16. Calibration of Turbines, Pumps, Gates, and Valves

Some irrigation distribution systems may require measurement of the flow by means of the turbines, pumps, gates, or valves through which the water flows. This measurement may be done if the structure is calibrated in the field using an approved flow measuring method or in the laboratory using hydraulic models. Properly prepared calibration curves are a reliable means for obtaining accurate discharge measurements.

Discharge is generally related to power in the case of turbines or pumps. The relationships may be determined by measuring the average power output or input during the period in which discharge measurements are made for various load conditions. Curves or tables are developed from these test data to show the rate of flow that occurs for specific power and operation conditions. Long- or short-term deterioration or damage may change machinery efficiency. Thus, these calibrations should be periodically checked, adjusted, and recalibrated as needed.

For gates and valves, discharge-versus-gate-opening curves for various appropriate heads are desired. These curves may be determined by measuring the rates of flow at given gate or valve openings under specific head conditions. By operating over the full range of openings and heads, data may be obtained for establishing the families of curves. Generally, the curves would show the rates of flow in cubic feet per second (ft3/s) that occur through the gate or valve at specific openings, which are expressed in percent of opening, for the pertinent operating heads. These curves may also be prepared from model test data.