Dairy Establishment Inspection Manual – Chapter 17 - Higher Heat Shorter Time (H.H.S.T.) Processing and Extended Shelf-Life (ESL) Dairy Products
1.17.09 Flow Diversion Device (FDD)

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The FDD is set up to control the direction of product flow according to the establishment of safe conditions within the processing system. It is located downstream from the regenerator section, and is designed to automatically divert flow away from the surge tank or filler.

1.17.09.01 General Conditions

The FDD must be of a design that can positively and effectively prevent potentially unpasteurized product from contaminating the fillers or surge tank(s).

All FDDs used in continuous H.H.S.T. processing systems used to pasteurize ESL products stored under refrigerated conditions must have one of the following acceptable designs:

  1. Dual-stem type FDD incorporating two three-way valves in series. These dual stem flow diversion devices shall have a leak detect line separate from the divert line, that is free draining from the lower port of the leak detect valve back to the constant level tank or other acceptable receptacles;
    or
  2. Steam-block type FDD system. This is comprised of a divert valve and one or more steam-block valves:
    1. The divert valve shall be fail-safe, position detectable and equipped with means to provide an alarm and protection when required
    2. The steam block valve shall have continuous supply of steam and a continuous visible bleed of steam or condensate to the drain
    3. The steam block valve shall be equipped with an interlocked resistance thermal device (RTD) located at the lowest level of the barrier to detect any fluid leakage into the barrier. If the leakage is detected by the temperature sensing device, an alarm or other appropriate system must alert the operator to the steam barrier failure. Appropriate action as indicated by the scheduled process deviation procedure must be followed.

A steam barrier is not mandatory, however if an establishment does not have a dual-stem type FDD incorporating two three-way valves then they must have a steam barrier.

Dual Stem FDDs must be equipped with a proper control panel where the control functions and relays are installed. This control panel may be part of a universal panel unit. This panel shall be free of any device or switches that may override the control functions and jeopardize the safety of pasteurized product. On valves that have external solenoids, the air lines must not have quick release couplings.

Installations on H.H.S.T. processing systems often have complex operating parameters for the FDD that can only be handled by a micro-processor or programmable logic controller PLC). A PLC or micro-processor control used strictly for FDD function is not required to meet the standards of Task 1.17.11.07 - Program Logic Controllers and Computers, but all valve functions must pass the required tests.

The FDD and the return lines shall be constructed of stainless steel and must be clean and in good mechanical condition. Valves, plunger seals and "O"-rings must also be clean and in good mechanical condition. Stem length of the valves shall be non-adjustable to insure that proper seating of the valves is not disturbed. If the stem has a threaded attachment, a locking pin or other equivalent locking mechanisms shall be used to prevent any misalignment. Air to the FDD must be clean and unrestricted.

1.17.09.02 Return Line

The FDD shall have a pipeline that directs the flow of potentially unpasteurized product safely away from surge tanks and /or fillers. Any subsequent valves installed on this line must be configured in all positions to allow free flow from the FDD, without blocking the flow or creating excessive back pressure on the FDD. A flash cooler may be installed on the return line to prevent injury to bystanders during divert events when pasteurizing/sterilizing the system.

1.17.09.03 Location

The FDD must be located downstream from the regeneration and before the surge tanks or fillers.

1.17.09.04 Fail Safe Divert Capability

The FDD shall automatically assume the divert position (so product will not go to the surge tanks or fillers) under at least one of the following conditions for indirect heating systems:

  1. The product temperature in the sensing chamber drops below the specification in the scheduled process;
  2. The differential pressure between pasteurized product and unpasteurized product or heat transfer media is less than 14 kPa (2 psi) in the regenerator;
  3. 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);
  4. Loss of electrical power or compressed air to the FDD solenoids;
  5. Excessive flow rate is detected for systems utilizing a magnetic flow meter as a flow control device;

The FDD shall automatically assume the divert position (so product will not go to the surge tanks or fillers) under at least one of the following conditions for direct heating systems:

  1. The product temperature in the holding tube drops below the specification in the scheduled process;
  2. The differential pressure between pasteurized product and unpasteurized product or heat transfer media is less than 14 kPa (2 psi) in the regenerator;
  3. 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);
  4. Loss of electrical power or compressed air to the FDD solenoids;
  5. For steam infusion systems, loss of pre-determined parameters (temperature, pressure level, etc. as determined by the process authority) at the steam infusion chamber exits;
  6. For steam injector systems, improper differential pressures across the steam injectors at the holding tube (a 69 kPa (10 psi) drop across the injector is required);
  7. Excessive flow rate is detected for systems utilizing a magnetic flow meter as a flow control device.

The FDD shall be installed with position detection capabilities to provide an electrical signal to the S.T.L.R. or legal panel.

After an event causing a flow diversion, all product contact surfaces between the holding tube and the FDD shall be held at or above the required pasteurization or sterilization temperature continuously and simultaneously for at least the required pasteurization or sterilization time, as outlined in the scheduled process (see also Task 1.17.11.04 - Thermal Limit Controller Sequence Logic). During CIP and pasteurization cycles of the H.H.S.T. processing system, a properly designed valve system must be used in accordance with Appendix 19 - 10 to prevent cross-contamination of pasteurized finished product in surge tanks with chemical cleaning solutions.

Plant records shall indicate the test results for valve operation at the required intervals and must show satisfactory follow-up on out-of-specification findings.

1.17.09.05 Leak Detect

H.H.S.T. systems where the filler continues to operate from a surge tank while the FDD is in the divert position, and the FDD is a steam-block type, must use a properly designed aseptic barrier system to separate pasteurized product from potentially under processed product. This segregating valve system shall be located between the FDD and the surge tank. An aseptic barrier system is not mandatory for systems that use a dual-stem type FDD valve assembly.

The barrier(s) may include one or more steam blocks, but must include a resistance thermal device (RTD) or other acceptable temperature sensor at the lowest level of the barrier to detect barrier failure due to steam loss or fluid leakage into the barrier. Barrier failure detected by the temperature sensing device must trigger an alarm system 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, the fillers, surge tanks and lines, and H.H.S.T. system must be completely drained of product and all equipment must be re-pasteurized or re-sterilized before processing and filling may resume. Implicated product should be placed on hold until its pasteurized condition is assessed. This failure must be noted in the operator's log book and a process deviation report must be completed, which includes 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.

1.17.09.06 Device Sealed

The FDD legal panel and valve position detector cover(s) must be sealed to prevent unauthorized tampering or adjustments. The valve position sensing detectors, valve actuating solenoids and relays shall be sealed. If a PLC or micro-processor is used to control valve functions, access to programming functions shall be sealed.

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