Modern Machine-Shop Practice Part 254

In order to simplify the explanation, the mechanism has been separated into three separate sections. Figs. 3386 and 3387 show such of the details of the parts between the cylinder and crank as are peculiar to this engine. The cross head is of the slipper guide style, and the ill.u.s.tration, Fig. 3386, shows the simple method adopted for adjusting the guide to the proper height to maintain the alignment. Another feature peculiar to the straight line not mentioned above, that of making the cross head pin fast in the connecting rod, is used in this engine also, but in a somewhat different form. As will be seen by Fig.

3387, the pin is made much larger, and this allows of its being made of "steel casting" and cast hollow with cross bars at each end for centring. These pins are held in the rod by a binding screw which catches in a groove that is milled around one-fourth of its circ.u.mference. After the pin is placed in the rod and the binding bolt is inserted, the pin is prevented from working out endwise, and the binding bolt prevents it from turning; but when the binding bolt is slackened, the pin can be rotated one-fourth of a revolution. The scheme is as follows: After running the engine for a while, the engineer is instructed to slack the binding bolt, give the pin a quarter turn and bind it fast. By repeating this, the pin can be kept more nearly round, probably, than by any other plan. By referring again to Fig. 3386, it will be seen that the plan for taking up the wear in the cross head pin bearings is simply that of setting up the common half box, and the endurance of the arrangement, with the hardened and ground steel pin running in babbitt lined boxes of double the ordinary size and length, must be satisfactory.

[Ill.u.s.tration: Fig. 3387.]

The drop oil cups for lubricating the cross head pin are located so as to have the drop "picked" off just as the cross head completes its stroke at the cylinder end, and while it is travelling at its slowest speed. The oil, as it leaves the wearing surfaces of the pin, is conveyed to the lower slide.

[Ill.u.s.tration: Fig. 3388.]

[Ill.u.s.tration: Fig. 3389.]

Figs. 3388 and 3389 show the parts that connect the eccentric with the valve. The method of connecting the rod to the eccentric strap is convenient. The lower joint in the eccentric strap is set up tight, metal to metal, and the upper joint left open 1/8 of an inch.

STEAM FIRE ENGINE.

In a steam fire engine the prime requisites are rapidity of getting up steam and efficiency with lightness, economy of fuel being a secondary consideration.

Fig. 3390 is a general view of a steam fire engine constructed by the Clapp & Jones Manufacturing Company.

Fig. 3390_a_ is a longitudinal section through the boiler and one steam cylinder and pump.

The construction of the boiler is shown in Figs. 3390_a_ and 3391, the former being a vertical section of the engine and boiler bearing the steam pipe and exhaust pipe shown in place, and one of the draught tubes shown in section, and the latter a vertical central section.

The outside sh.e.l.l is represented at _a"_, _a"_. This sh.e.l.l extends the whole length of the boiler. The fire box sheet _b"_, _b_ is less in length, extending only to the lower tube sheet.

The lower tube sheet C" is perforated by all the tubes; the heavy lines showing the coil tubes in fire box, the others are smoke tubes. The upper tube sheet _d_ has holes only for the smoke tubes. The smoke or draught tubes are shown at _e"_, _e"_, _e"_; these also answer the important purposes of drying and superheating the steam.

F", F", F" are the sectional coil tubes, the main feature of this boiler. They are in the form of a spiral coil, the spiral bend being enough to leave room for five others of the same size between, so that there are six of these coils in each circular row. The number of rows is determined by the size of the boiler and the amount of steam required.

Each coil is connected with the lower tube sheet by screw joints, all right hand, that require no fibrous or elastic packing, an angle elbow being used to get the short bend at the end. The tubes then make about one turn around the fire box, and are joined to the side sheet of the same, with the same union used at its upper end, which makes a joint that never gets loose from any kind of work it may be subjected to.

These unions or couplings are made of different kinds of metal, and put together so that no two pieces of iron come in contact to corrode and stick together; and should it, from any cause whatever, become necessary to take these coils out, it can be done, and the same tubes replaced without destroying any part of them, or damaging any piece so that it could not be used again.

G", G" is the ornamental dome or covering for the upper end; _g"_, _g"_ is the smoke bonnet and pipes for concentrating the hot escaping products of combustion for the purpose of making a draught of air through the fuel. H" are grate bars, and I" fire door. J", J" is the water line. The height has been determined by experiment, yet should be varied a little to get the best drying effect of the coal. A coal that makes a flame would call for a higher range of the water line, while coal that produces heat without the flame would call for a lower range; this the engineer will soon find. The working of the boiler is as follows: The fire being started in the fire box, as soon as the water in the coils begins to heat circulation commences from natural causes (nor is it at any time necessary to use a hand pump or any other artificial means for keeping it up), the heated water pa.s.sing up in the steam drum, and the colder water from the leg and drum taking its place, as is shown by the arrows in the leg, till the whole is heated to the steam making temperature. At this point steam pressure begins to show, which goes up very fast, as the water is all so near the steam temperature. Of course, it is better to carry the water at about the height shown, as a uniform pressure of steam is easier maintained, which is always desirable; yet the limit of safety is not reached till the water is nearly all out, or so long as it is not below the connection of the coils in the leg; and even at this point the only danger is in the damage to the coils from the heat when there is no water to protect them.

[Ill.u.s.tration: _VOL. II._ =STEAM FIRE ENGINE.= _PLATE x.x.xV._

Fig. 3390_a_.]

[Ill.u.s.tration: Fig. 3390.]

[Ill.u.s.tration: Fig. 3391.]

In Fig. 3391_a_, one engine and pump is shown in side elevation, and the other in section, the cranks being at a right angle, one to the other. A yoke from the piston rod spans the crank, so that the steam and pump pistons are in line and directly connected. From the lower end of this yoke, a rod connects to the crank shaft upon which are the two fly wheels and the eccentrics for the steam valves.

It will be seen in the longitudinal section, Fig. 3390_a_, that the steam valve face is a segment of a circle and therefore answers, so far as the distribution of the steam is concerned, to a simple D slide valve, which exhausts through the pipes _m_, _p_. The steam pipe _n_ enters the bottom of the steam chest at _n'_.

The two main pumps _a_ are made in one piece, entirely of composition; one of them is shown in section. The piston is a solid piece of bra.s.s, as well as the cylinder in which it works, but are made of different composition, one hard, the other soft, to prevent cutting. The valves are of India rubber; the discharge valve is a ring, one for each end of the pump, as shown at _b_, Fig. 3391_a_. One is shown open, while the other is closed. They are held in place by grooved rings of bra.s.s; these rings fit in grooves in the rubber, which, when they are put in the pump, and their set screws are in, with their points in the grooves in the bra.s.s rings spoken of above, the discharge valves are complete for work.

The suction valves are shown at K on Fig. 3391_a_, and will be easily understood. They are of a design for this special use and place, which is around the pump cylinder in a circular chamber. The water ways covered by these valves are long and narrow, one valve covering two of these openings, they being held in place by two studs that go through the centre part of the valve, a wire going through these studs, and close to the back of the valve which keeps it up to the seat, the only spring to either of these valves being the elasticity of the rubber. The opening and connection D, D is the inlet to the pump, and where the suction hose goes on, there being a pipe or chamber with branches for the two air chambers, and at each end is a discharge gate and a connection for the leading hose. The part _d_ is the feed pump for the boiler supply, _e_ is the air chamber on the pipe that leads to the boiler to ease off the shocks caused by the plunger striking the water, when the pump does not fill. It is drawn broken off to show the upper part of the pump barrel and stuffing box. The pipe _f_ is the feed water pipe from the pump to boiler, shown from different points in Figs.

3390_a_ and 3391_a_. _g_ is what we call the suction pipe to the feed pump. It connects to the main pump in the discharge part of it.

A piece of hose pipe connects to the boiler at a point just above the water line, so that hot water or steam (according to the height of the water in the boiler) may be applied to any part that may have become frozen.

[Ill.u.s.tration: Fig. 3391_a_.]

Heaters are almost universally used in connection with steam fire engines to keep the water hot, and in many cases to keep a few pounds pressure to shorten the time of going to work should the fire be close at hand. This boiler has an advantage for this kind of heating; the circulation is so perfect and free that all the water in it is heated alike; so when the fire is lighted the steam starts immediately up, instead of having to wait till some cold water has been heated that had not been reached by the very limited circulation in them, there being some parts that the circulation produced by the heater does not reach, leaving, of course, this water cold.

The arrows K" (Fig. 3391), show the direction of the circulation when working with fire in the fire box; those marked L" show the direction of it when on the heater which is directly opposite.

The outside pipe connected at about the water line is the outlet from the heater, and the inlet to the boiler, which carries the heated water over the crown sheet, where, as it gets cooler, it enters the coils, descends into the leg, and from there to the pipe near the bottom of the boiler; this pipe leads to the heater, so that the water is kept moving just in proportion to the heat given it; any kind of a heater can be used with the same result.

CHAPTER XLII.--MARINE ENGINES.

Marine engines are made in the following forms:

1. With a single or with two cylinders receiving live steam from the boilers, and exhausting into the atmosphere. These are termed high pressure engines, let the steam pressure be what it may. They are also, and more properly, termed non-condensing engines.

[Ill.u.s.tration: Fig. 3392.]

In the small sizes, such as are used for launch engines, it is simply a non-condensing engine, with a link motion for varying the point of cut off as well as for reversing purposes. Fig. 3392 represents an engine of this cla.s.s constructed by Chas. P. Willard & Co.

The cylinder is what is called "inverted," meaning that it is above the crank shaft.

The slide spindle or valve rod pa.s.ses through a guide and connects direct to the link block or die, as it is sometimes called.

The thrust block is provided in the bearing of the crank shaft, and consists, as seen in the sectional view, of a series of collars on the crank shaft bearing.

2. The addition to each high pressure cylinder of a low pressure cylinder const.i.tutes a compound engine, and if the engine has also a condenser, it is a compound condensing engine, an example being shown in Fig. 3392_a_, which represents an engine in which the link motions are employed to vary the points of cut off of both cylinders, as well as to reverse the engine. The engine being small, the power required to move the links is small enough to permit of their operation by hand, by means of the hand lever L, which is secured to its adjusted position on the sector T by the small lever nut shown on the side of the lever. The lever L operates a shaft D which shifts both link motions. The air and circulating pumps are at the back of the condenser, being operated from the beams B, B, each beam connecting to rods J which connect to rod _c_, which drives the air and circulating pumps.

The steam from the high pressure cylinder exhausts into a receiver or chamber between the two cylinders, and from which the low pressure cylinder receives its steam.

[Ill.u.s.tration: Fig. 3392_a_.]

[Ill.u.s.tration: Fig. 3395.]

[Ill.u.s.tration: Fig. 3396.]

The exhaust from the low pressure cylinder pa.s.ses into the condenser, where it is condensed, leaving a partial vacuum on the exhaust side of the low pressure piston.

Figs. 3393 and 3394 show the arrangement of the pumps on a pair of compound engines for a dredger. The steam from the low pressure cylinder pa.s.ses into the body of the condenser with which the air pump is in communication, as shown in the end elevation. At _a_ is the foot valve of the condenser. The piston of the air pump has a similar valve, and at _e_ is the delivery valve.

The circulating pump is shown in the back elevation (Fig. 3394), being a piston pump which forces the water through the tubes of the condenser.

There are two princ.i.p.al methods of compounding, in one of which the two cylinders are placed one above the other, with their axes in line, and both pistons connecting to the same crank, while in the other the cylinders are side by side, and each connects to its own crank, the two cranks usually being at a right angle.