PRINCIPLES OF NAVAL ENGINEERING 



or so after the Newcomen engine was opera- 

 tional. However, Watt's brilliant and original 

 contributions were ultimately responsible for 

 the utilization of steam engines in a wide variety 

 of applications beyond the simple pumping of 

 water. 



In 1799 Watt was granted a patent for certain 

 improvements to "fire-engines" (Newcomen 

 engines). Since some of these improvements 

 represent major contributions to steam engi- 

 neering, it may be of interest to see how Watt 

 himself described the improvements in a speci- 

 fication: 



"My method of lessening the consumption of 

 steam, and consequently fuel, in fire-engines, 

 consists of the following principles:— 



" First , That vessel in which the powers of 

 steam are to be employed to work the engine, 

 which is called the cylinder in common fire- 

 engines, and which I call the steam vessel, 

 must, during the whole time the engine is at 

 work, be kept as hot as the steam that enters 

 it; first by inclosing it in a case of wood, or 

 any other materials that transmit heat slowly; 

 secondly, by surrounding it with steam or other 

 heated bodies; and thirdly, by suffering neither 

 water nor any other substance colder than the 

 steam to enter or touch it during that time. 



" Secondly , In engines that are to be worked 

 wholly or partially by condensation of steam, 

 the steam is to be condensed in vessels distinct 

 from the steam-vessels or cylinders, although 

 occasionally communicating with them; these 

 vessels I call condensers; and, whilst the en- 

 gines are working, these condensers ought at 

 least to be kept as cold as the air in the neigh- 

 bourhood of the engines, by application of water 

 or other cold bodies. 



" Thirdly , Whatever air or other elastic 

 vapour is not condensed by the cold of the con- 

 denser, and may impede the working of the 

 engine, is to be drawn out of the steam-vessels 

 or condensers by means of pumps, wrought by 

 the engines themselves or otherwise. 



" Fourthly , I intend in many cases to employ 

 the expansive force of steam to press on the 

 pistons, or whatever may be used instead of 

 them, in the same manner in which the pressure 

 of the atmosphere is now employed in common 

 fire-engines. In cases where cold water cannot 

 be had in plenty, the engines may be wrought by 



this force of steam only, by discharging the 

 steam into the air after it has done its office." 



As a result of these and other improvements, 

 the Watt engine achieved an efficiency (in terms 

 of fuel consumption) which was twice that of the 

 Newcomen engine at its best. Among the other 

 major contributions made by Watt, the following 

 were particularly significant in the development 

 of the steam engine: 



1. The development of devices for translat- 

 ing reciprocating motion into rotary motion. 

 Although Watt was not the first to devise such 

 arrangements, he was the first to apply them 

 to the task of making a steam engine drive a 

 revolving shaft. This Ofie improvement alone 

 opened the way for the application of steam 

 engines to many uses other than the pumping of 

 water; in particular, it paved the way for the 

 use of steam engines as propulsive devices. 



2. The use of a double-acting piston— that 

 is, one which is moved first in one direction 

 and then in the opposite direction, as steam is 

 admitted first to one end of the cylinder and then 

 to the other. 



3. The development of parallel-motion link- 

 ages to keep a piston rod vertical as the beam 

 moved in an arc. 



4. The use of a centrifugal "flyball" gov- 

 ernor to control the speed of the steam engine. 

 Although the centrifugal governor had been used 

 before. Watt brought to it the completely new— 

 and very significant— concept of feedback. In 

 previous use, the centrifugal governor had been 

 capable of making a machine automatic; by add- 

 ing the feedback principle. Watt made his ma- 

 chines self-regulating.6 



Neither Newcomen nor Watt were able to 

 utilize the advantages of high pressure steam, 

 largely because a copper pot was about the best 

 that could be done in the way of a boiler. The 

 first high pressure steam engines were built by 



The distinction between automatic machines and 

 self-regulating machines is of considerable signifi- 

 cance. An automatic pump, for example, can operate 

 without a human attendant but it cannot change its mode 

 of operation to fit changing requirements. A self- 

 regulating pump, on the other hand, operates auto- 

 matically and can change its speed (or some other 

 characteristic) to meet increased or decreased de- 

 mands for the fluid being pumped. To be self-regulat- 

 ing, a machine must have some type of feedback 

 information from the output side of the machine to 

 the operating mechanism. 



