WATER METERS 727 



fitted to the rams of 5 testing machines showed the following friction 

 losses : 



Experiments by S. L. Davis 1 on a 5 inch testing machine ram carrying 

 a U leather at its lower end and working in a copper lined cylinder 

 showed that after a fair amount of service the friction, with increasing 

 loads, varied irregularly from about 5 per cent to zero, with a mean value 

 of 1*3 per cent., the pressure meanwhile increasing from 500 to 4,500 Ibs. 

 per square inch. With diminishing loads the friction had a maximum 

 value of 3*6 per cent, at the lowest pressure, with a mean value of '2 per 

 cent, over the whole range. 



For satisfactory working the U leather should have a ring of metal or 

 other material inserted between the flaps, and should as far as possible 

 have a metal backing over its curved portion. 



Experience shows that a narrow fitting strip not above J inch wide 

 is preferable to one which is wider, since, owing to the reduced tendency 

 to bending at the bottom of the U with a shallow collar, the leather is not 

 so liable to crack. 



Hemp packing is also used to a limited extent for hydraulic glands. 

 Here the percentage loss in friction decreases with an increasing load, 

 but since the packing must be tightened so as to prevent leakage at the 

 highest pressures to which it may be subjected, the loss at low pressure 

 is probably three to four times that of a leather collar. 



AKT. 196. WATER METERS, 



It is usually important that the volume of water supplied for domestic 

 or power purposes should be accurately measured, and various meters have 

 been devised for this purpose. 



These may be divided into the following classes : 



(1) Low pressure meters. 



(2) Inferential meters. 



(3) Positive meters. 



i Engineering News, Feb. llth, 1909, p. 167* 



