Cartwright's Engine

Courtesy of Denis McCormack, 404 W. Timonium Road, Timonium, Baltimore Co., Md. 21093 Cartwright's Engine (Cartwright's Engine. 1797.)

Denis McCormack

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Society of Automotive Engineers Courtesy of Denis McCormack

I am the fortunate possessor of an original copy of Elijah Galloway's 'History and Progress of the Steam Engine', published in London in 1831.

Written as it was by an engineer - himself an inventor of several early steam engine designs, at a time when the great development of the steam engine and its adoption to ships, railway locomotives, road vehicles and innumerable industrial applications was actually taking place, Galloway's book, despite its somewhat stilted English of 136 years ago, vibrates with the zeal and the excitement of an engineer partaking, observing and recording the great engineering developments of that period.

I would like to share the pleasure I have had in the reading and I shall be happy to furnish further extracts and illustrations that trace some of the fundamental forward moves which gave such great stimulation to modern progress.

Cartwriqht's Patented Steam Engine of 1797

'The Rev. Edward Cartwright's scheme for which he obtained a patent in 1797, was very ingenious. His object was to produce a tight piston, and a condenser in which the steam was exposed to a large surface of water.

The condensation is effected by two metal cylinders, placed one within the other, and having cold water flowing through the inner one, and inclosing the outer one. Thus the steam is exposed to the greatest possible surface in a thin sheet. Mr. Cartwright likewise has a valve in the piston by which a constant communication is kept up between the cylinder and condenser, on either side of the piston; so that any steam improperly entering the cylinder, is instantly exposed to the condenser, whether in the ascending or descending stroke. By this contrivance, steam that may escape past the piston will be immediately condensed, and the vacuum thereby preserved. This was considered to be a decided advantage over the general mode of arranging the valves, which does not always provide for the restoration of a vacuum destroyed by the imperfection of the packing.

In the following figure, the piston b moving in the cylinder a, has its rod prolonged downwards; another piston d is attached t o it, moving in the cylinder c, and which may be also considered as a prolongation of the steam cylinder. The steam cylinder is attached by the pipe g to the condenser, placed in cold water, formed of two concentric circular vessels, between which the steam is admitted in a thin sheet, and is condensed by coming in contact with the cold sides of the condensing vessel. The water of condensation falls into the pipe e. To the bottom of the cylinder i, a pipe m is carried into a box n, having a float ball o, which opens and shuts the valve p, communicating with the atmosphere: a pipe q is also fitted to the box. There is a valve placed at i, opening into the cylinder c; another at n, also opening upwards. The pipe s conveys steam from the boiler into the cylinder, which may be shut by the fall of the clack r. k is a valve made in the piston b.

In the figure, the piston b is shown as descending by the elasticity of the steam flowing from the boiler through s; the piston d, being attached to the same rod, is also descending. When the piston b reaches the bottom of the cylinder a, the tail or spindle of the valve k being pressed upwards, opens the valve, and forms a communication between the upper side of the piston and the condenser; at the same moment the valve r is pressed into its seat by the descent of the cross arm on the piston, which prevents the further admission of steam from the boiler; this allows the piston to be drawn up to the- top of the cylinder, by the momentum of the fly-wheel z, in a non-resisting medium. The piston d is also drawn up to the top of c, and the valve i is raised by the condensed water and air, which have accumulated in e, and in the condenser g. At the moment when the piston has reached the top of the cylinder, the valve k is pressed into its place by the pin or tail striking the cylinder cover; and at the same time the piston b striking the tail of the valve r, opens it; a communication is again established between the boiler and piston, and it is forced to the bottom as before. By the descent of the piston d, the water and air which were under it in the cylinder c, being prevented from returning into the condensing cylinder by the valve under i, are driven-up the pipe m, in the box n, and are conveyed into the boiler again through the pipe q. The air rises above the water in a, and when, by its accumulation, its pressure is increased it presses the float o downwards; this opens the valve p, and allows it to escape into the atmosphere.

This most ingenious machine, it appears, was tried first at Cleveland Street, Mary-le-bonne, and afterwards at Horsley down, at both of which places it is said to have given great satisfaction. These trials must have been much more decisive than any opinion; and although we have not been able to ascertain further respecting the success of the engines when put in practice, than the simple fact of their having been approved of by the respective proprietors, our own judgment warrants a conclusion, that this plan is admirably adapted to be applied where a small engine is necessary. The mode of condensation adopted by Mr. Cartwright was considered to be liable to great objection previously to experiment; so much so, that one of the greatest engineers this country ever produced, was heard to state it as his opinion, that 'were a pipe to be laid across the Thames, the condensation would not be quick enough to work a steam engine with its full effect.' It was shown, however, when tried, that this opinion was incorrect, as the condensation was very rapid, and the Vacuum tolerably good.

Not the least ingenious part of Mr. Cartwright's patent was the metallic piston, which has been of late years very generally used. Though this kind of piston is now somewhat differently modified from his, yet he is entitled to the merit of having first introduced it into use. It has been found to answer extremely well, and frequently works for years without needing any attention, and merely requiring to be kept well greased.

Mr. Cartwright's consists of two rings of brass, of the full size of the cylinder, which are cut into segments, as shown at 111, and laid one above the other so as to break joint. The joints, therefore, in the under ring are shown by dotted lines in the figure? and being thus disposed, the two rings are secured in their places by a top and bottom plate, to which the piston rod is fixed. The segments are pushed against the cylinder by steel springs, shown at n n.'