We are having a problem with the product fractionator bottoms pump (multistage centrifugal Pump turbine driven/standby motor driven)(inlet ~330 deg C) of a MHC unit; whenever the pump is taken in service and made ready after maintenance and primed (previously used to prime from the suction valve, now try to prime with a warm-up line) the downstream fired heater (thermal cracker) trips due to low flow as soon as the suction valve is crack opened to take it in service.
Any suggestions on how to rectify this issue?