WATER, METERS 731 



at A, and surrounds the inner casing shown in section at 13. It then 

 finds its way through two inclined ports in this casing, and, impinging 

 on the vanes of the fan F, drives this around with a velocity which 

 depends on the flow of water, and which is recorded on the dial worked 

 by its spindle and worm gear, afterwards escaping through the ports D 

 and pipe E. To prevent overrunning, eddy formation is fostered by a 

 series of recesses formed around the inside of the inner casing, and by 

 baffles above the fan at (7. To reduce friction at the lower footstep bearing 

 an oil reservoir is provided in the hollow spindle of the fan. 



(3) The Positive Meter consists of a small hydraulic engine, either of 

 the rotary or reciprocating piston type. All the water to be measured 

 passes through the cylinder or cylinders of this engine, and its volume 

 is taken as that of the piston displacement. 



The number of revolutions or strokes of the piston being registered 

 on a recording apparatus, this is easily arranged to record the volume 

 passed. 



The rotary type is common in the United States of America, and, as 

 usually made, consists of a casing of gun-metal or vulcanite, in which 

 works a rotary vulcanite piston. This has no means of compensating for 

 wear, and, as thus constructed, is very unreliable for small flows, even when 

 new. After being in use for some time the increased leakage past the 

 piston renders it still less reliable. 



The Kent " Uniform " meter (Fig. 352) is one of the best of this type, 

 and here compensation is made for the effect of weai\of the rotary piston P 

 by an adjustable metal tongue S. In this meter water is admitted at A 

 and fills the casing around the working chamber B. The vulcanite piston 

 P, elliptical in section, rotates and slides freely, but without play, on the 

 fixed hub Q, which is itself eccentric with respect to the working chamber. 

 The piston carries a central pin which describes a circular path as rotation 

 takes place, and which actuates the recording mechanism. 



The bottom ports at C are in free communication with the chamber B t 

 and the action of the meter is as follows : 



Assuming the piston to be in the position shown in dotted lines, water 

 is admitted through these ports and the upper port D, to the space between 

 the chamber, the piston, and the tongue S, and to the interior of the 

 hollow piston, thus exerting a pressure between the hub and the inside 

 of the inner end of the piston, as well as on the outside of the piston 

 from C to S, and driving the latter round in a clockwise direction. At 

 the end of half a revolution the other end of the piston becomes the driver 

 and so on. 



