430 



THE STEAM-ENGINE. 



valves by which steam from the boiler may be admitted and withdrawn. These 

 steam-boxes are connected by a tube of communication T, and they communi- 

 cate with the cylinder at the top and bottom by short tubes represented in the 

 figure. The upper steam-box A contains one valve, by which a communication 

 with the boiler may be opened or closed at pleasure. The lower valve-box 

 contains two valves. The lower valve I communicates with the tube T 7 ,' lead- 

 ing to the condenser D, which being opened or closed, a communication is 

 made or cut off at pleasure, between the cylinder C and the condenser D. A 

 second valve, or upper valve H, which is represented closed in the figure, may 

 be opened so as to make a free communication between the cylinder C and the 

 tube T, and by that means between the cylinder C, below the piston, and the 

 space above the piston. The condenser D is submerged in a cistern of cold 

 water. At the side there enters it a tube, E, governed by a cock, which, being 

 opened or closed to any required extent, a jet of cold water may be allowed to 

 play in the condenser, and may be regulated or stopped at pleasure. This jet, 

 when playing, throws the water upward in the condenser toward the mouth of 

 the tube T', as water issues from the nose of a watering-pot. The tube S pro- 

 ceeds from the boiler, and terminates in the steam-box A, so that the steam 

 supplied from the boiler constantly fills that box. The valve G is governed by 

 levers, whose pivots are attached to the framing of the engine, and is opened 

 or closed at pleasure, by raising or lowering the lever G 7 . The valve G, when 

 open, will therefore allow steam to pass from the boiler through the short tube 

 to the top of the piston, and this steam will also fill the tube T. If the lower 

 valve H be closed, its circulation beyond that point will be stopped ; but if the 

 valve H be open, the valve 1 being closed, then the steam will circulate equally 

 in the cylinder, above and below the piston. If the valve I be open, then steam 

 will rush through the tube T 7 into the condenser ; but this escape of the steam 

 will be stopped, if the valve I be closed. The valve H is worked by the lever 

 H', and the valve I by the lever I'. 



The valve G is called the upper steam-valve, H the lower steam-valve, I the 

 exhausting valve, and E the condensing valve. 



From the bottom of the condenser D proceeds a tube leading to the air-pump, 

 which is also submerged in the cistern of cold water. In this tube is a valve 

 M, which opens outward from the condenser toward the air-pump. In the pis- 

 ton of the air-pump N, is a valve which opens upward. The piston-rod Q of 

 the air-pump is attached to a beam of wood called a plug-frame, which is con- 

 nected with the working-beam by a flexible chain playing on the small arch- 

 head immediately over the air-pump. From the top of the air-pump barrel 

 above the piston proceeds a pipe or passage leading to a small cistern B called 

 the hot-well. The pipe which leads to this well is supplied with a valve, K, 

 which opens outward from the air-pump barrel toward the well. From the 

 nature of its construction, the valve M admits the flow of water from the con- 

 denser toward the air-pump, but prevents its return ; and, in like manner, the 

 valve K admits the flow of water from the upper part of the air-pump barrel 

 into the hot-well B, but obstructs its return. 



Let us now consider how these valves should be worked in order to move 

 the piston upward and downward with the necessary force. It is, in the first 

 place, necessary that all the air which fills the cylinder, the tubes, and the con- 

 denser, shall be expelled. To accomplish this, it is only necessary to open at 

 once the three valves, G, H, and I. The steam then rushing from the boiler 

 through the steam-pipe S, and the open valve G will pass into the cylinder 

 above the piston, will fill the tube T, pass through the lower steam-valve H, 

 will fill the cylinder C below the piston, and will pass through the open valve 

 I into the condenser. If the valve E be closed so that no jet shall play in the 



