Exam Question

### (a) Reasons for a Purifier to Overflow
An overflow condition in a purifier occurs when the liquid (oil) being purified is discharged through the heavy phase (water) outlet instead of the light phase (clean oil) outlet. This indicates a failure in establishing or maintaining the correct liquid interface within the bowl. The primary reasons are as follows:
1. **Insufficient or No Sealing Water**: The sealing water creates a liquid seal or dam at the periphery of the bowl, preventing the oil from exiting through the water outlet. If this water is not supplied, supplied at low pressure, or in insufficient quantity upon startup or after a desludge, the seal will not form, and the incoming oil will immediately flow out of the water port. `(Sourced from: Sealing water low)`
2. **Excessive Back Pressure**: The clean oil outlet line has a designed operating pressure, usually regulated by a valve. If this back pressure is too high due to a downstream blockage or an incorrectly adjusted valve, it impedes the discharge of clean oil. This causes the oil level inside the bowl to rise above the gravity disc (dam ring), forcing it to exit through the water outlet. `(Sourced from: Excessive back pressure)`