Question

In case if pasteurization temperature is not attained, FDV diverts the flow of milk to which of the following section?

• A. Regeneration section
• B. Balance tank
• C. Raw milk silo
• D. Heating section

Hint:

The Flow Diversion Valve (FDV) is a safety device that diverts under-pasteurized milk back to the raw milk balance tank to prevent under-processed product from entering the pasteurized storage lines.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Continuous High-Temperature Short-Time (HTST) pasteurizers are equipped with safety controls to ensure all processed milk receives the required thermal treatment.
The Flow Diversion Valve (FDV) is a key safety device located at the outlet of the holding tube.

Step 2: Detailed Explanation:
During HTST pasteurization, milk must be heated to at least 72$^{\circ}$C and held for 15 seconds.
A temperature sensor at the outlet of the holding tube monitors the milk temperature.
If the milk temperature falls below the setpoint (e.g., 72$^{\circ}$C), the controller triggers the Flow Diversion Valve:
1. Forward Flow: Under normal operating conditions, the FDV remains open to forward flow, allowing pasteurized milk to proceed to the regeneration and cooling sections.
2. Diverted Flow: If the temperature falls below the limit, the valve switches to diverted flow.
The sub-temperature milk is diverted back to the raw milk balance tank (constant level tank) at the inlet of the system.
Returning the under-pasteurized milk to the balance tank prevents it from mixing with pasteurized milk in the regeneration section and ensures it will be re-processed.
Diverting the milk to other sections like the raw milk silo is avoided to prevent thermal contamination of the bulk raw milk supply.
Diverting directly to the heating section is avoided because the milk must first pass through the balance tank to maintain steady system pressures and feed rates.

Step 3: Final Answer:
Therefore, the FDV diverts under-pasteurized milk back to the balance tank.