Dairy processing: Aseptic processing and packaging systems
Flow control device (FCD)

General conditions

• Is constructed of stainless steel and is in good mechanical and sanitary condition
• The driving mechanism is designed so that in the case of wear, belt stretch, the capacity will not increase
• The flow control device cannot be excluded from the system during operation of the APPS
• Is located upstream from the holding tube, normally between the outlet of the raw regeneration section and the inlet of the heating section of the APPS

Set and sealed

• Set the maximum operating capacity of the flow control device to ensure an appropriate flow rate to give the proper holding time, in accordance with the calculations done in the scheduled process (refer to Holding verification)

When homogenizers are located within the aseptic system:

• Make the flow rate evaluations with these pieces of equipment operating (with no valve pressure on the homogenizer) and by-passed to determine the fastest flow rate (minimum holding time)

When flow promoters are located downstream from the flow control device:

• Determine the flow rate with the flow control device operating at maximum capacity and the flow promoters in operation

If the device is of the variable speed type or a single speed capable of being altered with different belts and pulleys:

• Seal the flow control device at an established flow rate to prevent operation at a greater capacity than that which gives the proper holding time
  • on meter based timing systems, seal the access to the alarm settings for flow diversion set points
  • a seal is not necessary if maximum speed gives legal holding time

Any change in the line resistance of the system after maximum speed of the pump has been set, will alter the flow rate and corresponding hold time. Increasing the line resistance by the addition of plates or piping will decrease the flow rate, increasing holding time. This increase in flow resistance in effect reduces the efficiency of the sterilizer. Decreasing the line resistance by the removal of plates, pipes, or auxiliary units will increase the flow rate, decreasing the holding time. Wear of the drive belts and pump impellers due to normal operation will gradually decrease the rate of flow through the system, thereby increasing the holding time.

• Evaluate and seal (if necessary) the flow control device upon installation and annually thereafter; and in addition, whenever the seal on speed setting is broken, whenever any alteration is made affecting the holding time, the velocity of the flow (such addition or removal in the number of plates, pipes or auxiliary units) or the capacity of the holding tube or whenever a check of the capacity indicates a speed up
• Keep records of alteration and re-evaluation of the system on file

Fail safe capability

• Ensure there is no by-pass (recirculation line) around the flow control device during processing
  • use a proximity switch so that the flow diversion device will not operate in forward flow
  • a by-pass may be present for CIP purposes as long as it is dismantled and removed during processing

When a meter based timing system replaces the positive displacement flow control device:

• Ensure it has the appropriate controls and instrumentation in place, as outlined in Appendix C: Meter based timing system
• Evaluate it upon:
  • installation and at least once every 6 months thereafter
  • when the seal on the flow alarm is broken
  • when any alteration is made affecting the holding time, the velocity of the flow or the capacity of the holding tube
  • when a check of the capacity indicates a speed-up
• Keep records to show testing has occurred