Exam Question

### (a) Reasons for Purifier Overflow (6 Marks)
Overflow occurs when the oil-water interface within the purifier bowl is displaced too far towards the periphery, causing the separated oil to exit through the water outlet instead of the clean oil outlet. This is a critical failure of the hydraulic balance.
1. **Incorrect Gravity Disc (Oversized)**: The gravity disc is a fixed weir that controls the radius of the oil-water interface. An oversized disc (hole diameter too large) establishes the interface too close to the bowl periphery. This reduces the back pressure exerted by the water seal, allowing the lighter oil phase to easily displace the water and overflow.
2. **Loss or Insufficiency of Sealing Water**: The water seal is a fundamental requirement to create the dam against which oil builds up. If the initial charge of sealing water is insufficient, or if the seal is lost during operation (e.g., due to a leaking water supply solenoid valve or excessive vibration), there is no barrier to prevent the incoming oil from flowing directly out of the water port.