Calibration equations for submerged segmental orifice flowmeters

Abstract

Regression equations for the calibration curves of submerged segmental orifice flow-meters suitable for use in flood irrigation experiments are given. hfeter diameters ranged from l 1/4 inches to 6 inches and all had a throat width to diameter ratio of 0.64. The calibration equations were of the general type Q = aH0.5,, where Q is the flow rate in cusecs, H is the head loss across the meter in inches and a is a coefficient dependent on the area of the orifice. The relationship between coefficient a and orifice area A in square inches was linear, the regression equation being a = 0.0040 + 0.0113A. The regression equation between coefficient a and meter diameter D in inches was a = 0.00704D1.92 The two relationships enable the calibration curve for any meter between l$ and G inches diameter and with a throat width to diameter ratio of 0.64 to be predicted with a maximum error of per cent. Experience with the meters in the field has shown that the flow-meters need to be constructed out of materials with smooth surfaces. Rigid PVC plastic piping has this characteristic and the added advantages of being light, easily handled, and corrosion resistant. Details of installation in the field are also given.