There may be no practical difficulty in constructing a large circular wooden vat or water-tank, but there cannot be any great actual economy, except in those countries where suitable timber is very cheap, and iron very dear. The wooden tank must be made of selected materials, and by skilled workmen; but however carefully constructed it cannot be expected to last so long as an iron tank. In many parts of the United States of America there are excellent examples of the circular wooden tank, strongly put together, and covered with a light ornamental roof. Numbers of these wooden tanks have been erected there in places where the cost of carriage alone of an iron tank would have been a serious item, and where suitable timber was fortunately 302 close at hand. In cases where engines are watered direct from a water-tank, a simple delivery-valve, as shown in the sketch (Fig. 458), will answer the purpose. This valve has to be pulled open by the chain and lever, D, and when released falls with its own weight, and is kept closed by the pressure of the water above. The delivery-pipe should not be less than 7 or 8 inches in diameter, to accelerate the filling of the tenders. Where water has to be delivered to engines at two or more places in a station-yard, and the supply derived from the same principal tank, the result may be obtained either by laying down 7 or 8-inch main pipes from the principal tank to separate water-columns, or by erecting two or more pedestal water-tanks, similar to Figs. 459 to 462, each of which holds a little more than the average quantity for one tender, and can be fed from the principal tank by a comparatively small pipe of 3 or 4 inches in diameter. It is simply a question of expense--whether it is cheaper to lay down a long length of 7 or 8-inch main pipe and ordinary water-columns, or to adopt the small pipes and pedestal tanks. Figs. 459 to 462 are sketches of a medium-sized pedestal water-tank to hold 1200 gallons. The supporting column must have a very wide base, bolted down to a solid foundation. The tank itself, made circular in plan, is generally constructed of light plates of wrought-iron or steel, the lower portion or floor of tank being very securely attached to the vertical column. Notwithstanding their top-heavy appearance, these pedestal tanks can be made very firm and steady if enough width be given to the base-plate, and the tank properly fixed to the column. Water is led into these pedestal tanks by a small pipe passing up inside the supporting column, and the delivery may be effected by a simple valve, as explained for Fig. 458.