Centrifugal pump suction overpressure

rppearso

What would cause rupture disks on a high DP centrifugal pump suction to pop every time the pump is shut down. The discharge SDV's take 30 sec to 1 min to close so there is not a water hammer issue, the recycle valves are fast opening but they discharge back to the surge tank so they are not in the flow path of the rupture disk.

The only other thing I could think of would be a check valve failure or the recycle line is undersized.