84 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Maucu, 



the Blackwall end of tlie line, but also for maintaining a suitable 

 dcffiee of tension on tlio ])art of tlic rope behind the train, wliilst 

 it is in motion. The object of keepin^^ the tension on tlie rope is 

 to |)rc\ent it from beinp unwound from off the drum faster than the 

 train proceeds, and to secure the ro]ie against tlie risk of breakaj,'e, to 

 which it would be liable, if it were allowed to become slack and 

 then to he suddenly ti^rbtcned, by the acceleration which takes 

 place in the motion of the train, after it has commenced the 

 descent of a steeper gradient than that on which it was previously 

 travelling. 



The engines beinp: only worked for eight or nine minutes out 

 of every ijuarter of an hour, the vacuum in the condenser might 

 during the remaining si.\ or seven minutes become ini])erfect from 

 leakage, or from air contained in the injection water ; in which 

 case the restarting of the engines would be difficult, except by pre- 

 viously blowing steam through the condenser, to displace the air, — 

 for the greatest power is re([uired at starting, when the machinery, 

 be drums, the rope, and the train, have all to be set in motion 

 from a state of rest, and tlieie must be a good vacuum in the con- 

 denser to enable tlie engines to start promptly. For this object an 

 engine of 12 horse-power is provided, and constantly works two 

 auxiliary air-iiumjis, wliich maintain the vacuum in the condensers 

 of the large engines, independently of the action of their own 

 air-pumps. 



In the arches upon which the railway is carried to pass over the 

 engine-house, eiglit mttfr-tnnks are placed, all connected together 

 by pipes. The overilow of waste water from the hot cisterns of 

 the engines, is conducted from the usual overflow-pipe into the 

 most distant of the eight tanks. From that tank the water passes 

 into the next, and tlien to the next, and so on to the last of the 

 eight tanks, in which it is mixed \vith fresh cold water, and the 

 mingled water is then conveyed into the engine-room, for supply- 

 ing the injection cocks of the engines. The surface of the water 

 in the eight tanks is exposed to the atmosphere, and the hot water 

 thus becomes cooled in passing through them. At first there were 

 only three tanks, in which, as they exposed a large surface to the 

 air, it was expected the cooling of the water would proceed with 

 sufficient rapidity to render it fit for injection upon arriving at the 

 third tank, and being there mixed with fresh cold water ; but, as 

 it was found tliat there was not a sufficient cooling effect, five more 

 tanks were added, and the eight tanks novv in use are scarcely suf- 

 ficient for cooling the water to the extent required. The supply of 

 cold water, for mixing with the water in the tanks, is pumped by 

 the 12 horse-power engine from a well in the adjoining part of the 

 building, and, in addition to this supply, a small pipe is laid on 

 from the main of the New River Company. The temperature of 

 the injection water in summer is about 80°, and often higher, and 

 the vacuum then obtained is about 21 inches of mercury ; in winter 

 there is no difficulty as to the temperature of the vvater, and the 

 mercury stands at from 27 inches to 28 inches. Each of the tanks 

 is 21.^ feet square and G feet deep, so that the capacity is 3,600 

 cubic feet, and the surface of water exposed is 600 square feet in 

 each tank. 



The steam-pipe from the boilers passes through the wall, and is 

 carried inside the engine-room to the right and left to each pair of 

 engines, with a valve-box, from which two branches proceed to 

 supply each engine. The valve in the box is opened and shut by a 

 screw, worked from below by a handle, by which the engineman 

 regulates the speed of the engines. 



The governor is placed beyond the outer frame of the pair of 

 engines, and the number of its revolutions is to the number of 

 strokes made by the engines as 3 to 2. It is worked from the 

 crank of the engines by a pair of bevil wheels on a small axis 

 passing through the outer frame. The governor acts upon a 

 throttle-valve placed in the steam-pipe, immediately beyond the 

 shut-off valve. The resistance the engines have to overcome 

 varies so much, that the governor was found not to be capable by 

 itself of regulating the speed, and therefore it was assisted by the 

 man dosing the shut-off valve by its screw handle; but latterly 

 the governor has lieen disconnected, and is not now used. 



T" avoid snatching the rope, by which it might be broken, great 

 care is taken to start the engines as gradually as possible, in order 

 that all the slack of the rope may he gathered up around the drum, 

 and then the train he started slowly, and gradually accelerated to 

 the full speed. The valve is therefore only partially opened at 

 first, and is afterwards opened fully by degrees ; as the engines 

 acquire speed, the valve is closed again gi-adually, to restrain the 

 speed, as the carriages arri\e one after another, and the resistance 

 diminishes. 



The Bviti-rs. — The boiler-house is beneath the railway, the five 

 boilers being placed under the arches on which the continuation of 



the railway is carried beyond the engines. Two of them are 

 square marine-boilers, with the ordinary internal furnaces and 

 rectangular dues ; the other three boilers are constructed on the 

 Cornisli system, being (urciiUr, with two internal tubes through 

 their entire length, and the furn»<-es in the front ends. The two 

 marine-boilers, which are equal in power to the three Cornish 

 boilers, are ca]>able of sup])lying steam for one jiair of engines. 

 The two marine-boilers, or the three Cornish boilers, are worked 

 together as a set, the two sets being used alternately in the same 

 manner as the engines, but for about three months at a time. 

 The chimney is situated between the two sets of boilers. The 

 flue from each separate boiler, enters into a main flue, which ex- 

 tends along the back of each set to the base of the chimney ; 

 each is provided with a separate damper, and there is another 

 damper at the end of each main flue, where it joins to the base of 

 the chimney. 



On tlie top of the steam-chest of each boiler is a shut-off valve 

 box, joined by a branch to the main steam-pipe, which leads to the 

 engines. By these valves, any boiler may be shut ofl' from the rest, 

 in case it is required to be cleaned whilst the others are at work. 

 At the mid-length of the steam-)ii])e are two safety-valve boxes, 

 each having an aperture of 12 inches diameter ; they com- 

 municate with each other, and from one of them a discharge-jiipe 

 proceeds into the chimney ; one of these safety-valves is out of 

 the control of the men, but the other may be lifted by means of a 

 lever worked from below, in order to discharge the steam at the 

 end of the day's work. 



The feeding of the boilers is efl^ected from a tank situated above 

 the arches, at the side of the chimney, at such a height as to give 

 the column of water entering the boiler a greater pressure tiian 

 that of the steam. This feeding-tank is 10 feet in diameter, bv 6 

 feet high, and is capable of holding 471 cubic feet of water. 'I'he 

 water is raised into this tank by the pumps of the engines, and 

 feed-pipes proceed from the tank to the feed-cocks in the pipes, 

 at the front of the several boilers. During the time the engines 

 are at work, no water is admitted to the boilers, but as soon as 

 they are stopped, the feed-cocks are opened, and the water is al- 

 lowed to flow in until the proper level is restored. At the same 

 time a fresh supply of coals is thrown on the fires, to raise the 

 steam for starting. This is so managed as to waste very little 

 steam by blowing away at the safety-valve. 



The diimnri/ is 6 feet square inside, at the base, and 4 ft. 3 in. 

 diameter at the top, and 161 feet high from the foundation. The 

 draught is exceedingly good. The sjtaces opposite to the row of 

 furnaces of the five boilers are stores for coal. Beneath the centre 

 of the passage, in front of the row of furnaces, is the drain for 

 carrying off the waste water. 



The steam-enguiet) o( 112 horse-power (nominal power) are on 

 the marine construction, with side levers, the same as Messrs. 

 Maudslay, Suns, and Field made for steam-vessels a few years ago. 

 That construction was adopted, as it was requisite that the centre 

 of the shaft should be elevated. Tlie diameter of the cylinders 

 is 56 inches ; the length of stroke is 5 feet ; and the average 

 number of strokes 22 per minute. The motion of the piston is 

 therefore 220 feet per minute. The plunger feed-pump is 6A 

 inches diameter, and 2 ft. C in. stroke ; only one pump is workea 

 at a time. The cranks are all of cast-iron, with axes of wrought- 

 iron, 12 inches diameter in the bearings. 



The /uriie xpur-wheet on the main axis is 1 7 feet in diameter at 

 the pitch line, with 120 teeth ; the pitch of the teeth is 5j inches, 

 and their breadth is 23 inches. The centre boss of this wheel 

 consists of two circular pieces bolted together externally, including 

 between them, and closing over the roots of the arms, which are 

 eight in number, cast separately, and bolted to one another, and 

 to the boss. The rim is in eight segments, each having 15 teeth, 

 and the junctions of the segments are made at the ends of the 

 arms. The weight of the wheel is 16,j tons ; that of the rim by 

 itself being 8 tons 13 cwt. The drum is 23 feet in diameter out- 

 side, and 10;L feet in diameter at the bottom of jtbe V-shaped 

 groove, wherein the rope is coiled. The w idth of this part, at the 

 bottom, is 1 ft. 6 in., and at the top 3ft. 2 in.; when all the 

 rope is wound on it, the diameter of the outside coil of the rope 

 is 20 feet. 



The limak-wheel at the side of the drum is 14 feet in diameter, 

 and 1 foot broad. 



The nmrticc sptir-whcc/, on the axis of the drum, and at the same 

 side as the break, is 11 feet in diameter at the pitcli line : it has 

 78 cogs, which are also 23 inches bi'oad. 



Although the drum, the break-wheel, and the mortice-wheel, 

 have hitherto been mentioned as separate, they are in fact all 

 framed together so as to form one coaihination. The tot;J weight 



