Steam —A very considerable advance over the hand-engine is the steam fire-engine, which is a self-contained steam-pumping appara tus, the boiler, steam-cylinders, and pumping cylinders being carried in a frame to which is attached suitable running-gear. The smaller engines are drawn by men, the larger by horses. Self-propelling steam fire-engines have been constructed, but they have not been successful.
Figure 2 shows a " first-class " engine, weighing about 820o pounds and having a pumping capacity of eleven hundred gallons per min ute. A vertical boiler supplies steam to two vertical double-acting steam-cylinders, shown to the right of the boiler. The pistons of the steam-cylinders and those of the two pump-cylinders immediately below are on the same rods. The fly-whcel shown in the Figure serves to steady the motion. A suction air-chamber is shown below; the large air-chamber is to the left of the cylinders. The frame, known as " crane-neck," per mits the fore-axle to be turned at right angles to the length of the machine. This engine has steam-cylinders 93 inches diameter and 8-inch stroke; pump-cylinders inches diameter and S inches stroke. It will throw
from one to four streams, and will project a two-inch stream from 290 to 325 feet horizontally. The peculiar features in this type arc the boiler and the pump-valves. 'Pile boiler is of the vertical smoke-flue type, with pendent spiral water-tubes; it is shown more clearly in the section on Boilers (f/. 1). The pump has at each end a number of suction valves composed of rubber clappets opening inward, and near the centre two ring-shaped discharge-valves, opening outward; these valves have no springs to cause them to seat. The pump-heads are simply cages, and the piston is water-packed.
The Silsby steam fire-engine, shown in Figure 3 (pl. 117), has a boiler which, being shown more in detail on Plate 76 of the section on Boilers, needs no description here. The pump, which is of the rotary type, is driven by a rotary engine, and the axes of the pistons or "followers" of the engines are continuous with those of the pumps. A cross-section of the pump is shown on Plate rx5 x). The frame of this engine is "crane-necked," which facilitates turning corners. The axle is " cranked " or bent later ally around the boiler.