50 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[February, 



No. 2. 



4 



4 



4 



4 



4 



4 



4 



4 



4 



4 



4 



4 



4 



3-75 



3-52 



3-34 



3-1/ 



3- 



6-78 



46-23 



Carry this again further out, by admitting the steam only dining ^ 

 = i of the stroke, and we shall find for the expenditure of steam 5x4 = 

 20, and the sum of the forces for the first five spaces will be 5 x 4 = 20, 

 and for the remaining 15 it will be 26-2S. 



The consumption of steam in this case will be 20 = 1. 



The power exerted will be 20 + 26-28 = 46-28 = 2-31. 



(See diagram No. 3.) 



To obtain the greatest possible advantage from steam it is requisite : 

 1st. To employ it expansively. 



2nd. To admit it into the cylinder at its full pressure without being wire- 

 drawn. 

 3rd. That the portion of the stroke during which it is admitted freely, 

 should be determined by the engine governor. 



The construction of this self-acting slide expansion valve, will be under- 

 stood by inspection of Figs. 1,2: 



A, being the face of the cylinder. 



H, the slide valve, acting exactly the same as the ordinary slide valve. 



Ii a moveable metallic plate, worked by friction against the back of the 

 slide valve H, as far each way as will be permitted by the cam or tappet a, 

 the position of which will be determined by the governor. 



When the points of the tappets are approached so as to hold the plate I, 

 the sUde valve H, alone will move, and the steam will act only during a very 

 small portion of the stroke of the piston. 



When the points of the tappets separate, the plate I, will be carried along 

 with the valve, until brought in contact with the tappets, and the greater the 

 distance between the points of the tappets, the longer the steam will be ad- 

 mitted into the cylinder. 



When the tappets are sufficiently thrown back to prevent the plate I, from 

 reaching them during the whole length of the stroke of the valve, the fixed 

 bracket K, will then place the plate I in the middle of the slide valve, and 

 the steam will be admitted during the whole length of stroke of the piston, 

 with the exception of what portion may be cut off by the advance of the 

 eccentric. 



The two spindles which carry the tappets a, pass through stuffing boxes 

 reserved on one side of the valve box, and are turned by two sectors fixed 



on their extreme ends, and working into each other ; the tappets therefore 

 move simultaneously in contrary directions, a lever fixed to the top sector 

 being worked by the governor, so as to separate the points of the tappets a, 

 as the speed of the engine diminishes, and to approach them nearer toge- 

 ther as the speed increases, and in this way steam will be admitted in such 

 volumes into the cylinder, as will effectually regulate the speed of the engine 

 without ever contracting the orifice of the throttle valve. 



This summary explanation is quite sufficient to show the principle upon 

 which this valve is constructed, and by what means the purpose is effected ; 

 what follows, is a somewhat more detailed account of the same, useful only 

 as entering a little more minutely upon the subject, and giving some in- 

 structions to be attended to in its construction. 



To facilitate the setting of the metallic plate I, attention must be paid to 

 the position of the tappets a, because upon their position depends the 

 proper effect of the valve. The upper sector G, is keyed on the end of the 

 spindle, and the lever F, is fixed to the sector by two screws b, running 

 through oval holes in the sector, which permit the spindle to be turned a 

 little either way, so as to move the points of the upper tappets a little nearer 

 to, or a little further from the plate I. 



On the lower spindle the same facility is obtained, by keying a plate on 

 the spindle, instead of fixing the sector itself, and then by fixing the sector 

 to the plate by two screws, giving play in the holes as above, the bottom 

 tappets can also be varied as may be required. 



To cause the plate 1 to adhere to and follow the vale H, in its motion, a 

 l spring K, is fixed on the back of the plate I, and the two ends of the spriug 

 slide in a groove, formed by two side pieces fixed to the slide valve ; this 

 spring is so disposed as to press the plate against the back of the valve. 



I have occasionally applied this valve to engines that required to have 

 more steam thrown on to one side of the piston than on the other, and have 

 thereby been able to do away with a considerable counterweight — for in- 

 stance, in direct engines, where there is considerably more weight in the 

 down than in the up stroke, I have found it very useful ; and in another 

 case, in which a cold water pump was attached to one end of the beam, and 

 lifted water from a very deep well. 



The motion of the valve being determined by an eccentric, is exactly the 



