CATALOG OF THE MECHANICAL COLLECTIONS Ql 



a quick, sharp cut-off that could be varied without interference with 

 the other valve events. At first it was designed only for hand ad- 

 justment of the detaching device. In 1849 George H. Corliss patented 

 the first valve gear in which the drop cut-off was combined with 

 and controlled by the engine governor (see below). This inven- 

 tion with its subsequent refinements was very widely adopted by 

 engine builders throughout the world and has very substantially 

 affected the design of steam engines down to the present time. It 

 has been said of the Corliss valve gear that "no other device has 

 given greater prestige to American engineering." 



The Corliss inventions and engines represented in the Museum 

 collection are grouped together at the end of this title. 



SICKELS DROP CUT-OFF VALVE GEAR, 1841 



U.S.N.M. no. 308650 ; original patent model ; transferred from the United States 

 Patent Office ; not illustrated. 



This model was part of the application for the patent issued to 

 Frederick E. Sickels, of New York, N. Y., May 20, 1842, no. 2631. 



The Sickels valve gear is generally considered to be the first suc- 

 cessful and practical drop cut-off. It was widely used on the engines 

 of the side- wheel steamboats up to the beginning of the present cen- 

 tury and was the forerunner of the many subsequent designs of drop 

 cut-off valve gears. This valve gear provides a means of rapidly 

 cutting off the admission of steam to the cylinder of the engine at 

 any point in the stroke of the piston. It accomplishes this by tripping 

 or disengaging the valve from the valve gear and permitting it to 

 drop to its seat under the impulse of a spring. A plunger operating 

 in a water chamber gradually retards the falling valve and brings 

 it to rest without shock. 



The Sickels valve is of the conical or poppet type, working vertically 

 with the valve stem directed upward. Motion is transmitted to the 

 valve through a lift rod working up and down continuously parallel 

 to the valve stem. Spring clips on the lift rod engage with the pro- 

 jections on the valve stem and lift and open the valve, until the clips 

 come into contact with wedge-shaped blocks, which spread the clips 

 and permit the valve to fall back to its closed position. The wedge- 

 shaped disengaging block can be placed so as to cause the valve to dis- 

 engage and close at any desired instant during the up or down move- 

 ment of the lift rod. A spring bearing upon the top of the valve 

 stem causes it to close rapidly, while a plunger or piston attached 

 to the under side of the valve and working in a chamber of water 

 retards the valve gradually and permits it to close without shock. 

 The lift rod may be actuated by an eccentric or, as was more usually 

 the case, by cam and follower of the "alligator jaw" or steamboat 

 type of gear. 



