^g BULLETIN 173, U. S. NATIONAL MUSEUM 



the driving and driven shafts turn in opposite directions, they turn 

 with the same relative positions so long as the intermediate gear re- 

 anains in one position. However, the axle of the intermediate gear 

 is pivoted about the driving shaft and is held in position only by the 

 governor rod, and the position of the intermediate gear changes with 

 «ach change of position of the governor rod. A change in position 

 of the intermediate gear advances or sets back the position of the 

 driven shaft relative to the driving shaft and varies the action of 

 the auxiliary steam valve relative to the action of the main-valve 



eccentric. 



RICHARDS BALANCED VALVE, 1866 



U.S.N.M, no. 308676 ; original patent model ; transferred from the United States 

 Patent Office; not illustrated. 



This model was submitted with the application for the patent issued 

 to Thomas Richards, of Lansingburg, N. Y., May 22, 1866, no. 54959. 



This model represents a slightly conical plug valve fitted within a 

 conical valve housing, which is provided with eight equally spaced 

 steam ports so arranged that diametrically opposite ports are con- 

 nected together in pairs. The result is that the pressure on the valve 

 due to the steam or exhaust pressure in each pair of ports is perfectly 

 balanced. 



Three adjoining ports in the valve housing are continued through 

 the housing, which is provided at that point with a flat surface that 

 permits the valve to be placed against the ordinary valve seat of a 

 D-slide valve engine, the three ports registering with the steam 

 passages to the ends of the cylinder and with the exhaust passage at 

 the center of the seat. The valve is constructed with four equally 

 spaced longitudinal recesses with four alternate bands. The valve 

 is operated by rocking it a part of a turn in each direction from the 

 center. 



The form of this valve and valve seat was patented by the inventor 

 February 23, 1858. 



BARTLETT POPPET VALVE GEAR, 1867 



U.S.N.M. no. 30S674 ; original patent model ; transferred from the United States 

 Patent Office; not illustrated. 



This model was submitted with the application for the patent issued 

 to Louis D. Bartlett, of Fitchburg, Mass., January 15, 1867, no. 61141. 



The patent refers to an engine with separate valve chests at 

 head end and crank end, each enclosing balanced steam and exhaust 

 poppet valves, and describes particularly tiie construction of the 

 valve boxes. These are designed for simplicity of casting, machining, 

 and accessibility but are difficult to describe without reference to the 

 drawings in the patent specifications. The valve gear used is said 



