Question 25 OSE01 - Chief Engineer - OSV

The Correct Answer is C **Explanation for Option C (Worn blower rotor shaft bearings):** The presence of aluminum dust indicates severe mechanical wear and friction between moving parts, specifically the rotors and/or the rotors and the aluminum casing. In a Roots blower, the rotors are precision-machined to maintain extremely tight, non-contact clearances. These clearances are entirely dependent on the condition and alignment maintained by the **rotor shaft bearings**. If the bearings wear out (Option C), the rotor shafts lose their precise central positioning. This allows the meshing rotors to physically contact each other (rotor-to-rotor rubbing) or allows the rotor tips to rub against the aluminum casing walls (rotor-to-casing rubbing). This friction rapidly wears down the aluminum material, creating the aluminum dust observed in the air stream. This is the direct and most common cause of metallic particle generation inside a Roots blower. **Explanation of Incorrect Options:** * **A) Worn blower rotor shaft seals:** Seals are designed to prevent lubricating oil from entering the air stream or air pressure from escaping the casing. Wear on seals would primarily result in oil leakage into the air ducting, not the mechanical interference (rubbing) required to generate aluminum dust. * **B) Restricted scavenging air intake ports:** These ports are downstream of the blower, in the cylinder liner. Restriction would cause higher back pressure on the blower but would not mechanically alter the critical clearances or alignment of the blower rotors themselves. * **D) Restricted blower air intake filter:** A restricted filter, which is upstream of the blower, limits the volume of air entering the blower. This causes the blower to operate under higher vacuum/suction, leading to reduced airflow and potential overheating, but it does not directly cause the rotor shafts to shift out of alignment and rub, generating dust.