Transactions of the Institute of Mining and Mechanical Engineers, Vol. XXXII, 1882-3, pp.55-7
At the general Meeting which was held on the 14th of October, after the reading of M. C. Tylden-Wright's paper on the "Channel Tunnel," it will be remembered that Sir Edward 1Vatkin invited the members of the Institute to visit the Tunnel Works at Dover. Subsequent correspondence with Sir Edward fixed the 18th of November as the day for the visit, and circulars were issued to all the members inviting them to attend. About 110 members expressed their desire to avail themselves of Sir Edward's kindness, and, at his request, a list of these gentlemen was for warded to him. Sir Edward then took the matter into his own hands, and, with his usual liberality, supplied each gentleman with a free pass from his place of residence to Dover and back.
The party assembled on the platform of the Charing Cross Station of the South-Eastern Railway at nine o'clock in the morning of the 18th, and were received by Sir Edward Watkin, the Chairman, and Mr. Shaw, the General Manager of the Railway, and conveyed in the special train which had been provided for them to Dover. The party descended the shaft in batches of thirty, and were taken to the face of the Tunnel in carriages pushed by hand. Many, however, walked- along the Tunnel with a view of more particularly examining the details of the work which had been executed.
The 'funnel was lighted by electricity, on the incandescent principle, and as a general description of the Tunnel has been given in Mr. C. Tylden-Wright's paper, it would be useless here to recapitulate the particulars.
The surface machinery is of the ordinary kind for compressing air, and does not seem to require any detailed description. The little coin pressed air locomotive, however, which was described in detail by Colonel Beaumont, elicited general admiration and was under the most complete control. It is built of a suitable size to go into the Tunnel, and was running about on a railway on the surface, laid on a curve and gradient of 1 in 80, corresponding to the heaviest duty it will have to do in removing the debris under ground. It consists of a reservoir, or air receiver, about 9 feet long and 3 feet 6 inches in diameter, with circular ends, welded up into one solid piece containing Go cubic feet. The working pressure is from 1,000 lbs. down to 100 lbs. per square inch, and the reservoirs were proved by Messrs. Daniel Adamson & Co., the mad:erg,-1,o 1,500 lbs. per square inch; under this pressure they are absolutely without alteration of form. It is proposed to renew this test every year, and, at the same time, to wash out the interior of the reservoir with boiled oil to prevent any corrosion taking place. A large margin of safety is allowed, and at the same time it is impossible that the working pressure can exceed 1,000 lbs. A small quantity of water accumulates in the reservoirs during the working of the machinery and is let out occasionally- by means of a small cock at the bottom. The air is conveyed from these vessels to two compound engines, working at right angles to each other, each having cylinders respectively of 2 inches and 7 inches diameter, and the valve gear, which forms a special feature, is so arranged that the air can be cut off ill the small cylinder tit any point from zero to full stroke. Under special circumstances, such its starting with a heavy load, the air call be admitted direct to the large cylinder.
One of the most interesting and important portions of Colonel Beaumont's invention is the use of a small boiler, not much larger than an ordinary hat, which receives its heat from a few handfuls of coke. The steam from this boiler jackets both the cylinders, and also heats the air before it reaches them. Working under normal conditions of load the heat so obtained enables the air to be expanded from 1,000 lbs. downwards without inconvenience, so that the whole, or a very large proportion of the whole, theoretical pressure due from this expansion is utilised, the air coming out at a temperature of from 80 deg. to 90 deg. causing no difficulty with the exhaust to be experienced.
The length of this engine is about 13 feet, its width over all 3 feet 6 inches, and its height from road level 5 feet.
The principle on which the engine is constructed may be summed up as one enabling high pressures to be used without the loss entailed by a reducing valve, and at the same time keeping the temperature of the air from dropping during expansion, without mixing air and steam together.
During the visit the Company supplied air to a couple of fixed reservoirs, whence it was taken, by adding a flexible hose, to the engine; the operation of filling, including coupling, did not exceed a couple of minutes.
It is this arrangement which allows high pressure to be used with economy.
One cubic foot of air, at sixty-eight atmospheres, is produced from a consumption of one pound of coal, and it will haul a gross load of three tons (including the engine) one mile on the level portion of tin ordinary well laid railway, a ton and a half on an ordinarily constructed tramway, and three-quarters of it ton on such lines and with such rolling stock as would be used in a colliery.
Colonel Beaumont stated that with large compressors and improved machinery the duty would probably be increased some 50 per cent. The machine under inspection had been very hurriedly built for the Channel Tunnel; but the engine Colonel Beaumont was introducing for mining purposes, while producing the same results, was very materially simplified.
For the information of those who were waiting to go below, a number of experiments were made with Smith's lime cartridges, and lame masses of chalk were brought down the side of the cliff. Professor Abel's dynamite shell, in which the dynamite is encased in it water cartridge, was also exhibited. A little before two o'clock the party left by special train for Dover, where they were entertained by Sir Edward Watkin at the "Lord Warden" Hotel, and returned to London by a special train arriving at about six o'clock