FIRE ENGINE. This most useful machine is constructed in a variety of forms, which all, however, agree in ono principle. It generally consists of a dou ble forcing pump communicating with the same air vessel ; and instead of a force-pipe a flexible leathern hose is used, through which the water is driven by the pressure of the condensed air in the air vessel. The an nexed diagram repre sents a section of the apparatus. The pipe T descends into a re ceiver or vessel con taining a supply of water. This pipe communicates with two suction valves V, which open into the pump barrels' of two forcing pumps A, 13, in which solid pis tons r, are placed. The piston rods of these are connected with a working beam F, elongated so that a number of persons may work at both ends of it at once. Force-pump barrel above the valves V, and pipes t, t, proceed from the sides of the they communicate with an air vessel M, by means of forcing valves V, which also open upwards. The pipe descends into the air vessel near the bottom. This pipe is connected with the flexible leath ern hose L, the length of which is adapt ed to the purposes to which the machine is to be applied. The extremity of the hose may be carried in any direction, and may be introduced through the doors and windows of buildings. By the alter nate action of the pistons, water is drawn through the suction valve, and propelled through the forcing valves, until the air in the top of the vessel M is highly com pressed. The pressure acts on the sur face of the water in the vessel, and forces it through the leathern hose in a con tinued stream, so as to spout from its extremity with a force depending partly on the degree of condensation, and partly on the elevation of the extremity of the hose above the level of the engine. It is to be considered that the pressure of the condensed air has, in the first in stance, to support a column of water, the height of which is equal to the level of the end of the tube above the level of the water in the air vessel ; and until the pressure exceeds what is necessary for this purpose, no water can spout from the end of the hose ; and, consequently, the force with which it will so spout will be proportional to the excess of the pres sure of the condensed air above the weight of the column of water, whose height is equal to the elevation of the end of the hose above the level of the water in the air vessel.
A steam lire-engine has been built by Mr. Braithwaite, of London, for the King of Prussia. It is intended to be exclu sively employed for the protection of the public buildings of Berlin.
The combustion is promoted by means of an exhauster, instead of a bellows ; the flue is in two lengths, and the greatest diameter 5 inches. The steam-cylinder is 12 inches in diameter, with a 14 inch stroke. The water cylinders are 101 inch. in diameter, with also a 14 inch stroke. The steam from the eduction-pipe is con veyed through two coils of tubing laid in the water tank, and imparts a consider able degree of heat to the water before it .
is transferred to the boiler. The feed pump is equal to the supply of from 20 to 25 cubic feet of water per hour.
The steam is got up (in 20 minutes.) and the pressure in the boiler is at 70 the square inch. The height to which the water is ejected is not less than from 115 to 120 feet. The number of strokes per minute is 18, which gives for the quantity of water thrown 1 ton 7 cwt. 13 lbs. per minute.
The water cylinder being 104 in dia meter, the area of the water piston must be 86.6 square inches ; And a 14-inch stroke of the engine gives for the length of the stroke in the water cylinder 56 inches ; Therefore, 86.6 X 56 = 4849'6 cubic inches of water each stroke = 2.8 cub. ft. Deduct for back-water through the valves 1 cub. ft., leaves for the effectual result 2.7 cub. ft.
And, multiplying 2.7 by 1.8, the num ber of strokes per minute, we have 4843 cubic feet per minute = 3037 lb.s =1 ton 7 cwt. 18 lbs.