PRINCIPLES OF NAVAL ENGINEERING 



In 1698, Thomas Savery patented a condens- 

 ing steam engine which was designed to raise 

 water. This machine consisted of two displace- 

 ment chambers (or one, in some models), a 

 main boiler, a supplementary boiler, and ap- 

 propriate piping and valves. The operating 

 principles are simple, though most ingenious for 

 the time. When steam is admitted to one of the 

 displacement vessels, it displaces the water 

 and forces it upward through a check valve. 

 When the displacement vessel has been emptied 

 of water by this method, the supply of steam is 

 cut off. The steam already in the displacement 

 vessel is condensed as cold water is sprayed 

 on the outside surface of the vessel. The con- 

 densation of the steam creates a vacuum in the 

 displacement vessel, and the vacuum causes 

 more water to be drawn up through suction 

 piping and a check valve. When the displacement 

 vessel is again full of water, steam is again 

 admitted to the vessel and the cycle is repeated. 

 In a model with two displacement chambers, the 

 cycles are alternated so that one vessel is dis- 

 charging water upward while the other is being 

 filled with water drawn up through the suction 

 pipe. 



Although technological difficulties prevented 

 Savery's engine from being used as widely as 

 its inventor would have liked, it was success- 

 fully used for pumping water into buildings, for 

 filling fountains, and for other applications which 

 required a relatively low steam pressure. The 

 machine was originally designed as a device for 

 removing water from mines, and Savery was 

 convinced that it would be suitable for this 

 purpose. It was never widely used in mines, 

 however, because very high steam pressures 

 would have been required to lift the water the 

 required distance. The metalworking skills of 

 the time were simply not up to producing suitable 

 pressure vessels for containing steam at high 

 pressures. 2 



Although Savery's machine was used through- 

 out the 18th century and well into the 19th cen- 

 tury, two new steam engines had meanwhile 

 made their appearance. The first of these, 

 Newcomen's "atmospheric engine," represents 

 a real breakthrough in steam machinery. Like 



Savery's device, the Newcomen engine was 

 originally designed for removing water from 

 mines, and in this it was highly successful. 

 However, the significance of the Newcomen 

 engine goes far beyond mere pumping. The sec- 

 ond was the Watt engine, which brought the 

 reciprocating steam engine to the point where it 

 could be used as a prime mover on land and at 

 sea. 



The Newcomen engine was the first workable 

 steam engine to utilize the piston and cylinder. 

 As early as 1690, Denis Papin^ had suggested 

 a piston and cylinder arrangement for a steam 

 engine. The piston was to be raised by steam 

 pressure from steam generated in the bottom of 

 the cylinder. After the piston was raised, the 

 heat would be removed and condensation of 

 steam in the bottom of the cylinder would create 

 A vacuum. The downward stroke of the piston 

 would thus be caused by atmospheric pressure 

 acting on top of the piston. Papin's theory was 

 good but his engine turned out to be unworkable, 

 chiefly because he attempted to generate the 

 steam in the bottom of the cylinder. WhenPapin 

 heard of Savery's engine, he stopped working on 

 his own piston and cylinder device and devoted 

 himself to improving the Savery engine. 



The Newcomen engine, shown in figure 1-1, 

 was built by Thomas Newcomen and his assist- 

 ant, John Cawley, in the early part of the 18th 

 century.^ The Newcomen engine differs from 

 the engine suggested by Papin in several impor- 

 tant respects. Most important, perhaps, is the 

 fact that Newcomen separated the boiler from 

 the cylinder of the engine. 



As may be seen in figure 1-1, the boiler is 

 located directly under the cylinder. Steam is 

 admitted through a valve to the bottom of the 

 cylinder, forcing the piston up. The piston is 

 connected by a chain to the arch on one side of 

 a large, pivoted, working beam. The arch on the 

 other side of the beam is connected by a chain 

 to the rod of a vertical lift pump. 



^It is reported that Savery attempted to use steam 

 pressures as high as 8 or 10 atmospheres. When one 

 considers the weakness of his pressure vessels and 

 the total lack of safety values, it appears somewhat 

 remarkable that he survived. 



3papin is also credited with the invention of the safety 

 valve. 



4The year 1712 is frequently given as the date of the 

 Newcomen engine, and it is probably the year in which 

 the engine was first demonstrated to a large public. 

 It is likely, however, that previous versions of the 

 engine were. built at a considerably earlier date, and 

 some authorities give the year 1705 as the date of the 

 Newcomen engine. 



