738 



HYDRAULICS AND ITS APPLICATIONS 



respectively to the upstream and throat chambers of the tube. Each 

 contains a float, and these are connected by means of wire cords to a 

 differential gear consisting essentially of three bevel wheels A, B, and C 

 of which the motions of the two equal wheels A and C are controlled by 

 the floats, while B is carried on an axis attached to a loose sleeve. 

 Evidently if the wheels A and C revolve in opposite directions owing to 



the water columns rising or 

 falling together, 'the wheel B 

 will simply revolve on its axis. 

 Any alteration in the relative 

 1 3vel, however, causes the wheel 

 B and the sleeve on which it is 

 mounted to rotate about the 

 axis D, and thereby to produce 

 a vertical movement of the rack 

 E, which gears with a pinion J 

 mounted on the outer end of 

 the sleeve, and which carries 

 the recording pencil P at its 

 upper end. The recorder may 

 be arranged to indicate either 

 the velocity of flow and there- 

 fore the discharge at any 

 instant, or the total discharge 

 of the meter. In the former 

 case the pencil traces out a 

 curve on a sheet carried by a 

 vertical drum driven at a con- 

 stant rate by clockwork, this 

 paper being ruled with hori- 

 zontal lines the distances of 

 which (representing equal in- 

 crement of velocity) from the 

 zero line, are proportional io+/Ji. Where it is required to have an 

 automatic record of the discharge as well as a record of the rate 

 of flow, an ingenious integrating device is used. This consists of an 

 additional drum concentric with the recording drum and rotated uniformly 

 usually once in 10 minutes by clockwork. The surface of this drum 

 is in two planes ; one of the full diameter of the drum, and the other of a 

 reduced diameter forming a recessed surface. The boundary curve of the 



To Float Mechanism 



Fio. 358. Integrating Mechanism for Venturi 

 Meter. 





