be changed into the stronger cylindrical form, and thus the real strength of the boiler would be increased.

Experience leads to the opinion, that the safety-valves and the steam-pipe orifices are the two most dangerous parts of any boiler; and that explosions are much more likely to occur at these parts, or directly opposite to them, than at any other part. This opinion is based upon the fact, that several locomotive boilers have burst at those parts, arising, it is believed, from the concentrated rush of steam to the steam-pipe, or to the safety-valve, as either might be opened, and to the internal equilibrium in a weak boiler, becoming thus destroyed.

This would produce a local pressure, for an instant, far greater than the ordinary pressure, and if the point of collision, or its opposite point of reaction, failed to resist that pressure, rupture would ensue, even though the safety-valve should be in perfect order, and should not be overloaded. The vast elastic force, of the expanding water and steam, thus suddenly released, would, like any other spring, exert a force far beyond the limit due to the quiescent pressure, and after investigation might show, that the explosions had frequently resulted from tampering with the safety-valves. It may also be noticed, that the ordinary safetyvalve does not open its entire area to any boiler, but only a concentric ring of about one-eighth, or one-fourth of an inch wide, which is too little for such expansive force, even when directed against the valve itself. Suppose, for example, that the pressure in a boiler is 100 lbs. per square inch, in a quiescent state, but that the sudden opening of the regulator, or safety-valve destroys that equilibrium; there is then an instantaneous rush of steam towards that opening, and a simultaneous formation of steam by the disturbed water; therefore, it is not the 100 lbs. pressure which the boiler has to sustain, but it is the collision of various forces of 100 lbs. each, sustained by the rapid formation of more steam, which the boiler has to resist, and which leaves their destructive energies only too apparent, when rupture ensues.

This view of the explosive force of steam and heated water, does not involve any supposed tampering with, or neglect of valves, so often mooted, and it is believed to be more in accordance with the known powers of elastic force and boiler resistance.

Before closing these remarks, it is desirable also to call atten

tion to the numerous cases of passenger-engines, or trains running off the rails, without apparent cause, although goods', or slow trains seldom meet with the same casualty.

This points directly to velocity as the ruling cause, and to deeper wheel-flanges as a simple and good remedy. It is quite probable, that many of these accidents might have been prevented, by a flange only one-half inch deeper than the present one; for, at the high velocities now run, a flange of one inch deep, is but a narrow limit between safety and danger. An extension to 1 inch, or even 2 inches, where the rails would admit of it, would greatly increase the safety, without, in the slightest degree, increasing the friction in running.

When the late Mr. Stephenson designed the Liverpool and Manchester Railway, and speeds of only fifteen miles, or twenty miles an hour were contemplated, flanges about one inch deep were sufficient, as is still proved by goods' and other slow trains. But now that heavy engines and high speeds of fifty miles and sixty miles an hour, over indifferent roads, are in the ascendant, a greater depth of flange is required, alike for public safety and railway economy.

From what has been stated, it may be concluded

That different boilers at different speeds, or the same boiler at different velocities, are not economically comparable.

That fuels differ nearly as much in their steaming powers as boilers.

That a cubic foot of water, as steam, gives out a power varying with the temperature of that steam.

That boilers, with pressures varying from 90, 100, 110, to 150 lbs. per square-inch, are not tractively comparable.

That evaporative economy is not confined to any one form of boiler, and is influenced by the fuel used.

That economy of evaporation may be purchased at the cost of speed and power.

That the economic length of tubes, in ordinary boilers, depends upon the velocity of running and the temperature of the

steam.

That Mr. McConnell's boiler gives great constructive facilities, for further improvements in locomotive boilers.

That the Great Western, and other boilers on high wheels, combine the elements of evaporating power and economy.

That boiler explosions are frequently due to internal commotion acting against some local point.

That deeper wheel-flanges would increase the public safety.

The discussion upon the Paper, No. 887, "Experimental Investigation of the Principles of the Boilers of Locomotive Engines," by Mr. D. K. CLARK, being resumed, was continued throughout the evening.

April 12, 1853.

JAMES MEADOWS RENDEL, President,

in the Chair.

No. 888." On the Concussion of Pump Valves." BY WILLIAM GEORGE ARMSTRONG, M. Inst. C. E.

In constructing force pumps, for working hydraulic cranes, and other machines of a similar nature, under a high pressure, considerable difficulty has been encountered, in arriving at a form of valve free from injurious beat, or concussion; and as, after many experiments, the object appears to be attained, it may not be uninstructive to describe the proceedings.

The head of water, against which the pumps were required to act, in the particular instance alluded to, was equivalent to a column of 1,200 feet, and was obtained, artificially, by means of an accumulator, or loaded press, which served, in every respect, as a substitute for a reservoir of that elevation. These force pumps were fixed at cach end of the cylinder, and the plungers worked in a direct line with the piston of a high-pressure engine, with a horizontal cylinder and regulating fly wheel.

Fig. 1.

In designing the pump valves, the Author proceeded upon the generally received opinion, which is, that concussion is caused by the fall of the valve upon its seat, and with that view, in order to afford the necessary passage for the water, with an extremely small rise, the valves were made of an annular form, to allow the water to escape on all sides; and very large, in proportion to the size of the plunger.

A spiral spring was also applied, to press upon each valve, to insure its closing promptly, at the termination of each stroke; and a screw adjustment was used, to vary the pressure of the spring.

The form and construction of this valve are exhibited by Fig. 1, and the general

form of the pump by Fig. 2, the latter being slightly varied from the reality, for the sake of clearer illustration.

Fig. 2.

In order that the water might flow into the pumps independently of suction, the cistern for feeding them was placed at a considerable elevation. It was calculated, that, with the pressure given by the spring, the greatest rise of the valve would not exceed one-twentieth of an inch, and as this rise would gradually diminish, as the plunger travelled from the middle towards the end of the stroke, it seemed difficult to conceive, that any concussive effect could attend the final closing of the valve.

Upon trying the pumps, however, when fitted with these valves, a violent shock was found to take place, once during each stroke of the plunger; and as this shock was identical, in point of time, with the fall of the suction valve, it was assumed, that the defect was in that valve, and not in the delivery valve. When