Question 30 QMED02 - Electrician-Refrigerating Engineer

The Correct Answer is C **Explanation for Option C (valves "4" and "14"):** The device shown in illustration GS-0153 is typically a filter unit (often a multimedia or sand filter). "Backflush mode" is a cleaning process where the flow of water is reversed through the filter media to dislodge accumulated debris and flush it out to waste. 1. **Valve "4" (Influent/Inlet Valve):** During normal filtration, water enters the unit through this valve. In backflush mode, water must still enter the unit to perform the cleaning action. Therefore, valve "4" must be **open**. 2. **Valve "14" (Backwash Waste/Drain Valve):** In backflush mode, the dirty water (containing the flushed-out debris) exits the filter unit through the drain or waste line. Valve "14" controls this flow and must therefore be **open** to allow the waste water to leave the system. Thus, for the unit to successfully operate in backflush mode, the influent flow (4) must be open, and the backwash waste flow (14) must be open. **Explanation for Incorrect Options:** * **A) valve "4":** This is insufficient. While valve "4" must be open to let water in, the dirty water has nowhere to exit the system if the drain valve (14) is closed. * **B) valves "4" and "5":** Valve "5" typically controls the effluent/filtered water outlet line (the clean water outlet). During backflush, the clean water outlet must be **closed** to force the incoming water (4) down through the filter and out the waste line (14). Opening valve "5" during backflush would contaminate the clean water line or prevent proper backwashing pressure. * **D) valves "4", "5", and "14":** This is incorrect because valve "5" (the filtered water outlet) must be **closed** during the backflush operation, as explained above.