672 REPORT — 1882. 



8. On the Engine Poiuer Meter. By C. Vernon Bots. 



The quantity of work done by steam or other fluid on the piston of an engine 

 is found l)y niiiltiplyin<r at every moment the rate of movement of the piston by 

 the difference of pressure on its two sides, and continuously adding the products. 

 This quantity is usually determined in any one complete stroke of an engine by 

 finding the areas of the indicator diagrams taken at each end of the cylinder, and 

 adding them together. This is a measure of the whole work done in that stroke. 

 In the same wav the work done in any other stroke may be determined. If the 

 en<nne is working any length of time at a uniform rate against a constant load, 

 tlie total quantity of work done in that time may be found by midtiplyiDg the 

 number of strokes by the work done in one. Practically this cannot be done ; 

 therefore, if it is desired to find the work done during aiiy length of time, some 

 form of engine-power meter must be used. At the present time, when the efficiency 

 of machines is attracting so much notice, any advance in this direction is of 

 importance. 



In the author's instrument the difference of steam-pressure is determined by a 

 differential pressure gauge, consisting of a piston in a cylinder controlled by a 

 spring. The two ends of the cylinder communicate by pipes with the two ends of 

 the cylinder of the engine. This cylinder is separated from the box containing the 

 calcijating mechanism by an air space, so that heat and dirt are effectually 

 excluded. The piston rod enters the box at the middle of the base, and passes 

 through to the top, where the spring is attached which lies in a tube attached to 

 the top of the box. On the piston rod is a sleeve carrying two pins, one working 

 in a guide to prevent the sleeve from turning when the piston rod turns slightly, 

 and the other to give inclination to what is called the tangent wheel. This is a 

 .small wheel with its edge in contact with the surface of a cylinder which is free to 

 travel longitudinally and to rotate. If the plane of the tangent wheel is parallel 

 to the axis of the cylinder, then when the latter moves longitudinally, there will be 

 no rotation, but if the tangent wheel is inclined, the cylinder will rotate v/itli a 

 speed proportional to the tangent of the inclination multiplied by the rate of the 

 longitudinal movement. If the pin on the sleeve of the piston rod works in a 

 radial slot in the tangent wheel frame, then the tangent of the inclination of the 

 latter will alwavs be proportional to the displacement of the piston rod, and 

 therefore to the difference in pressure in the engine cylinder. Now if the integi-at- 

 ing cylinder is moved in time with, and in proportion to the motion of the engine- 

 piston, the rate of turning of the integrating cylimler will be proportional to the 

 rate at which work is being done, and the number of turns shown by a counter 

 will be a measure of the total amount done during any length of time. There is 

 no necessity to adjust the tangent wheel to absolute parallelism with the axis of the 

 cylinder when there is no steam-pressure ; even if considerably inclined, there will 

 be no accumulating error, for whatever error is introduced during a forward .stroke 

 is absolutely removed during the return stroke. 



/ 



The following Report and Papers were read -.—r 



1. Report of the Committee on Screw 6aur/es. — See Reports, p. 311. 



2. Torpedo-hoats. By J. Donaldson, M.I.G.E.^ 



The author pointed out the great advance tbat had been made in the con- 

 struction and armament of torpedo-boats since the American ("ivil War, and the 



' Published in. extenso in the Engineer Sept. 29, and in Engineering October 

 13 and 20. 



