Tuning an Irrigation Valve Using Flow Control Like any car, boat, or motorcycle, valves require periodic tune-ups to perform at their best. It’s easy to tune a Hunter valve using flow control. You can make minor adjustments to help your Hunter PGV, ICV, and IBV Valves open and close more efficiently by using the flow control feature located at the top of each valve. As long as all the Hunter valves on a site are properly sized, you can use the convenient flow control feature on your valve to make minor adjustments to optimize the efficiency of your irrigation system.