PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 401 



that wlien the shaft is turned around, the valve has an cpycycloidal move- 

 ment over the valve face, opening and closing each port alternately in its 

 passage. This is a very beautiful movement, and permits the lead on each 

 piston to be adjusted to any required degree of nicety. The hollow M, in 

 the under side of the valve, is the exhaust passage. 



The packing of these pistons is a very simple point, and yet with all its 

 simplicity it is perfectly performed. We are assured that no leakage what- 

 ever is visible in the engine when at work. In figure 4, where the piston 

 is shown separately, the packing is also shown, and requires but little 

 explanation ; the mechanical reader can see that the steel bar N, fits in the 

 slot, 0, and is forced out by the spiral springs placed therein. There is 

 also a side plate, which is shown at P, in figure 2 ; this is forced inward 

 by wedges behind it, the wedges themselves being attached to a frame 

 which is worked by the set-screw, Q. This plate in connection with the 

 packing, R, makes the pistons perfectly steam-tight against the cylinder 

 cover, and yet easj^ working in all of their parts. 



In figures 4 and 5, the inner piston, or one on the crank-pin which is of 

 the same area, however, on its steam face as the external one, and the 

 crank shaft, are shown detached. The pistons waste little or no steam at 

 the completion of their stroke, as they work snugly up to each other, and 

 to the cylinder. There are no projecting bolt heads, and the steam ports 

 open directly on to the pistons, thus preventing the waste of steam which 

 occurs when long ports have to be filled with live steam at every stroke. 

 It is difficult to conceive of a more compact or efficient steam engine thaa 

 this in the same space. There are no " centers" or " dead-points" to the 

 crank, as each piston moves the crank alternately through one-half of its 

 circle, consequently there is never that mechanical loss which is expe- 

 rienced in ordinary single engines between the ti.nes of shutting off" the 

 steam during one stroke and opening the valve for another. In this engine, 

 we have alwa3'^s nearly an equal pressure upon the crank, depending, how- 

 ever, wholly upon the distance to which the live steam follows before it is 

 shut off". The speed of the piston in feet is not great as the stroke is so 

 short, but the engines run at an average rate of 150 revolutions per 

 minute. 



One of these engines is now working a pile-driver in this city. It raises 

 2,240 pounds (or one ton; 36 feet in 6 seconds ; taking 33,000 pounds raised 

 one foot in a minute as a standard-horse power, the engine in question 

 develops over 22 horse-power ; for 33,000 pounds raised one foot in one 

 minute are equal to 550 pounds raised one foot in a second ; and 2,200 

 pounds raised 36 feet in 6 seconds are equivalent to 360 pounds in one sec- 

 ond. One-fifth of 550=110 pounds, and three-fifths=330 pounds, or three- 

 fifths of a horse-power for every foot of distance. The whole distance 

 being 36 feet, it is easy to see that by this rule this engine has a power 

 exceeding 22 horses, minus friction. The pistons are 56 inches area by 5 

 inches stroke. 



The governor of this engine is peculiar, and constructed on proper prin- 

 ciples, as it is obvious that if the arms of the governor hang vertically 

 and are formed at right angles with each other, the movements are positive' 



[Am, Inst.] A* 



