HYDBAULIC RAM 685 



increases, the time of opening will tend to increase slightly as the weight 

 increases, and will also increase with the travel of the valve. For 

 all practical purposes, however, the opening may be considered as 

 instantaneous. 



The period during which the valve is full open depends entirely on the 

 time necessary to produce the required velocity of flow along the supply- 

 pipe, and will therefore increase with the weight of the valve, and with 

 the ratio of length of supply pipe to supply head. 



Thus let : 



C a = area of supply pipe in square feet. 

 H = supply head m feet. J ^ = effective discharge ^ Q 



l = lengThof supply pipe. I = actual discharge area multiplied by the co- 

 V efficient of discharge. 



Then on the assumption of instantaneous opening of the waste valve, 

 the velocity of flow in the supply pipe after t seconds is given by 



l-e 



2^ [ ft. per sec. 



' 



(equation 12", p. 242). 



/ 2<y H 1 



where c= A/ fl a v *; and k = 21^ . , .fl a*: 



J- ~~T~ n" d L ~T~ . o 



7?i a* m a* 



Experiments l show that this formula gives results in close agreement 

 with those obtained in practice. 



The weight of the valve is then adjusted so as to give v a value which, 

 for most efficient working, is approximately '4 \/J^ feet per second. 



The time which the valve takes to close cannot be calculated with any 

 pretension to accuracy. It will evidently depend largely on the form of 

 the valve body and of the valve box, and will increase as the lift of the 

 valve, and its weight, increase. 



The total time during which it remains off its seat will thus increase with 

 the delivery head and with the length of supply pipe, arid will diminish 

 as the ratio H -r- I increases, also increasing with its weight and lift. 



The time during which it is on its seat increases with the distance 

 from valve seat to delivery air chamber, and increases as the delivery 

 head increases, since the first of these factors regulates the time taken by 

 the reflex pressure wave to reach the waste valve, and the second regulates 

 the time at which the delivery valve closes, and hence the time of 

 initiation of this reflex wave. 



1 Harza. Bulletin of the University of Wisconsin. No. 205, p. 211, 



