CHAP, in.] PUMPS. 61 



The best steam fire-engines of all descriptions are those in which 

 the force-pumps are direct acting, the steam- and water-pistons being 

 connected by rigid rods, without the intervention of any joint, so that 

 the force communicated by the steam to the steam-piston is instan- 

 taneously transmitted to the water-piston without any shock or blow. 



We give in this place a drawing of one of the most powerful 

 steam fire-engines known Shand and Mason's Equilibrium fire 

 engine. The special arrangements of the pumps will be seen from 

 the accompanying woodcut. For these engines it is important that 

 steam should be got up at once. In the " equilibrium " engine, by 

 means of a special arrangement of boiler, to which we shall refer 

 hereafter, steam of 100 Ib. pressure can be got up in 6J minutes. 

 Great economy of steam, and consequently of boiler space and fuel, 

 is thus obtained, and the weight of the whole machine is greatly 

 reduced. 



The engine will throw a jet through a l^-inch nozzle 130 feet 

 high, throwing in 1 7| minutes nearly 7,000 gallons of water. 



The equilibrium steam fire-engine is fitted with a set of treble 

 pumps, worked directly by a corresponding treble set of steam- 

 cylinders, by the use of which a perfect uniformity is obtained in 

 the flow of water through the hose- and suction-pipes, avoiding all 

 shocks to the engine or pipes, and producing jets quite as steady as 

 those obtained by pressure from gravitation. The use of the three 

 steam-cylinders, besides securing the above advantages, enables the 

 fly-wheel to be dispensed with, but the crank and rotary motion is 

 retained, as all other substitutes have failed in securing a fixed length 

 of stroke of piston. 



In the horizontal fire-engine the arrangements are somewhat dif- 

 ferent. They will be understood from the accompanying section, p. 62. 



c, a slotted cross-head formed by the ends of the piston-rods of 

 steam- and water-cylinders, and containing the sliding bearings 

 of the crank D, to which it communicates a rotary motion ; L, the 

 auxiliary cylinder, with its piston M, fixeH on A, the slide-valve rod ; 

 H, the slide-valve of the main cylinder, the frame of which moves the 

 slide-valve K of the auxiliary cylinder ; N, a ratchet lever to enable 

 the engine to be moved round by hand. 



B 1 , the valve-box cover of the water-cylinder, which, when removed, 

 allows the four India-rubber valves with their seats and guards to be 



