A PNEUMATIC EXCAVATOR.

New Zealand Times, Volume XXXIV, Issue 5760, 15 September 1879, Page 3

A PNEUMATIC EXCAVATOR.

During the construction of the Tay bridge (says a London paper) considerable difficulty was experienced in sinking the cylinders for the piers, several expedients having been tried and abandoned. At length Mr. Reeves, one of the engineers engaged on that great work, succeeded in devising an excavator on the pneumatic principle, by means of which the sand was silked up from within the cylinders and discharged into the hoppers, the cylinders following down the displacement of the sand. One of these excavators, or sand pumps, as they are also called, has just been completed by Messrs. A. Wilson and Co., of the Vauxhall Iron Works, Wandsworth-road, and has been inspected at work on their premises by a number of engineers and other gentlemen interested in such matters during the present week. The excavator has been made for the New South Wales Government, and it is to be sent out to Sydney, where it will be used in sinking cylinders in connection with the improvements now in progress in the harbor there. The apparatus consists of a pair of cast iron cylinders 4ft. in diameter, carried on a staging and placed in connection at their tops with an air-pump, driven by a small steam engine. The connections are so arranged that the air can be exhausted either from one cylinder singly or from both at the same time. The bottoms of the cylinders are connected with a suction tube 3-Jin. in diameter, which leads down to the sand. Here again it is so arranged that the cylinders can be worked either singly or in combination by means of self-acting valves. The soil is discharged from each cylinder by a trap-door, placed in its front. The engine and air-pump are carried on the same framing, and the whole forms a very compact arrangement. In operation, the engine being started, the air is exhausted from one cylinder ; the sand and soil rushing up into the vacuum thus created soon fills the cylinder, the fact being indicated by a tell-tale. The connection is then made between the air-pump and the second cylinder, and that is similarly filled, during which time the contents of the first cylinder are discharged, and it is ready for the air-pump by the time the second cylinder is full, and so the process continues alternately until the desired end has been attained. The excavator worked very successfully ; a vacuum of 24 inches was maintained during exhaustion, and the cylinders were rapidly filled with sand and water from a pit, the contents being quickly discharged. Besides the Tay Bridge, this excavator has been advantageously used at the Dundee Esplanade, where a considerable quantity of land was reclaimed by its aid. It also succeeded in pumping the sand from a wreck at Fraserburgh, which led to the recovery of the vessel. In fact, the pneumatic excavator appears to have a wide field of practical application before it.