168 



THE CIVIL ENGIXEEIl AND ARCHITECT'S JOURNAL. 



[Jink, 



FRICTION CURVE 



A well-known defect in revcilvina: valves is their want of tight- 

 ness after some use, or tlieir great friction when tightened by force. 

 In a stop-cock with a conic:il i)lug, for instance, the amount of 

 wear in the bigger ])art differs from that in the smaller part, be- 

 cause every point in the former has a longer way for friction than 

 any point in the latter. To lessen this defect^ it is necessary to 

 make the plug nearly cylindrical. The consequences thereof are — 



1. A comi)arativeIy trifling pressure causes the plug to stick in 

 its socket like a wedge. 



2. The bore, instead of being made round, as it ought to be for 

 giving tlie fluid a free passage, must be made flat. 



3. \ ery little wear causes the plug to sink considerably in its 

 socket; from which again results 



4. The necessity of making cocks comparatively long and heavy. 



Fig. 1. Fig. -2. 



Fig. 6. 



Fig. 6. 



The friction between a plug and its socket divides itself so that 

 the products of the pressure multiplied with the length of way are 

 the same for any point in tlie rubbing surfaces. The length of 

 way being difi"erent in different parts, the jiressure must differ also : 

 it is greatest on the smaller end. Now, as tlie bigger end must be 

 tight as well as any otlier part, the destructive wear [abrasion] of 

 smaller parts is apparent. Therefore, considering such a trun- 

 cated cone to be dix ided into infinitely narrow ones, I propose to 

 take a more obtuse cone for each bigger part; and in such progres- 

 sion, that it would require equal pressure for every point in the 

 surface to cause an uniform, sinking of the plug in its socket by 

 wear The shape thus obtained is one with a curved surface, as 

 shown in fig. 1. 



The main feature of the generating curve for such a siirface is 

 the equality of all tangents drawn to the axis. Hence tlie use of 

 an instrument I constructed as shown in tig. 2, A, ami B, where the 

 curve is described by a little drawing-pen moving on a liorizontal 

 plane. 



Figs. 3 to 6 show some examples for the application of the de- 

 scribed principle. 



Fig. 3.- A. 



Fig. 3.— B. 



Fig. 3, A and B, represent two stop-cocks, which from their 

 shape may be called ie/?-cocks. They have none of the imperfec- 

 tions of those now in use, while they possess the natural tendency 

 of insuring tightness by wear. 



Fig. 4 represents part of a regulator for a locomotive engine, for 

 transmitting the angular motion from the handle to the inside of 

 a boiler; here the amount of friction varies with the pressure of 

 steam which acts against the journal. 



Fig. 5 represents an axle for astronomical or surveying instru- 

 ments, &c. ad, bb, cc, are annular parts of one 

 and the same curve surface, and are so chosen 

 merely for the purpose of exemplifying the va- 

 riety of ways in which this principle may be 

 applied, as for most purposes an axle with 

 an undivided curve surface (as in fig. 1) will 

 serve as well, or better. 

 Fig. 6 shows how to 

 construct the thi-eads of 

 screws according to this 

 princi|ile. The propor- 

 tions I prefer are — 

 nb onc-fourtli of a c ; 

 a c one-fourth, sixth, 

 eighth, tenth, or twelfth 

 of the diameter. 



As a further illustra- 

 tiim of the variety of 

 contrivances to the 

 construction of which 

 tlie descrilied principle 

 may lie iiscfully applied, 

 1 will luime the follow- 

 ing: — Curve-shaped re- 

 volving valves (instead 

 of flat ones) for regu- 

 lating tlie quantity of 

 steam let into the cy- 

 linders of locomotive 

 engines.— Similar valves 

 (instead of slide valves) for steam-engines, which applied to either 

 end of the cylinder, wcuild cause a considerable saving of steam, — 

 as in many engines (for instance, those on railways) a great deal 

 of steam in tjie canals is now lost. — A revolving motion, varying in 

 speed, would be better than the motion given by an eccentric. — 



Fig. 4. 



