Non-perforated basket centrifuge – principle, construction, working, uses, merits, demerits MCQs With Answer

Introduction

The non-perforated basket centrifuge is a key solid-liquid separation device in pharmaceutical processing, used for settling and retaining solids inside a closed drum while clarified liquid overflows or is removed. This overview explains the principle, construction, working, uses, merits and demerits in simple terms for B.Pharm students. Covered topics include centrifugal sedimentation, basket and casing design, drive systems, batch operation, cake washing and drying, and common pharmaceutical applications such as API isolation and crystallization. Emphasis is placed on operational parameters, maintenance and troubleshooting to help optimize separation performance in labs and production. ‘Now let’s test your knowledge with 50 MCQs on this topic.’

Q1. What is the primary separation principle of a non-perforated basket centrifuge?

• Gravitational settling
• Centrifugal sedimentation
• Membrane filtration
• Evaporation

Correct Answer: Centrifugal sedimentation

Q2. Which component forms the rotating containment for solids in a non-perforated basket centrifuge?

• Perforated drum
• Non-perforated basket
• Scroll conveyor
• Slip ring assembly

Correct Answer: Non-perforated basket

Q3. How is clarified liquid typically removed in a non-perforated basket centrifuge?

• Through perforations in the basket wall
• By overflow or decanting from the casing
• By a scroll conveyor
• By vacuum filtration

Correct Answer: By overflow or decanting from the casing

Q4. Which pharmaceutical operation commonly uses non-perforated basket centrifuges?

• Sterile filling
• API crystallization and cake washing
• Tablet compression
• Granulation drying

Correct Answer: API crystallization and cake washing

Q5. One advantage of a non-perforated basket over a perforated basket is:

• Faster continuous discharge
• Lower risk of particle loss through holes
• Higher throughput for very fine suspensions
• Built-in scroll for continuous cake removal

Correct Answer: Lower risk of particle loss through holes

Q6. Which parameter directly increases the centrifugal force acting on particles?

• Decreasing rotor radius
• Increasing rotational speed (rpm)
• Lowering temperature
• Increasing ambient pressure

Correct Answer: Increasing rotational speed (rpm)

Q7. The relative centrifugal force (RCF) is proportional to which of these?

• rpm only
• radius only
• rpm squared multiplied by radius
• temperature divided by rpm

Correct Answer: rpm squared multiplied by radius

Q8. Which maintenance activity is particularly important for non-perforated basket centrifuges handling corrosive solvents?

• Balancing of the rotor
• Regular painting of external panels
• Periodically replacing the drive motor
• Cleaning and corrosion inspection of the basket and casing

Correct Answer: Cleaning and corrosion inspection of the basket and casing

Q9. Non-perforated basket centrifuges are typically operated in which mode for pharmaceutical batch work?

• Continuous mode with scroll discharge
• Batch (intermittent) mode
• Vacuum continuous filtration mode
• Membrane crossflow mode

Correct Answer: Batch (intermittent) mode

Q10. Which part provides the driving torque to the rotating basket?

• Fluid inlet nozzle
• Electric motor and drive assembly
• Perforated sieve
• Discharge valve

Correct Answer: Electric motor and drive assembly

Q11. What happens to the solid particles inside a non-perforated basket during spinning?

• They dissolve in the liquid
• They migrate outward and form a cake on the inner surface
• They evaporate
• They are transported out by a screw conveyor

Correct Answer: They migrate outward and form a cake on the inner surface

Q12. Why might a non-perforated basket be preferred for sticky or fibrous solids?

• It has larger perforations
• It prevents clogging of holes and allows easy cake retention
• It provides continuous screw discharge
• It uses membrane filtration to remove liquids

Correct Answer: It prevents clogging of holes and allows easy cake retention

Q13. Which variable is critical to control to avoid excessive cake compaction and product damage?

• Rotor acceleration and final rpm
• Ambient humidity only
• Color of the basket
• Operator shoe size

Correct Answer: Rotor acceleration and final rpm

Q14. A common method for washing the cake in a non-perforated basket centrifuge is:

• Spraying wash solvent onto the cake while spinning
• Applying vacuum to the cake through perforations
• Heating the cake with infrared lamps
• Removing the cake and immersing it in wash solvent externally

Correct Answer: Spraying wash solvent onto the cake while spinning

Q15. Which is a key disadvantage of non-perforated basket centrifuges in large-scale production?

• They always operate continuously
• Batch stopping for cake discharge reduces throughput
• They do not retain solids
• They cannot be cleaned

Correct Answer: Batch stopping for cake discharge reduces throughput

Q16. What is the role of a casing in a non-perforated basket centrifuge?

• To act as a perforated filter
• To collect expelled liquid and provide containment
• To heat the sample
• To automatically remove cake

Correct Answer: To collect expelled liquid and provide containment

Q17. Which safety device is commonly included on centrifuges to protect against imbalance?

• Imbalance detection and automatic shut-off
• Perforated basket guard
• Thermal fuse for the motor coils only
• Manual balance weight

Correct Answer: Imbalance detection and automatic shut-off

Q18. In which scenario is non-perforated basket centrifuge less effective?

• When handling coarse crystals
• When separating suspensions with very fine colloidal particles
• When washing thick cake
• When handling viscous slurries with large solids

Correct Answer: When separating suspensions with very fine colloidal particles

Q19. What is one method to improve liquid clarification in a non-perforated basket centrifuge?

• Decrease rotational speed
• Add flocculant to agglomerate fine particles
• Remove the basket entirely
• Reduce the rotor radius to zero

Correct Answer: Add flocculant to agglomerate fine particles

Q20. Which material property of the product influences selection of basket material/coating?

• Color preference of operators
• Chemical compatibility and corrosion resistance
• Shape of the production facility
• Country of manufacture

Correct Answer: Chemical compatibility and corrosion resistance

Q21. How is the cake typically discharged from a non-perforated basket?

• Through continuous screw ejection
• By stopping rotation and manually removing the cake
• By vacuum suction through perforations
• By melting the cake with heat

Correct Answer: By stopping rotation and manually removing the cake

Q22. Which design feature reduces solvent carryover in the clarified liquid?

• Perforated basket walls
• Splash rings and weirs in the casing
• Open-top baskets without casing
• Absence of a motor

Correct Answer: Splash rings and weirs in the casing

Q23. Which cleaning method is commonly used for pharmaceutical non-perforated baskets?

• CIP (clean-in-place) or manual cleaning with compatible solvents
• Never cleaning to maintain sterility
• Only ultrasonic waves without solvents
• Immersion in molten metal

Correct Answer: CIP (clean-in-place) or manual cleaning with compatible solvents

Q24. Non-perforated basket centrifuges are best for retaining particles of what nature?

• Extremely colloidal, truly solute-sized particles
• Coarse to medium-sized particles that form a cake
• Gaseous bubbles only
• Completely dissolved molecules

Correct Answer: Coarse to medium-sized particles that form a cake

Q25. Which operational step immediately follows feeding the slurry into the centrifuge in batch mode?

• Immediate cake discharge
• Acceleration to design rpm to form the cake
• Permanent sealing of the machine
• Cooling the slurry to freezing

Correct Answer: Acceleration to design rpm to form the cake

Q26. Which factor influences the thickness and density of the cake formed?

• Rotor color
• Feed solids concentration and centrifugation time
• Day of the week
• Ambient music

Correct Answer: Feed solids concentration and centrifugation time

Q27. Which of the following is a merit of non-perforated basket centrifuges in pharma labs?

• They guarantee continuous large-scale production without interruption
• They are simple to operate and suitable for delicate cake handling
• They eliminate the need for solvent handling
• They are ideal for separating gaseous mixtures

Correct Answer: They are simple to operate and suitable for delicate cake handling

Q28. Which problem indicates an overloaded centrifuge?

• Excessively thin cake with very little solids
• High vibration and frequent imbalance alarms
• Perfectly clear effluent always
• Lower-than-average motor temperature

Correct Answer: High vibration and frequent imbalance alarms

Q29. Why is controlling feed rate important in non-perforated basket centrifuges?

• To keep the machine in continuous production mode
• To ensure proper cake formation and avoid splashing or overload
• To change the color of the cake
• To reduce motor electricity consumption to zero

Correct Answer: To ensure proper cake formation and avoid splashing or overload

Q30. Which inspection is critical after repeated batch runs with solvent exposure?

• Checking the paint gloss only
• Inspecting seals, bearings and basket for solvent damage
• Replacing the motor each time
• Removing all safety guards permanently

Correct Answer: Inspecting seals, bearings and basket for solvent damage

Q31. How does adding a flocculant affect centrifugation?

• It decreases particle size and hinders settling
• It promotes agglomeration and enhances settling rate
• It dissolves solids completely
• It always corrodes the basket

Correct Answer: It promotes agglomeration and enhances settling rate

Q32. What operational change can reduce solvent entrainment in the cake?

• Shortening centrifugation time
• Increasing spin time at moderate rpm for better drainage
• Removing the casing
• Using a lower density solvent only

Correct Answer: Increasing spin time at moderate rpm for better drainage

Q33. In comparison to perforated centrifuges, non-perforated types typically:

• Allow continuous cake discharge with no stoppages
• Retain cake internally for batch removal and are less prone to clogging
• Always provide better clarification for colloids
• Require perforations to work

Correct Answer: Retain cake internally for batch removal and are less prone to clogging

Q34. Which test parameter is commonly recorded to evaluate centrifuge performance?

• Color of the basket
• Clarity of effluent (turbidity or % transmission)
• Number of operators present
• Ambient scent

Correct Answer: Clarity of effluent (turbidity or % transmission)

Q35. Which operational practice minimizes solvent exposure risk to operators?

• Operating at higher rpm than rated
• Using proper containment, sealed lids, and local exhaust ventilation
• Removing guards before operation
• Never wearing PPE

Correct Answer: Using proper containment, sealed lids, and local exhaust ventilation

Q36. Which material is commonly used to fabricate baskets for solvent-resistant operation?

• Low-grade painted steel only
• Stainless steel (e.g., SS316) or suitably coated alloys
• Cardboard
• Pure wood

Correct Answer: Stainless steel (e.g., SS316) or suitably coated alloys

Q37. The presence of significant fines in feed slurry will generally require:

• Lower centrifugal force and no pre-treatment
• Pre-treatment such as flocculation or filter-aid addition
• Ignoring the fines completely
• Immediate discharge without spinning

Correct Answer: Pre-treatment such as flocculation or filter-aid addition

Q38. Which of the following is a demerit specifically related to product handling in non-perforated basket centrifuges?

• Difficulty in recovering cake without exposure or contamination during manual removal
• They always produce sterile cake
• They make cakes that are self-disintegrating into liquid
• They eliminate the need for downstream drying

Correct Answer: Difficulty in recovering cake without exposure or contamination during manual removal

Q39. What effect does increasing the feed solids concentration have, all else equal?

• Decreases cake thickness
• Increases cake thickness and possibly solidity
• Has no effect on cake formation
• Makes the centrifuge convert to a perforated type

Correct Answer: Increases cake thickness and possibly solidity

Q40. What operational control helps protect bearings from solvent ingress?

• Using open bearings with no seals
• Proper sealing, labyrinth seals or protective covers
• Increasing rpm to maximum
• Removing lubrication entirely

Correct Answer: Proper sealing, labyrinth seals or protective covers

Q41. In troubleshooting poor clarity of effluent, which is a likely cause?

• Low feed solids concentration
• Insufficient centrifugal force or presence of many fines
• Excessive vacuum in the casing
• Over-application of polish coat on the basket

Correct Answer: Insufficient centrifugal force or presence of many fines

Q42. What is a common use of cake washing in pharmaceutical centrifugation?

• To color the cake
• To remove mother liquor and impurities from crystals/APIs
• To make cake more fluid for discharge only
• To inflate the cake for better packaging

Correct Answer: To remove mother liquor and impurities from crystals/APIs

Q43. Which design choice helps minimize vibration during operation?

• Operating with an unbalanced basket intentionally
• Precision balancing of rotor and periodic dynamic balancing
• Using the heaviest possible basket regardless of balance
• Removing the motor mount

Correct Answer: Precision balancing of rotor and periodic dynamic balancing

Q44. A typical sign that cake is still wet after spinning is:

• Very low residual solvent in the cake
• High solvent retention in the cake and slow drip after stopping
• Solid cake falling apart instantly
• Cake being completely dry and powdery

Correct Answer: High solvent retention in the cake and slow drip after stopping

Q45. What is one method to improve drying of the cake in the basket?

• Reduce spin speed to zero immediately
• Extend spin/drain time or increase rpm for final drainage phase
• Never wash the cake
• Immerse the basket in liquid nitrogen during spin

Correct Answer: Extend spin/drain time or increase rpm for final drainage phase

Q46. Which of the following is a direct consequence of operating above rated rpm?

• Improved safety
• Excessive stresses on basket and possible mechanical failure
• Instant purification of solvent
• Automatic reduction in feed solids

Correct Answer: Excessive stresses on basket and possible mechanical failure

Q47. Which monitoring parameter helps detect early bearing failure?

• Effluent color only
• Vibration analysis and bearing temperature monitoring
• Operator mood
• Ambient room humidity alone

Correct Answer: Vibration analysis and bearing temperature monitoring

Q48. For solvent-sensitive APIs, which practice improves product safety during centrifugation?

• Open-basket manual discharge without containment
• Using closed systems, inert atmosphere and solvent recovery tools
• Exposing the cake to ambient oxygen for long times
• Mixing the cake with random reagents

Correct Answer: Using closed systems, inert atmosphere and solvent recovery tools

Q49. Which downstream step often follows centrifugation of API crystals?

• Immediate tablet compression without drying
• Drying (tray or vacuum drying) and milling as needed
• Discarding the cake as waste always
• Direct dissolution back into mother liquor

Correct Answer: Drying (tray or vacuum drying) and milling as needed

Q50. Why is documentation of centrifuge operating parameters important in pharma production?

• It allows random changes without traceability
• It ensures reproducibility, quality control and regulatory compliance
• It enables ignoring validation requirements
• It replaces the need for SOPs

Correct Answer: It ensures reproducibility, quality control and regulatory compliance