balls are used, although the centrifugal force developed by revolving weights is utilized to regulate the speed.

This engine represents the type which is fitted with a shaft governor that changes the eccentricity of the eccentric to perform the cut-off.

Fig. 8 shows the Buckeye governor which utilizes the centrifugal force of revolving weights, and the tension of coil springs to regulate the speed as in the preceding case, but the throw of the eccentric is not changed. When the eccentric on a slide-valve engine is set to give the required lead the valve cuts off at a given point in the stroke according to the design of the valve. If the eccentric is rolled farther forward the cut-off will be shortened, but the valve travel will remain the same.

FIG. 7

SCIENCE AND INDUSTRY.

The Buckeye governor operates on this principle, as it rolls the eccentric on the shaft, moving it forward for a shorter cut-off and backward for a longer cut-off, according to the load on the engine.

Fig. 9 is a diagram from one of these engines, showing variations in the load.

The foregoing diagrams from engines fitted with shaft governors, show the same compression for various loads. This is due to the fact that the cut-off valve does not control the compression, therefore changing its position does not affect the time for closing the exhaust port on the return stroke.

There is, however, a large class of engines fitted with shaft governors, which have only one valve, conse

quently it controls the compression as its position is changed to meet the requirements of varying loads. This This affects the regulation of speed as will be shown later on.

The Armington & Sims engine belongs to this class, and its governor is illustrated in Fig. 10. It stands in this position when the engine is first started, then as the speed is increased the weights 1, 1 are thrown outward by centrifugal force, the effect of which is to roll the inner eccentric in one direction, and the outer one the opposite way. By this means the eccentricity is reduced, the travel of the valve is

the advance of the piston, the compression is immediately decreased, which reduces the resistance from back pressure.

an engine is running with a light load. which is suddenly increased, the time required for the speed to be adjusted to the new conditions is equal to the

Fic. 13

SCIENCE AND INDUSTRY.

load the compression is light, but as soon as some of this load is thrown off and the engine inclines to run faster in consequence, the governor shortens the point of cut-off, and at the same time increases the compression, and consequently the resistance from this cause, so that the speed is kept very nearly constant under great changes in the load.

Much has been said and written concerning the necessity of providing uniform speed for electric-light engines, which is proper, but the need of good regulation for engines that are driving machinery in mills and factories does not receive the same attention, because the bad effects of varying speed with this class of machinery are not so plain to the observer as they are when he is looking at an electric light.

cut-off and get a larger volume of steam into the cylinder. Suppose that it requires 6 revolutions to accomplish this, then in the case of an engine revolving 90 times per minute, it will take 4 seconds, but where 300 revolutions are made in the same time it calls for only 1 seconds. The whole of this difference may not be realized in practice, but the chances for the highspeed engine to adjust itself to the new conditions in the shorter time are much better.

On the other hand, if we assume that

FIG. 14

SCIENCE AND INDUSTRY.

FIG. 15

age when regulation under changes of load are considered, because it makes more revolutions in a given time. If

it is in direct proportion to the difference in revolutions required.

While the time required for adjustment to new conditions is an important factor, it is of much less consequence than to have the adjustment properly made for economical work. For illustration suppose that the difference in speed between a light and a heavy load is 2 per cent. in one case and 5 per cent. in another. In all shops and factories, whether the work is done by the piece or day, the output is regu

lated by the speed of the engine. As the machines are belted so as to run at various speeds according to their several requirements, if the speed of the engine is reduced 5 per cent., the output of the works is reduced in the same proportion, and this applies to the other case where the reduction was 2 per cent. As the difference between these engines is 3 per cent., it follows that the output of the factory having the best regulated engine is 3 per cent. greater than the other, although the expense of running is nearly as great for one speed as another in some cases, and in others it is fully as much.

If we compare two mills, or factories making the same goods, with everything else equal, this difference

The high-speed engine possesses a natural advantage in this respect, but the improvements made in governors for low-speed engines, brings them into close competition with their more favored rivals, as a fly-ball governor can be made to run much faster than the crank-shaft which drives it, thus taking advantage to a certain extent of the benefits of a high speed for this service.

It will be noted that this article does not discuss the merits of the high-speed engine except in regard to regulation.

ONSIDERING the fact that water

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tube boilers are being extensively used each year, it may be of interest to note a few of the accidents that happen to them most often. The use of these boilers is at the present time confined almost exclusively to the marine service," excepting the large tube boilers such as those of the Babcock & Wilcox type, which are practically in a class by themselves.

The following tube accident occurred to a small tube boiler, and a similar accident is liable to happen to any boiler of this type. It occurred on the trial trip of a torpedo boat in April, 1901, but fortunately no lives were lost.

DESCRIPTION OF THE BOILER.

Thorny-croft water tube "Speedy type." Grate surface, 45.6 square feet. Heating surface, 2,516 square feet. Capacity, 1,000 H. P. at 4' water pressure. Steam drum, 30" inside diameter, thick, 10 ft. long.

Water drums, 16 inside diameter, thick, 9' 3" long.

h

Down take pipes, 7 inside diameter, thick.

Tubes, rows A and B, 140—11′′ diameter, inside No. 11 B. W. G. Rows C to L, 776-1" diameter, inside No. 11 B. W. G. Total water in boiler to working level 8", 4,370 lb.

Total water in boiler above point of explosion, 1,100 lb.

Total fuel in grate in state of combustion, 4,000 lb.

Rate of combustion at time of explosion was 95 lb. of coal per square foot of grate surface.

Kind of coal used: Picked Pocahontas. Fig. 1 shows an end view and section lengthwise through the boiler.

During the full-speed run of the boat, when everything was working smoothly, a rush of flame came out at the top of the smokestack, mounting to a height of about 20 feet, and lasting fully five seconds. The heat was intense, the stack immediately, becoming red hot. The fire-extinguisher spraying jets, located in the arch of the furnace immediately over the fires, were opened at once, spraying 50 gallons of water

per minute on the burning coal; the automatic stop-valves were closed, shutting off communication with the other boilers, and the boat proceeded to her destination under two boilers.

The pressure at the time of the accident was 265 pounds per square inch, the limit allowed for her working pressure.

As a result of the accident the steam drum was found to have sagged two inches at the back, buckling the after angle iron bracing and destroying the

tubes in this immediate vicinity were injured. Fig. 2 shows the exploded tube and Fig. 3 the burned tube. The steam drum and tubes were found covered with a thin coating of red oxide of iron, the appearance being the same as that of iron after it is heated to a cherry red and allowed to gradually cool in a moist atmosphere. These indications were mostly on the upper port side. It is to be noted that aside from the one tube blown out in "B" row and the destruction of aline

tube alinement, and the tubes on both sides of the boiler were found to be out of alinement. One tube in "B" row, port side, indicated in Fig. 1, was exploded, opening out toward the fire. About 35 tubes were pitted and blistered. The location of these tubes being shown by the dotted section in Fig. 1. A noticeable fact is that one tube in row "K" near the back was burned through at the point where it entered the wing drum, while no other

ment, the walls next the fire were not otherwise damaged; also, that on the starboard side no marks of burning were detected. To discover the extent of the damage about 250 tubes were removed from the boiler and only 35. were found to be injured by blistering.

It is to be understood that these boilers and tubes were thoroughly tested and had steamed nearly 500 miles without the slightest indication of trouble-this being one of nine