P2

Assuming, then, P2 = 15 lbs. per sq. inch, and p1 equal successively to higher pressures up to 140 lbs. per square inch, we can calculate the number of lbs. q of steam flowing into the atmosphere for the various values p1 of boiler pressures, and by means of the table we may turn the pounds into cubic feet. The latter values multiplied by 144 give the velocities of outflow in feet per second. The following diagram shows the result of such a calculation:

It will be seen that for all boiler pressures above 25 lbs. absolute the velocity of issuing steam is above 800 feet per second. Now, if the periphery of a turbine one foot in diameter is to have this speed, the number of revolutions per minute must be at least 15,000, and such a turbine ought to have about the same economy as an engine with no expansion.

A couple of simple calculations of the centrifugal force in such a wheel may be of interest.

First. Suppose a wheel one foot in diameter to have projections around its circumference, like teeth in a spur gear. Let each projection or tooth be a cube of one inch on each side, so that the metal contained in it is a cubic inch, and the section which must give way when it flies off is one square inch. Suppose the weight of the cubic inch to be a quarter of a pound, then the centrifugal force of each tooth is, roughly,

so that the material would need to have a tensile strength of over 12,500 lbs. per square inch for such a wheel to run 15,000 per minute without the teeth flying off by centrifugal force, and for a speed of 30,000 the tensile strength would need to be four times as great.

Second. Suppose instead of the teeth a ring of metal were put around the wheel, the cross section of the ring being one square inch. The centrifugal force for each cubic inch of the ring would be the same as before, 12,500 lbs., which would be the same as an internal bursting pressure of 12,500 lbs. per square inch. Multiplying this by the radius, six inches, there results 75,000 lbs. for a rough value of the tensile strength per square inch of a ring capable of withstanding the centrifugal force of 15,000 revolutions per minute.

The effect of centrifugal force will also appear in the enlargement of the diameters of the parts when running, which will require suitable allowances to be made for such enlargement. Such allowances can easily be calculated for special forms of rotating parts.

CCCXLVI.

THE DISTRIBUTION OF STEAM IN THE STRONG LOCOMOTIVE.

(Supplementary Paper.)

BY F. W. DEAN, CAMBRIDGEPORT, MASS.

(Member of the Society.)

A YEAR ago I had the honor of reading a paper upon this subject,* and therein called attention to the anomaly that the cylinder performance of the engine No. 444 was inferior to that of No. 383, and but little better than that of engine No..357, the latter being the link-motion and D-valve engine. The average consumption of steam by the diagrams was as follows:

The only plausible explanation of the difference that could be given was, that it was due to the leaking of the steel valves of No. 444, which were known to be wearing badly. In June, 1888, castiron valves were placed in the engine, and in the August following the writer took a number of indicator diagrams, copies of some of which are herewith presented (Figs. 154 to 160), with the object of seeing if any change in steam consumption had taken place. The following is the average result:

Engine No. 444, in August, 1888

21.95 lbs.,

or slightly better than the results from No. 383. The horse powers given are the totals for both cylinders.

The claim which the writer made, that the initial pressure of the steam in the cylinder of the Strong engine is only some 3 lbs. below the boiler pressure, was consistently verified, as the diagrams show.

Since preparing that paper the writer has experimented upon a

* Trans. A. S. M. E. Vol. IX, p. 556 ch. CCCIV.

more recent Strong locomotive in competition with a link-motion engine, and has been pleased to see that his claims concerning the capacity of the Strong cylinder to perform work was fully borne out in the most practical manner. The runs were over a division of one of our leading trunk lines from New York westward, the distance being 140 miles, and the actual schedule time westward being 3 hours 27 minutes, and eastward 3 hours 46 minutes, after deducting time for stops. This gives the average speed westward 40.6 miles per hour, and eastward 37.14 for times in motion.

The two engines had cylinders and driving wheels identically the same, and the average boiler steam pressures were nearly alike. The usual point of cut-off for the Strong engine, when hauling a heavy train, was 6 inches, and for a light train 4 inches, while the points for the link-motion engine were, for similar conditions, respectively 11 inches and 8 inches, and in nearly every case the Strong engine made up the most time, and drew the heaviest trains.

The points of cut-off were accurately determined, and the trains consisted of from six to twelve cars. The link-motion engine is one of the finest modern engines to be found in the country, and was in first-class order. The valves of both engines were proved to be tight.