What's wrong with the selection of regulating valve with too large or too small caliber?

If the diameter of the regulating valve is too large and the throughput is small, the outlet pressure will be unstable. Because if you open it a little, the downstream consumption will be satisfied, and the valve port will be closed and then opened immediately, and the downstream pressure will surge. If the valve diameter is too small, the flow of the regulating valve through the valve port will increase and the noise will also increase. Because of the large flow rate, the valve port where gas flows will be worn and washed away, and the service life of the control valve will be greatly shortened!