Dairy Establishment Inspection Manual – Chapter 17 - Higher Heat Shorter Time (H.H.S.T.) Processing and Extended Shelf-Life (ESL) Dairy Products
1.17.06 Flow Control Device (F.C.D.)
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This task governs the uniform rate of flow through the holding tube so that every particle of product is held for the required period of time, as specified in the scheduled process. This device is a positive displacement type pump or homogenizer. Other equally effective mechanisms such as a Meter Based Timing System (MBTS) with proper components (centrifugal pump, flow control device or variable speed motor, meter head, relays, alarms and flow recorder-controller, etc.) may also be used as a flow control device. Refer to Appendix 19-4 for more information on MBTS.
1.17.06.01 General Conditions
The flow control device must be constructed of stainless steel and be in good mechanical and sanitary condition. The driving mechanism shall be designed so that in the case of wear, belt stretch, etc. the capacity will not increase. The flow control device cannot be excluded from the system during operation of the H.H.S.T. processing system. The device must be located upstream from the holding tube and normally it is located between the outlet of the raw regeneration section and the inlet of the heating section of the processing system.
1.17.06.02 Set and Sealed
The maximum operating capacity of the flow control device shall be set to ensure an appropriate flow rate to give the proper holding time, in accordance with the calculations done in the scheduled process, as evaluated under task 1.17.08.03 Holding Verification and Records.
When homogenizers are located within the H.H.S.T. system, flow rate evaluations shall be made 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, the flow rate shall be determined with the flow control device operating at maximum capacity, and the flow promoters in operation.
If maximum speed gives legal holding time a seal is not necessary. If the device is of the variable speed type or a single speed capable of being altered with different belts and pulleys, it must be sealed at an established flow rate to prevent operation at a greater capacity than that which gives the proper holding time. Alarm settings determining the flow diversion set points on magnetic flow meter systems must also be sealed.
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 pasteurizer. 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.
The flow control device is to be evaluated and sealed (if necessary) 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. Records of alteration and re-evaluation of the system must be kept in the plant's file.
1.17.06.03 Fail Safe Capability
There must not be a by-pass (recirculation line) around the flow control device during processing. A by-pass may be present for C.I.P. purposes, but must be dismantled and removed during processing. To ensure that no by-pass is present during processing a proximity switch should be utilized so that the F.D.D. will not operate in forward flow. A Meter Based Timing System must have the appropriate controls and instrumentation in place, as outlined in Appendix 19-4. When a Meter Based Timing System replaces the positive displacement flow control device, it must be evaluated upon installation and at least once every 6 months thereafter, whenever seal on the flow alarm is broken, whenever any alteration is made affecting the holding time, the velocity of the flow or the capacity of the holding tube or whenever a check of the capacity indicates a speed-up. Appropriate records must be kept to show proper testing has occurred.
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