Hydraulic Experiments on Pressure Dissipation with Orifices in Conduit

Pressure dissipation in closed conduit used in irrigation system (I)

Abstract

The effect of pressure dissipation with orifices can be applied to an accurate and convenient means of pressure control in closed conduits.In this application, it is necessary to avoid cavitation.
From the viewpoint of dividing the required amount of pressure dissipation among multiorifices, hydraulic experiments and considerations were made on the characteristics of orifices.
The results are as follows:
1) When orifice diameter to pipe diameter ratio β is within the range of 0.2≤β≤0.6, incipient cavitation index σ_i and critical cavitation index σ_c are given in the following equations respectively.
σ_i=4.5β+0.5
σ_c=3.3β
2) When the value of cavitation index σ is greater than that of critical cavitation index σ_c, the recovery of pressure is achieved at 4D-5D and pressure fluctuation in downstream is small.Where, Dis pipe diameter.
3) When two orifices at intervals of 5D are arranged in series and each cavitation index of these orifices is σ>σ_c, the value of pressure dissipation for each orifice can be estimated by Gardel's equation.
4) When two orifices are arranged in series, orifice diameter to pipe diameter ratio of the orifice settled in upstream should be a little smaller than that in downstream. After this condition is satisfied, each orifice has much the same degree of safety against cavitation occurrence.