and the distance from center to center of knuckle joints is 12 inches. The 

 rod has a sohd head (no other joint) and a case hardened box, with a 

 single key and set screw. The valve is moved by a yoke, in which the rod 

 is fastened by nuts. The yoke does not in this case prevent the evil it is 

 usually designed to avert, — the stripping of valve stems. 



The length of the ports is the great charm of Niles & Go's, engines. The 

 port for 15 and 16 inch cylinders is i x 18 inches. If 18 square inches of 

 port area astonishes the fearful, they will at least acknowledge that length, 

 and not width, is the important dimensions of a given port. If an opening 

 contains 1 2 square inches, and is 8 inches long and i }^ inches wide, when 

 the valve cuts ofT at say 9 inches, and opens half an inch, the total opening 

 will be 4 sq. inches. But if the same area is spread out into 12 inches 

 long by I inch wide, a valve opening of ](, inch will give a total opening of 

 6 sq. inches, when cutting oflF at 9 inches. Now if an engine running at 

 40 miles an hour so wire draws her steam that a cylinder pressure of 60 

 lbs. is attained out of a boiler pressure of 100, with a 6 inch opening 

 what will the cylinder pressure be with a 4 inch opening? Diagrams tell 

 a story about narrow ports, that has not been generally understood. 



Again, with a short port, a greater lap and lead are required to produce 

 the same effect on the piston. The ports we have described with a % 

 inch lap, will do as well as the ordinary port with an inch lap. But what is 

 the objection to inch lap? A long valve, a large cup in the valve, a great 

 pressure over the cup to consume power and wear out machinery, is one 

 objection. There are others which we shall consider at another time. 



Two words more, however, will tell us how we can have the boiler 

 pressure in the cylinder, and light machinery, and preserved power; — 

 BALANCED VALVES. 



The slides of the Niles machines are held up after one of the Norris 

 styles. A thimble is placed between the back ends of each of the rods, 

 and a brace from the side of the barrel, forming a fl at the bottom rests 

 on their top, a bolt passing through the thimble and fl on each pair. 

 Each rock-shaft has two boxes, one on the slide and one on the frame, the 

 valve arm being between the two. Suppose the slides to get out of line 

 by wear or accident, is the box on the slide to be refitted? There is longer 

 leverage, however, and less twist and wear in the boxes, with this arrange- 

 ment. 



The pump has the ordinary flat valve, is not ugly to look at, and is said 

 to work well. Speaking of pumps, any decent pump will work well enough, 

 if the valves do not raise too high, or leak. The check valve is simple 

 and well arranged. Some builders make a very expensive edifice on the 

 side of the barrel, just to take in water. This is a mere elbow pipe, with 

 a valve seat secured at the bottom with two bolts, and a thread cut on it 

 to receive the hose coupling. 



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