All About Engines

66 All About Engines those made by Galloway, Limited—the flues are only separate tubes at the furnace end. Beyond that they are united to form a single flue as shown in Fig. 32 on Plate 3. The oval form is not so strong as the circular, and the flue needs to be stiffened by a number of Galloway tubes ; but these increase the heating surface, improve the circulation, and raise the rate at which water is converted into steam. All sorts of devices have been tried to cause the hot water to move more rapidly over the heated surface, and more particularly to prevent the formation of quiet “ pockets ” of cooler water in any part of the boiler. Some of these consist essentially of guides to direct the stream of hot water as it rises in the immediate neighbourhood of the grate. Taken on the whole, the Lancashire boiler is a very good one for large factories and power stations. It may take five or six hours to raise steam from the cold ; but once the brickwork is hot it is econo- mical of fuel, and the large quantity of water it con- tains enables it to deal with a sudden demand for power. Moreover, the fires may be “ banked ” for a long time without the boiler and its setting be- coming cold. It is safe for low pressures, and is used often for producing steam at 200 lb. on the sq. inch. The “ Loco ” type of boiler shown in Fig. 33 is by no means restricted to use on railways, but is also employed for engines driving agricultural machinery, for traction engines, for road rollers, and for other purposes. The principal feature is the large number of tubes. In railway engines there