Preventing water hammer at the main propellant valves in a liquid rocket engine test cell? Any solutions that doesn't require additional valves?

It's critical that the main valves close rapidly, but the concern arises with water hammer ever since the test cell has been upgraded to support higher pressure flow. Easy solutions that I can think of is by adding a valve/volume somehow that opens in sync with the main_valves_close. I thought of relieving pressure at the tanks right before the main valves close, but that seems too scetchy. Any guidance would be appreciated.