STEAM ENGINE 



391 



of their places whilst the piston is being taken out, 

 or put into the cylinder, the periphery of it is 

 grooved near to its upper and lower edge, in which 

 are sunk two slight spring hoops, cleft across into 

 forked joints, which close together simply by their 

 elasticity. To lubricate the piston, there is a third 

 groove, made midway between the two former, for 

 the reception of oil ; these parts are not introduced 

 into the figures. The action is as follows : as the 

 piston and cylinder wear away by the friction, the 

 circular spring c, presses out the wedges b, and 

 these project the segments against the cylinder by 

 degrees as they are reduced in thickness. 



In the engine just described the cylinder is hori- 

 zontal, which is unusual, but the position of the 

 cylinder does not alter in any way the nature of 

 the principle upon which the steam puts the piston 

 in motion. 



It must be evident, that the steam escaping from 

 the cylinder of a high pressure engine, will be re- 

 sisted by the pressure of the atmosphere ; but if 

 the eduction pipe, in place of opening out to the 

 atmosphere, communicated with a vessel free of 

 air, and having a jet of cold water running into it, 

 so as to condense the steam as it entered, the steam 

 would then meet with no obstruction, in which 

 case, the steam from the boiler would act with 

 greater force on the piston. On this principle, as 

 we have already hinted at, is the condensing engine 

 constructed, which comes next to be described. 



We shall first notice the structure and action of 

 the condenser, together with the air pump, and 

 their connexions, as shown in the accompanying 

 cut. a a a a represents a section of the cistern, 

 containing cold water, b is the eduction pipe through 

 which the steam passes from the cylinder into the 

 condenser c. The condenser communicates with 

 the air pump e, by a pipe at the bottom, furnished 

 with a valve d, called the foot valve. This valve 

 is of the clack form. The air pump e, is of the 

 common suction kind, the piston being furnished 

 with two valves, as will be seen in the figure. 

 The valve g opens into the hot well h, and the 

 opening at h is the end of a pipe that allows the 

 surplus hot water in the well to run off, the re- 

 mainder being pumped into the boiler. At the side 

 of the condenser a rod is seen rising in the cistern, 

 the lower end being attached to an injection cock. 

 The water from the cistern passes through the in- 

 jection cock and enters the condenser through a 

 rose, in the form of a shower. 



Before the engine is set a going, the injection 

 cock being shut, steam is admitted into the cylin- 

 der, which, passing down through the pipe b into 

 the condenser, displaces the water and air contained 

 in the condenser, discharging them out through the 

 snifter valve n, which opens into the small chest . 



This operation of " blowing through," as it is termedt 

 being continued a sufficient time, and the cylinder 

 and condenser wholly filled with steam, the injec- 

 tion cock is then opened, and steam admitted to 

 the one end of the cylinder, while the other end 

 communicates with the condenser ; the injection 

 water immediately condenses the steam and the pis- 

 ton begins to move. The piston rod and air pump 

 rod being attached to the same end of the beam, rise 

 and fall together ; when the piston rises, the valve in 

 the bucket of the air pump will be shut, and all the 

 air and water above the bucket will be lifted through 

 the valve g into the hot well h. At the same time 

 a vacuum being formed in the air pump e, below 

 the bucket, more perfect than that in the condenser, 

 the foot valve d will be opened, and the water and 

 air will pass from the condenser into the air pump. 

 When the bucket descends, the valve in it will open, 

 and allow the air and water to pass into the space 

 above it, while the valves g and d will be shut. At 

 the return, the water and air is lifted through the 

 valve g to the hot well or cistern, as before, &c. 

 The condenser is usually made of the same capacity 

 as the air pump, each being equal to one eighth of 

 the content of the cylinder; that is, the length of 

 the air pump should be one half of the length of 

 the cylinder, and also its diameter one half that of 

 the cylinder. 



When a steam engine is made on this princi- 

 ple, the steam that is used has a low pressure, un- 

 less the engine be wrought expansively. (For an 

 account of which method of working an engine, see 

 the description of expansion valves given at the end 

 of this article.) 



Fig. 4, plate LXXXIII, is a view in section of 

 the steam cylinder and nozels of a condensing engine, 

 showing the piston with part of its rod, and the 

 steam valres with their rods and connections. 

 There are many different kinds of steam valves in 

 use; those shown are what are called D valves, 

 being different from those described for the high 

 pressure engine. The principle of them will be 

 best understood by referring to the cut fig. 3, page 

 388; and by supposing the pistons O O, to be 

 semicircular, with their flat sides next to the steam 

 ports, the face of the steam ports being also a flat 

 surface. We shall also suppose hemp packing to 

 be round the back of these pistons, or valves, for 

 the purpose of preventing the steam from passing 

 the valves, to the eduction side of the nozles, and 

 at the same time to keep the flat side of the valve 

 pressed to the other face c, the operation of the 

 steam passing to and from the cylinder, being the 

 same as was described when noticing cut, fig. 3. 



Fig. 1, 2 and 3, plate LXXXIII, are three views 

 of a twenty horse power condensing engine. First, 

 there are the nozles into which the steam enters 

 from the boiler, and from which the steam is ad- 

 mitted at proper intervals, into the cylinder, to 

 give motion to the piston ; the rods of it are seen 

 connected to the working beam by the straps or 

 links of the parallel motion. The other end of the 

 working-beam has the connecting rod attached to 

 it, which communicates motion from the beam to 

 the crank ; thus, with the aid of the fly wheel, pro- 

 ducing a rotatory motion to the crank shaft. The 

 vertical rods that hang down from the working 

 beam are for working the engine pumps ; the one 

 next the cylinder, is for the air pump ; that on 

 the other side of the main centre columns works 

 the cold water pump, which supplies the cold water 

 cistern with water for condensing the steam. It 



