Y6 BULLETIN 173, U. S. NATIONAL MUSEUM 



to one end of its individual walking beam, from the other end of 

 which a connecting rod connects to a crank on a crankshaft carry- 

 ing a large flywheel common to the two cylinders. From either side 

 of the center of each beam a connecting rod goes to the piston rod of 

 one of the four pump cylinders. A condenser pump is also operated 

 from one of the two walking beams. The valve gears are operated 

 by eccentrics on the shaft, through a series of bell cranks and rods,, 

 and ball governors driven by belts from the shaft control the cutting- 

 off of steam to the cylinders through rods extending to the tripping 

 mechanism on the cylinder steam valves. Each cylinder, valve gear, 

 governor, and walking beam is a separate and complete unit. The- 

 beam, flywheel, and operating cylinders are located below the level 

 of the steam cylinders in a well formed of heavy masonry, which 

 also forms the foundation of the engine. The model is operated by 

 a hand crank. 



CORLISS VACUUM DASH POT, 1875 



U.S.N. M. no. 308692; original patent model; transferred from the United States- 

 Patent OflSce; not illustrated. 



The model was filed October 27, 1875, with the application for the 

 patent issued to George H. Corliss, June 6, 1876, no. 178275. 



The model is a brass miniature of a vacuum dash pot designed to 

 combine the functions of supplying the force to close the steam valve 

 and to arrest the motion without shock after the valve is closed. 

 The vacuum dash pot has some advantages over heavy weights and 

 springs for closing valves. 



The dash pot consists of a casting in which is bored a cylinder 

 having a lower section of small diameter and an upper section of 

 larger diameter. A plunger, having corresponding sections of large 

 and small diameters, fits the cylinder. When the steam valve to 

 which the plunger is attached is opened the plunger rises in the cyl- 

 inder forming a vacuum in the part of smaller diameter. At the 

 same time small leather valves in the larger part of the plunger open 

 and allow air to enter the cylinder under this part of the plunger^ 

 When the valve is released the vacuum draws down the plunger and 

 closes the valve. The air under the upper part escapes through a 

 port in the cylinder until the plunger covers the port.. The air 

 trapped in the cylinder at this point acts as a cushion and brings 

 the valve quickly but gently to rest. 



CORLISS STEAM PUMP FOR WATER AND AIR, 1876 AND 1877 



U.S.N.M. no. 308694; original patent model; transferred from the United States 

 Patent Office ; not illustrated. 



This model represents two patents issued to George H. Corliss, of 

 Providence, R. I., December 19, 1876, and May 22, 1877, nos. 185390 

 and 190958. 



