You are right in that water hammer occurs when you close a valve. When you open a valve, I think you have a loose washer in a valve that is sticking and restricting the flow. Replace the valve or the washer and possibly the seat inside of it. Sometimes the screw on the washer comes loose. Sometimes it can be cause by a remote valve that was recently opened and closed such as the main valve.
Throttling a valve by closing it down will only cause it to get worse. Valves are made to be open or closed and partially open valves will suffer premature failure by washing out. They make a special globe valve they use as a pressure reducing valve to go in your main line if you have too much pressure.