Determination of Discharge Coefficient for Ball Valves With Calibrated Inserts

The valve coefficient was measured for 1/2-, 3/4- and 1 nominal ball valves. It was desired to use a recently designed orifice insert with these valves to obtain smaller valve coefficients. Orifice inserts were placed into the body of a threaded ball valve just upstream of the spherical control element. The valve coefficient was measured for each insert, and an expression was determined to relate the orifice diameter to other pertinent flow parameters. Two groups were chosen to correlate the collected data, and a graph was developed. These results can be used as an aid in sizing the orifice insert needed to obtain the desired valve coefficient. The study has shown that a two parameter power law equation can be used as an aid in predicting the desired results. Knowing pipe size and schedule, the diameter of the orifice insert needed to obtain the desired valve coefficient can be approximated with minimum error. An error analysis performed on the collected data shows that the results are highly accurate, and that the experimental process is repeatable.