will travel toward the crank shaft.
There are two reasons why this is the best position for starting.The first applies to all engines because there is a greater piston area for the steam to act on when the piston is moving toward the crank than there is when it is moving away from it. This occurs because the piston rod excludes the steam from a part of the face of the piston. The second applies to all plain slide-valve engines whose slide valves have equal laps and both steam ports of equal widths, because the live steam follows further on the stroke when the piston is moving toward the crank than it does when it is moving away from it, and it follows that more piston power is developed, and the engine is less likely to stop when passing the dead centre.
When first taking charge of an engine, it is proper, before starting it, to ascertain that it is in fair working order.
A complete examination of an engine should include a test of the fit of the piston to the cylinder bore, of the cross head to the guide bars, of the connecting rod brasses to the crank pin and cross head journals, and of the crank shaft to its bearings. It would also include a testing of the alignment of the crank shaft and of the guide bars, as well as the set of the valves and the adjustment of the governor.
The least examination permissible with a due regard to safety would be to move the engine throughout at least one full revolution by hand, and to see that the connecting rod brasses and the main bearings do not fit too tight to their respective journals, and to then start the engine slowly by giving it only enough steam to move it, keeping the hand on the throttle valve so as to be able to shut off steam instantly should it become necessary.
A thorough examination should be made in the following order:
First, slightly loosen the nuts on the crank shaft bearings and also the connecting rod keys.
Then move the fly wheel around until the crank points straight to the cylinder, which will bring the piston up to the outer end of the cylinder bore.
Take off the cylinder cover and also the follower from the piston head, and see that the piston rings are set out to fit the cylinder bore but not to bind it tight. Then bolt the follower up firmly in place again.
Take off the connecting rod and move the piston until it touches the cylinder cover at the other or crank end of the cylinder, and then draw a line across the side face of the cross head guide and on the guide itself.
Put on the cylinder cover and push the piston back until it abuts against it, and then make another line on the cross head guide and the guide bar, and these two lines will show the extreme positions to which the piston can be moved when the connecting rod is disconnected.
Next put on the connecting rod, carefully adjust the keys or wedges, so that the bores of the brasses fit easily to the crank pin and cross head pin, seeing that the oil holes are clear, and that oil will feed properly to the journals.
In making this adjustment it is a good plan, if there is any end play of the brasses on the crank pin, to set up the key or wedge until the rod can just be moved by hand on the pin, by first pulling the rod to one end of the pin, and then pushing it to the other.
In putting on the rod, it will be necessary to move the piston a trifle towards the crank.
In making the adjustment of the crank pin fit to the rod brasses, it is a good plan to drive the key home until the brasses are known to bind the crank pin, and then mark a line across the side face of the key and fair with the top face of the connecting rod strap, to then slacken back the key enough to ease back the brasses to a proper fit, and then mark another line on the key.
The first line will form a guide as to how much to slacken back the brasses to adjust the fit, and the second one will form a guide as to how much the key is moved when making a second adjustment,if one should be found necessary after the engine has been running.
Similarly in adjusting the main bearing boxes to the crank shaft, either the nuts, or what are called leads, may be taken to adjust the fit. Leads are necessary when the joint faces of the brasses do not meet, but are left open so that the wear can be taken up while the engine is running.
It is better, however, to let the brasses abut together, so that it may be known that the fit is correct when the nut is screwed firmly home.
The method of taking a lead is as follows: The top brass is loosened, and between the joint faces of the brasses or boxes on each side of the shaft a piece of lead wire is inserted. For a shaft of, say, four inches in diameter, the lead wire will be about7⁄16inch in diameter, or for a 10 inch shaft the wire should be1⁄8inch in diameter, and should be as long as the brass. The nuts are then screwed firmly home, and the wire will be squeezed between the brasses and thus flattened on two opposite sides, the thickness showing how far the joint faces of the brasses are apart when the bore grips the journal.
A liner, fit strip, distance piece, or shim (all these names meaning the same thing) is a strip of metal placed between the joint faces of the brasses to hold them the proper distance apart to make a working fit of the journal and brasses, when the latter are firmly bolted up.
The fit of the top brass therefore depends upon the fit strip being of the proper thickness from end to end.
Now the lead wire is the gauge for the thickness of the fit strip, the latter being made a trifle thicker than the flattened sides of the lead.
If the lead is thicker one end than the other, or if one lead is thicker than the other, the fit strips must be made so, and the leads must be marked so that it may be known which way they were placed between the brasses so that the proper fit strip may be on the proper side of the brass, and the proper end towards the crank.
Another method that is adopted in the case of large brasses is to screw down the nuts until the brasses bind the journal, and then make a mark on the nut and on the bolt thread. The nut is then slackened back as much as the judgment dictates, and a note made of how much this is, the marks forming a guide.
As the wear takes place, and the nuts screw farther down, a new mark is made on the nut, so that it may always be known how much to screw up or unscrew the nut, to make a light adjustment.
To avoid heating, it is a good plan to press some tallow into the bottom or in one corner of the oil cup, and then pour in the oil used for ordinary lubrication. So long as the bearing remains cool, the oil will feed and the tallow remain.
If the bearing heats, the tallow will melt, and, having a heavier body, will give a more suitable lubrication.
To find if the connecting rod is of the right length to give, as it should do, an equal amount of clearance (or space between the piston and the cylinder cover) at each end of the stroke, move the fly wheel a trifle in either direction, and then move it back until the crank is on the dead centre, and draw a line across the cross head guide and guide bar, and the distance between this line and that drawn when the connecting rod was disconnected, shows the amount of clearance at that end of the cylinder. Then move the crank pin over to its other dead centre, and mark a line across the cross head guide and the guide bar, and the distance between this line and that drawn before the connecting rod was put on will show the clearance at this end of the cylinder.
If the clearance is not equal for the two ends, it should be made so by putting liners behind the connecting rod brasses so as to lengthen or shorten the connecting rod (according as the case may require), and equalize the clearance, while at the same time bringing the connecting rod keys up to their proper heights.
To test the set of the valve, the steam-chest cover must be taken off, the crank placed alternately on each dead centre, and the lead measured for each port.
An unequal or an equal degree of valve lead may be given by suitably altering the length of the eccentric rod, but when the lead is equal for the two ports, its amount must be regulated by moving the position of the eccentric upon the crank shaft.
Squaring a Valve.—A method not uncommonly pursued in setting a valve is to what is calledsquare itbefore trying it.
This squaring process consists in so adjusting the length of the eccentric rod that the valve travels an equal distance over or past the steam edge of each steam port; but since the valve does not, when set to give equal lead, travel equally past each port, therefore the work done in squaring a valve is all thrown away, and may result in altering the eccentric rod from its proper length to an improper one, necessitating that it be altered back again in order to set the lead right.
The proper method is to adjust both the length of the rod and the position of the eccentric, by testing the lead at once, lengthening the eccentric rod to increase the lead at the crank end, or vice versa.
Each alteration of eccentric position may render necessary an alteration of rod length, or vice versa, each alteration of rod length may render it necessary to alter the eccentric position, hence the lead should be tried at both ends of the cylinder after each alteration of either rod length or eccentric position.
In vertical engines the weight of the crank shaft causes it to wear the bottom brass or part of the bearing box the most, thus lowering its position, while the eccentric straps and pins wear most in the same direction; hence the wear increases the lead at the head end of the cylinder when the latter is above the crank, and at the crank end when the crank is above the cylinder.
When the cylinder is above the crank, the weight of the piston, cross head and connecting rod is counterbalanced at the end of the downward piston stroke by giving the crank end port more lead; but when the cylinder is below the crank, it is the head end port that must be given increased lead to prevent a pound or knock, or to allow for the wear downwards of the parts.
After an engine is started, the pet cocks should (if they are not automatic) be closed as soon as dry steam issues, and if this cannot be seen, it may be assumed to occur after the engine has made about 20 revolutions.
The parts that will then require particular attention are the crank pin, main bearings, cross head guides and the pump, if there is one. The former must be kept properly lubricated, so that they may not get hot and the cylinder lubricator (which is usually placed on the steam pipe) must be set to self feed properly.
If the crank shaft bearings should begin to heat, loosen the cap bolts and lubricate more freely, or, if it is at hand, some melted tallow may be applied with the oil, as a heavier lubricant may stop the heating.
The crank pin requires the most attention and is the most difficult to keep cool and to examine, because of its circular path rendering it difficult to feel it. This may be done, however, in two ways, first by standing at the end of the engine bed and gradually extending the hand, until the end of the rod meets it as it passes, and, second, by placing the hand on the connecting rod as near to the end of the guide bar as possible where its motion is diminished and moving the hand towards the crank pin, by which means the end of the crank pin may be approached gradually.
If the end of the rod is hot, the engine speed should be reduced or the engine should be stopped so that the connecting rod key or wedge may be eased back and the oil feed made more copious. Then, after the engine has been stopped for the night, the brasses should be taken out and any rough surface, either on the brasses or on the pin, smoothed down with a file.
Hot crank pins may occur from several causes, but by far the most common ones are from improper oiling, or from the engine being out of line.
A heavier oil will often stop, or at least modify, the heating, but its cause should always be discovered and remedied.
Engines that are used out of doors or are exposed to temperatures below the freezing point must be left so that steam leaks may not condense in any of the parts or pipes and burst them.
Leaky throttle valves may, for example, cause water to accumulatein the steam chest and freeze, perhaps bursting the steam-chest cover.
To prevent this let the engine stand with the crank just past the dead centre, so that the steam port will be open, and open the waste water cocks on the cylinder, and also on the steam chest if there is any.
If the cylinder is jacketed all the drain cocks for the jacket should also be opened.
A leaky check valve may cause the steam to condense in the pump and freeze it up solid or burst it or the pipes. To avoid this, open the pump pet cock.
Open all the drain cocks on the heater and water pipes.
If the water is left in the boiler all night it is liable to freeze.
To prevent this leave a well banked fire.
In extreme weather remember that on exposed engines the oil, if of such quality as sperm or lard oil, may freeze and prevent feeding until the bearings get hot and melt the oil.
To prevent this use a lighter oil, as, for example, a mineral oil. Or, in case of freezing, melt the oil in the cups with a piece of wire made red hot while getting up steam in the morning.
A good plan to prevent oil from freezing and yet have a good quality of oil is to mix two parts of lard oil with one part of kerosene.
Portable engines should stand as nearly level as possible, so that the water will stand level above the tubes and crown sheet of the fire box.
When feed water is drawn from a natural supply, as from a stream, the strainer at the end of the suction pipe should be clear of the bottom of the stream, where it is liable to be choked.
When the exhaust steam is used to feed the boiler, do not open the valve that lets the exhaust steam into the feed-water tank until a little while after the engine has started, because the oil fed to the cylinder will otherwise pass into the feed tank and may cause priming.
In engines having plunger pumps for feeding the boiler it is essential to keep the plunger properly packed, as a leak there impairs or stops the pump from acting.
A gauge glass may be cleaned when the engine is cold by shutting off the cocks leading from the boiler and filling the glass with benzine, allowing it to stand two hours; the benzine must be let out at the bottom of the glass tube, and not allowed to enter the boiler.
In starting a new engine be careful to let the bearings be slightly loose.
At first give only enough steam to just keep the engine going, and keep the hand on the throttle valve ready to shut off steam instantly if occasion should require.
Pumps are divided into the following classes:
Lift pumps, in which the water flows freely away from the pump, which performs lifting duty only.
Force pumps, which deliver the water under pressure.
Plunger pumps, in which a “plunger,” or “ram,” as it is sometimes termed, is used.
Piston pumps have a piston instead of a plunger.
A double acting pump is one in which water enters into and is delivered from the pump at each stroke of its piston or plunger, or, in other words, one in which, while water is being drawn in at one end of the pump, it is also being forced out at the other.
A single acting pump is one in which the water enters the pump barrel during one piston or plunger stroke, and is expelled from the pump during the next stroke, hence the action of the suction and of the delivery is intermittent, although the pump is in continuous action.
For very heavy pressures plunger pumps are generally used, the plunger being termed aram.
The advantage of the plunger or ram is that it gives a positive displacement, whereas in a piston pump a leaky piston permits the water from the suction side to pass through the leak in the piston, to the delivery side.
Piston pumps possess the advantage that there is less difference between the contents of the pump and the displacement than is the case in plunger pumps.
The displacement of a piston pump is found by multiplying the area of the pump bore by the length of the piston stroke.
The displacement of a plunger pump is less than the above, by reason of there being a certain amount of clearance or space between the circumference of the plunger and that of the cylinder bore.
It is desirable to keep the clearance space in all pumps as small as the conditions will allow, especially if the pump is liable to lose its water.
Losing the water means the falling of the suction water back into the source of supply, which may occur when the engine has to stop temporarily, and there is a leak in the suction valves.
Fig. 3322Fig. 3322.
Fig. 3322.
Rotary pumps are those in which the piston revolves, an example of the most successful form of rotary pump being shown inFig. 3322, which is that used by the Silsby fire engine.
The advantage possessed by a rotary pump is that it keeps the water passing through the suction in a continuous and uniform stream, as it has no valves.
It may therefore be run at a high velocity or attached direct to the engine shaft.
If a rotary pump leaks, the efficiency is not impaired so much as in a piston or plunger pump, all that is necessary being to run the pump at a high speed.
Fig. 3323Fig. 3323.
Fig. 3323.
The principles of action of a pump may be understood fromFig. 3323, which represents a single acting plunger pump shown in section, and with the suction pipe in a tank of water, the pump being empty.
The surface of the water in the tank has the pressure of the atmosphere resting upon it, and as the pump is filled with air, thesurface of the water within the pipe is also under atmospheric pressure.
Now suppose the plunger to move to the right, and as no more air can get into the pump, that already within it will expand, and will therefore become lighter, hence there will be less pressure on the surface of the water within the suction pipe than there is on the outside of it, and as a result the water will rise up the pipe, not because the plunger draws it, but because the air outside the pipe presses it up within the pipe.
Fig. 3324Fig. 3324.
Fig. 3324.
The water inside the pipe will rise above that outside in proportion to the amount to which it is relieved of the pressure of the air, so that if the first outward stroke of the plunger reduces the pressure within the pump from 15 lbs. to 14 lbs. per square inch (15 lbs. per square inch being assumed to be its normal pressure), the water will be forced up the suction pipe to a distance of about 21⁄4feet, because a column of water an inch square and 21⁄4feet high is equal to 1 lb. in weight. InFig. 3324the pump plunger is shown to have moved enough to have permitted the water to rise above the suction valve, and it will continue to rise and enter the pump barrel as long as the plunger moves to the right.
When the plunger stops, the suction valve will fall back to its seat and enclose the water in the pump; but as soon as the plunger moves back to the left hand and enters the barrel pump further, the delivery valve will rise, and the plunger will expel from the pump a body of air or water equal in volume to the cubical contents of the plunger, or rather of that part of it that is within the barrel, and displaces water.
If the plunger was at the end of its first stroke to the right and the pump half filled with air, then this air will be expelled from the pump before any water is; whereas if the pump was filled with water, the latter only will be delivered.
Now suppose the first plunger stroke reduces the air pressure from 15 to 14 lbs., and that the second drawing stroke of the plunger reduces the air pressure in the pipe to 13 pounds per inch, the water will rise up it another 21⁄4feet, and so on until such time as the rise of a column of water within the pipe is sufficient to be equal in weight to the pressure of the air upon the surface of the water without; hence it is only necessary to determine the height of a column of water that will weigh 15 lbs. per square inch of area at the base of the column to ascertain how far a suction pump will cause water to rise, and this is found by calculation or measurement to be a column nearly 34 feet high.
It is clear then, that however high the pump may be above the level of the water, the water cannot rise more than 34 feet up the suction pipe, even though all the air be excluded from it and a perfect vacuum formed, because the propelling force, that is, the atmospheric pressure, can only raise a column of water equal in weight to itself, and it is found in practice to be an unusually good pump that will lift water thirty feet.
Fig. 3325Fig. 3325.
Fig. 3325.
Fig. 3325shows the plunger making a delivery stroke, the suction valve being closed, and the delivery valve open where it will remain until the plunger stops.
To regulate the quantity of water the pump will deliver in cases where it is necessary to restrict its capacity, as in the case of maintaining a constant boiler feed without pumping too much water in the boiler, the height to which the suction valves can lift must be restricted, so as to limit the amount of water that can enter the pump at each drawing stroke.
The delivery valve should lift no more than necessary to give a free discharge without causing the valve to seat with a blow; but if the pump has a positive motion, the delivery valve must open wide enough to let the water out, or pressure enough may be got up in the pump to break it.
A check valve is merely a second delivery valve placed close to the boiler and serving to enable the pump to be taken apart if occasion should arise, without letting the water out of the boiler.
The lift and fall of both valves act to impair the capacity of the pump. Thus, while the suction valve is falling to its seat, the water already in the pump passes back into the suction pipe, and similarly, while the delivery valve is closing, the delivery water passes back.
A foot valve is virtually a second suction valve placed at the bottom or foot of the suction pipe.
The capacity of a pump is from 70 to 85 per cent. of the displacement of the plunger or piston, and varies with the speed at which the plunger or piston runs.
If a pump runs too fast, the water has not sufficient time to follow the piston or plunger, especially if the suction pipe has bends in it, as these bends increase the friction of the water against the bore of the pipe.
The speed of the piston or plunger should not exceed such as will require the water to pass through the suction pipe at a speed not greater than 500 feet per minute, and better results will be obtained at 350 feet per minute.
An air chamber placed above the suction pipe of any pump causes a better supply of water to the pump by holding a body of water close to it, and by making the supply of water up the suction pipe more uniform and continuous. Air chambers should be made as long in the neck as convenient, so that the water in passing through the pump barrel to the delivery pipe could not be forced up into the chamber, as, if such be the case, the air in the chamber is soon absorbed by the water.
Belt pumps are more economical than independent steam pumps, because the power they utilize is more nearly the equivalent of the power it takes to drive them, whereas in steam pumps there is a certain amount of steam, and therefore of power, expended in tripping the valves and in filling the clearance spaces in the cylinder. Furthermore, the main engine uses the steam expansively, whereas the steam pump does not.
InFig. 3326is shown a modern freight locomotive, the construction being as follows:
For generating the steam we have the boiler, which at the front end is firmly bolted to the engine cylinders, which are in turn bolted to the frames, while at the back end the boiler is suspended by the linksb(one at each end of the fire box on each side of the engine).
The starting bar is shown in position to start the engine, and it is seen that the rodaand bell crankbare in such a position as to open the valvet, and thus admit steam from the dome to the pipee, whence it passes through pipesf,gandrinto the steam chesti, the slide valvevdistributing the steam to the cylinder. The exhaust occurs through the exhaust portd, whence it passes up the exhaust pipe and out at the smoke stack.
The boiler is fed with water as follows:
Thefeed pipe from the tendersupplies water to the injector, which is forced by the injector through thefeed pipe to boilerand into the latter.
In the figure the parts are shown in position for the engine to go ahead, hence the reversing gear is in the extreme forward notch of the sector, and the valve gear is in full gear for the forward motion.
The levermis for opening and closing the cylinder cocks, which are necessary to let the water of condensation out of the cylinder when the engine is first started and the cold cylinder condenses the steam.
To supply steam to the injectors (of which there are two, one on each side of the engine) and to the steam cylinder of the pump, there is a steam pipe leading from the dome to the steam drum, the pipeksupplying steam to the injector, and pipejsupplying steam to the steam cylinder of the air pump. The pipe for supplying oil to the slide valve and cylinder is furnished with a sight feed oil cup, the oil being carried by steam from the steam drum.
This pipe passes beneath the lagging until it reaches the smoke box, which is done to keep it warm and prevent the oil from freezing, while the steam pressure enables the oil to feed against the steam pressure in the steam chest.
The slide valve is balanced by means of strips let into its back, and bearing against a plate fixed to the steam chest cover.
The frame on the side of the engine shown in the engraving is shown broken away from the yokeato the fire box, so as to expose the link motion to full view, the shaded portion of the frame being that on the other side of the engine.
The yoke or braceacarries one end of the guide bars. The safety valvesmay be raised to see that it is in working order, or to regulate the steam pressure, by the levero, which has a ratchet tongue engaging with the notches atl.
Fig. 3326aFig. 3326a.
Fig. 3326a.
Fig. 3326bFig. 3326b.
Fig. 3326b.
In addition to the safety valve with spring balance, however, a pop safety valve is employed on the part of the dome that is shown broken away, the construction of this pop valve being shown in the outside view,Fig. 3326a, and a sectional view,Fig. 3326b, the casing being removed from the latter. In the valve seatbis a recessa, and upon the circumference of the valve is a threaded ringc′. When the valve lifts, the steam is somewhat confined in the annular recess of the valve, and the extra valve area thus receiving pressure causes the valve to lift promptly and the steam to escape freely. The degree of this action is governed as follows:
The sleevec′is threaded upon the upper part of the valve, so that by screwing it up or down upon the valve the amount of opening between the annular recessa a, and the lower edge of the sleevec′ c′, is increased or diminished at will; the less this opening, the more promptly the valve will rise after lifting from its seat.
To secure the sleeve or ring in its adjusted position, the ends of the screwsl,lseat in notches cut in the upper edge of the sleeve. In many engines pop valves alone are used, and in some cases levers are provided by means of which the pop valve can be raised from its seat to test if it is in working order.
Referring again toFig. 3326,his the handle for operating the injector, andwa rod for opening the injector overflow.
We now come to the automatic air brake; steam for the steam cylinder of which, is received from the steam drum through the pipej, passing through the pump governor, or regulatorg. The exhaust pipe for the steam cylinder of the air pump passes into the smoke box. The air cylinder receives its supply of air through the small holes atk,k, and delivers it through the pipecinto the air reservoir or tank, from which it passes through the tank pipe up to the threeway cock or engineer’s brake valve, whose handle is shown atm. The brakes are kept free from the wheels and out of action so long as there is air pressure in the air reservoir and in the train pipe, hence the normal position of the handlemis such as to let the air pass from the air reservoir up the pipexand into the train pipe. When the brakes are to be applied, handlemis moved so that there is an open connection made between the train pipe and thepipe to openair, which releases the air pressure and then puts on the brakes not only on each car, but also on the engine, because the engine brake cylinders receive their air pressure from the pipe shown leading to the train pipe. From the tank pipexa pipehleads to the top of the pump governorg, whose action is to shut off the steam from the steam cylinder of the air pump whenever the pressure in the air reservoir or tank exceeds 70 lbs. per square inch. A small pipe leads up from pipehto the air pressure gauge.
For regulating the draught of the fire there is a damper door at each end of the ash pan, and to increase the draught, a pipe leads from the steam drum into the smoke box, where it passes up alongside of the exhaust pipe, its end being shown atz. This is called theblower, and its pipe is on the other side of the engine. The plate shown atp,pin the smoke box checks the draught in the upper tubes, and therefore distributes it more through the lower ones.
Fig. 3327Fig. 3327.
Fig. 3327.
There are two sand valves, both of which are operated by one rod, the construction being shown inFig. 3327, which is a plan showing the bottom of the sand box broken away to expose the gear for moving the valves. The two valvesv,vfor the sand pipes are on raised seatse,e, and are fast on the same shafts as the segmentss,s, but the valves are obviously above, while the segments are beneath the bottom of the sand box. The gear wheelwis pivoted to the under side of the bottom of the sand box, and the armlis fixed to the wheel. Attare pieces of wire, which, being fast in the spindle, revolve with it and stir up the sand when the valves are moved. As shown in the figure, the two sand pipesa,aare open, but suppose the rod is moved endways andlwill revolvew, which will moves,sand the valvesv,v, causing the latter to move over and cover the pipesa,a, and shut off the sand from the pipes.
Largeimage(515 kB).
Fig. 3328represents an American passenger locomotive with a steam reversing gear, or in other words, a reversing gear that is operated by steam.
The link motion is substantially the same as that shown inFig. 3326for a freight locomotive, the eccentric rods in this case being straight, as there is no wheel axle in the way.
The injector for feeding the boiler is the same as that shown on the freight locomotive.
The ash pan is provided with two dampers, one at each end, and the front one is operated by the bell cranka c.
The sand boxes are here fastened to the frame, both sand valves being operated by the leverm, which at its lower end connects to a rod,u, which at its back end connects to an arm,p, on a shaft that extends across the fire box and connects to a rod corresponding to rodu, but situated on the other side of the engine and connecting with the other sand valve.
The steam pump for the automatic air brake is on the other side of the engine, and the air reservoirs, of which there are two, are horizontal and situated beneath the front end of the boiler. The air pipe to the triple valve here connects to the front pipe of the three beneath the triple valve, the middle pipe being that which is open to the atmosphere, which is the usual construction. The engine brake receives its air from a pipe on the other side of the engine which feeds the pipesg,v, for the brake cylinder shown in the figure. When the engine is running backwards, the train brakes are operated through the medium of the “pipe to air brake and to front end of engine” which is shown broken off.
Largeimage(41 kB).Fig. 3328aFig. 3328a.
Largeimage(41 kB).
Fig. 3328a.
The construction of the steam reversing gear is shown inFig. 3328a.ais a steam cylinder andba cylinder filled with oil or other liquid. Each of these cylinders has a piston, the two being connected together by their piston-rodsc c′. These rods are also connected to a leverd e f, which works on a fulcrume. The lower end of the lever is connected to the reverse rodf g, the front end of which is attached to the vertical arm of the lifting or reverse shaft. It will readily be seen that if the piston inbis free to move and steam is then admitted to either end of the steam cylindera, the two pistons will be moved in a corresponding direction, and with them the leverd e f, and the other parts of the reversing gear. A valve,h, is provided, by which communication is opened between the cylinderaand the steam inlet pipe. Another valve,i, is placed betweenhand the cylindera, by which the steam may be admitted either into the front or back end of the cylinder. It will be apparent, though, that if the piston inais thus moved, and the reverse gear placed in any required position, some provision must be made to hold it there securely. This is accomplished by the oil cylinder and pistonb. To it a valve,j, is provided, by which communication between the front and back ends of the cylinder may be opened or closed. It is evident that if the pistonbis in any given position, and both ends of the cylinder are filled with liquid, the former will be held securely in that position if the liquid in one end cannot flow into the other. If, however, communication is opened between the two ends, then, if a pressure is exerted on the pistonb, it will cause the liquid to flow from one end of the cylinder to the other, and thus permitbto move in whichever direction the pressure is exerted.
ris the reverse lever, made in the form of a bell crank, the short end of which works in a slotc, in the upper end of a shaft or spindled. This shaft is inclosed by a tubular shafts, to which the fulcrum ofris fastened. The tubular shaft has an armb. The reverse lever has two movements, the one to raise the end up, and the other to turn on the axis of the tubular shaft. The armbon the latter is connected by a rod,f, with the valvesjandh. The lower end of the shaftdis connected with a bell crank,f′, which, in turn, is connected by a rod,k l, with the valvei. Therefore, by turning the leverrso as to partly revolve the shafts, the valvesjandhmay be opened or closed, and by moving the leverrup or down, the valveiis moved to admit steam to the front or back end ofa. To reverse the engine, therefore, the leverris turned so as to open the valvesjandh. This opens communication between the opposite ends ofb, andhadmits steam toi. Now, by reversing the end of the reverse leverr, the valveiis moved so as to admit steam to either end ofa, the pressure in which will move the reverse gear to the desired position. When this is done, the valvesjandhare closed. This prevents the fluid inbfrom flowing from one end of the cylinder to the other, and thus securely locks the pistonbin the position it may happen to be in, and at the same time the valvehshuts off steam from the cylindera.
The barkis graduated, as shown in the plan ofr,k, to indicate to the locomotive runner the position of the reversing gear.
This apparatus enables the reversing gear to be handled with the utmost facility, and with almost no exertion on the part of the engineer. The engine can be reversed almost instantly, and it can be graduated with the most minute precision.
The link motion of an American locomotive is shown inFigs. 3329and3330. InFig. 3329it is shown in full gear for the forward gear, or in other words, so as to place the engine in full power for going ahead.
The meaning of the term full power is that, with the link motion in full gear, the steam follows the piston throughout very nearly the full stroke.