Dairy processing: Aseptic processing and packaging systems
Flow diversion device (FDD)

General conditions

• The flow diversion device design permits sterile operations and prevents potentially unsterilized product from contaminating the fillers or aseptic surge tank(s)
• The flow diversion device and the return lines are constructed of stainless steel and are clean and in good mechanical condition
• The valves, plunger seals and O-rings are clean and in good mechanical condition
• Stem length of the valves is non-adjustable (this ensures that proper seating of the valves is not disturbed)
  • if the stem has a threaded attachment, use a locking pin or other equivalent locking mechanism to prevent any misalignment
• The air to the flow diversion device is clean and unrestricted
• The flow diversion device is equipped with a proper control panel where the control functions and relays are installed
  • the control panel may be part of a universal panel unit
  • it is free of any device or switches that could override the control functions and jeopardize the safety of sterilized product
  • on valves that have external solenoids, the air lines do not have quick release couplings

Installations on APPS often have operating parameters for the flow diversion device that are so complex they can only be handled by a micro-processor or programmable logic controller (PLC).

• A PLC or micro-processor control used strictly for flow diversion device function does not need to meet the criteria in Programmable logic controllers but ensure all valve functions meet the test standards

Return line

• The flow diversion device has a pipeline that directs the flow of potentially unsterile product safely away from fillers and /or aseptic surge tanks
  • any subsequent valves installed on this line are configured in all positions to allow free flow from the flow diversion device, without blocking the flow or creating excessive back pressure on the flow diversion device
• Install a flash cooler on the return line to prevent injury to bystanders during divert events when pre-sterilizing the system

Location

• The flow diversion device is located after the final cooling section and before the fillers or aseptic surge tanks
  • this is necessary since diverting hot product right after the holding tube could result in flashing in the divert line

Fail safe divert capability

Indirect heating systems:

• Ensure the flow diversion device automatically assumes the divert position (so product will not go to aseptic surge tanks or fillers) under at least one of the following conditions:
  • product temperature in the sensing chamber drops below the specification in the scheduled process
  • differential pressure between sterilized product and unsterilized product or heat transfer media is less than 14 kPa (2 psi) in the regenerator
  • adequate product pressure is not maintained in the holding tube to prevent boiling (less than 69 kPa (10 psi) above the boiling pressure of the product in the holding tube)
  • loss of electrical power or compressed air to the flow diversion device solenoids
  • excessive flow rate is detected for systems utilizing a magnetic flow meter as a flow control device
  • pressure in the surge tank drops below the value specified in the scheduled process, in systems where there is only one surge tank or no capability to send product directly to a filler (prevents sterile product from entering unsterile tank). Note: In systems where more than one surge tank exists, product would not need to be diverted but could be directed to the sterile surge tank.

Direct heating systems:

• Ensure the flow diversion device automatically assumes the divert position (so product will not go to aseptic surge tanks or fillers) under at least one of the following conditions:
  • product temperature in the holding tube drops below the specification in the scheduled process
  • differential pressure between sterilized product and unsterilized product or heat transfer media is less than 14 kPa (2 psi) in the regenerator
  • adequate product pressure is not maintained in the holding tube to prevent boiling (less than 69 kPa (10 psi) above the boiling pressure of the product in the holding tube)
  • loss of electrical power or compressed air to the flow diversion device solenoids
  • for steam infusion systems, loss of pre-determined parameters (for example, temperature, pressure level, as specified in the scheduled process) at the steam infusion chamber exits
  • for steam injector systems, improper differential pressures across the steam injectors at the holding tube (less than a 69 kPa (10 psi) drop across the injector)
  • excessive flow rate is detected for systems utilizing a magnetic flow meter as a flow control device
  • pressure in the surge tank drops below the value specified in the scheduled process, in systems where there is only one surge tank or no capability to send product directly to a filler (prevents sterile product from entering unsterile tank). Note: In systems where more than one surge tank exists, product would not need to be diverted but could be directed to the sterile surge tank.
• Install the flow diversion device with position detection capabilities to provide an electrical signal to the safety thermal limit recorder flow indicating lights and event pen
• Re-sterilize all product contact surfaces downstream from the holding tube after an event causing a flow diversion, as outlined in the scheduled process (see also the section on Thermal limit controller sequence logic)
  • the re-sterilization process includes the fillers and aseptic surge tanks, unless there is an aseptic barrier to act as a leakage barrier (see section Leak detect and Appendix G: Preventing cross connections)
• Test the operation of the valves using the procedures in Critical process test procedures - Flow diversion device.
  • keep records to show testing has occurred
  • follow-up on out-of-specification findings

Leak detect

In APPS where the filler continues to operate from an aseptic surge tank while the flow diversion device is in the divert position:

• use an aseptic barrier to separate sterile product from potentially non-sterile product (see Appendix G: Preventing cross connections)
• locate this aseptic barrier between the flow diversion device and the blocking valve for the aseptic surge tank
  • the barrier(s) may include one or more steam blocks
• include a resistance thermal device or other suitable temperature sensor at the lowest level of the barrier to detect barrier failure due to steam loss or fluid leakage into the barrier
• if barrier failure is detected by the temperature sensing device, ensure an alarm system is triggered to alert the operator to the alarm condition, immediately initiating a "shut down sequence" for the processing system as specified in the scheduled process

After a barrier failure condition:

• drain the fillers, aseptic surge tanks and lines, and aseptic processing system of product completely
• re-sterilize all equipment before processing and filling resumes
  • implicated product should be placed on hold until its sterility is assessed
  • note this failure in the operator's log book and complete a process deviation report, including the date and time of the process deviation, investigation into the cause of the process deviation and action taken both on product and other corrective measures

Sealed

• Seal the flow diversion device control panel and valve position detector cover(s) to prevent unauthorized tampering or adjustments
• Seal the valve position sensing detectors, valve actuating solenoids and relays
• Seal the access to programming functions when a PLC or micro-processor is used to control valve functions