Exam Question
(a) Explain why a purifier is not attaining its rated speed on starting from rest? (8)
(b) How do you select the appropriate Gravity Disc of Purifier? Why is this selection an important element in the purifier operation? (8)
Class 4 (4th Engineer)
MEP
📅 Dec 2024
Reference Answer
### (a) Reasons a Purifier Fails to Attain its Rated Speed
A centrifugal purifier failing to reach its designed operational speed (typically 6,000-10,000 RPM) from a standstill is a critical issue indicating excessive opposing torque that the electric motor cannot overcome. A systematic investigation is required, focusing on mechanical, electrical, and operational factors.
**1. Mechanical Friction and Obstruction:**
* **Brake Remained Engaged:** The manually or automatically operated brake may not have fully disengaged. Continuous contact between the brake pads and the brake drum/bowl periphery creates a significant frictional drag, preventing acceleration. This also leads to rapid wear of the brake lining and can cause the motor to overheat due to sustained high current draw. *(Reference: Brake Pad Engagement)*
A centrifugal purifier failing to reach its designed operational speed (typically 6,000-10,000 RPM) from a standstill is a critical issue indicating excessive opposing torque that the electric motor cannot overcome. A systematic investigation is required, focusing on mechanical, electrical, and operational factors.
**1. Mechanical Friction and Obstruction:**
* **Brake Remained Engaged:** The manually or automatically operated brake may not have fully disengaged. Continuous contact between the brake pads and the brake drum/bowl periphery creates a significant frictional drag, preventing acceleration. This also leads to rapid wear of the brake lining and can cause the motor to overheat due to sustained high current draw. *(Reference: Brake Pad Engagement)*
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