Exam Question

A fuel oil purifier, typically a disc-stack centrifugal separator, is crucial for maintaining fuel quality by removing water, sludge, and other impurities. Proper operation is vital for engine longevity and performance. Deviations from normal operation can lead to various issues, as detailed below.
**(a) Reasons that may cause the purifier to overflow (6 marks)**
Purifier overflow indicates that the heavy phase (water and sludge) outlet is either blocked or the oil-water interface is incorrectly positioned, causing the oil (light phase) to exit via the heavy phase overflow outlet. The primary reasons include:
* **Incorrect Gravity Disc (Dam Ring) Size**: If the gravity disc fitted is too large for the specific gravity of the oil being purified, the oil-water interface will be pushed too far inwards towards the bowl axis. This allows the oil, instead of water, to exit through the heavy phase (water) outlet, leading to overflow.