rOLYTECENIC ASSOCIATION PROCEEDINGS. ggT 



from the best engines which have preceded it, is the manner in 

 which the cut-oft' valves are operated, viz: by the action of the 

 steam itself, independent entirely of the action of the main valve; 

 thus insuring an instantaneous, positive, and easily controlled cut-oft* 

 at any desired point in the stroke of the piston. The distribution 

 of the steam to the alternate sides of the piston, and its release 

 from the cylinder when the stroke is completed, are performed in 

 the manner most approved by experienced engineers, by means of 

 a plane slide valve operated by the ordinary eccentric. But from 

 the fact that the induction valve has in no case to efiect the sup- 

 pression of the stream — or act as a cut-oft' valve — and from the 

 further fact that the cut-oft" is actuated independently of the motion 

 of the main valve, the functions of "lead" and "cushion" can be 

 adjusted to any desired degree, without in any manner aft'ecting 

 the action of the cut-oft" valve. This is an important distinction 

 between the operation of the main valve of this engine and those 

 which have preceded it. In the ordinary three-ported slide valve, 

 or in any other arrangement where the several functions of lead^ 

 cut-off, release, and comfpression, or closing the exhaust, are depend- 

 ent on the motion of one eccentric, the "exhaust" functions — i. e., 

 the release and compression — must always be subservient to the 

 "steam" functions — i. e., the lead and suppression, or cut-oft". 



In the Babcock & Wilson engine, however, the cut-off", being 

 actuated by a separate and entirely independent mechanism, a single 

 valve is capable of giving any degree of lead and compression 

 which may be desired, as perfectly as with the most complicated 

 valve gear. 



Another important difference between this engine and all pre- 

 vious adjustable slide or rolling valve cut-offs, lies in the fact that 

 the valves have a constant travel under all circumstances, thereby 

 insuring an equal wear. A valve which varies its throw to effect 

 the cut-off, as in all detachable valve gear, cannot wear equally, 

 and has a continual tendency to grow leaky. Again, this constant 

 throw insm-es a wide open port, and the least loss through throt- 

 tling the steam by the action of the valve — or, in other words, 

 enables us to obtain a pressure in the cylinder more nearly approach- 

 ing that in the boiler than can be realized with other valve motions. 



Another peculiarity of this engine is its extreme simplicity and 

 fewness of parts exposed to wear. At first sight, it has the appear- 

 ance of one of the simplest styles of non-expansive engines, having 

 none of the catches, cams, dash-pots, springs, tappets, etc., which 



