Introduction: A bag filter (baghouse) is a key particulate removal device in pharmaceutical manufacturing, combining simple construction with effective dust collection. Understanding the bag filter principle, construction, working, uses, merits and demerits is essential for B. Pharm students involved in process engineering, quality assurance and GMP compliance. Topics include filter media types (polyester, PTFE, polypropylene), filtration mechanisms (mechanical capture, cake filtration), cleaning methods (pulse-jet, reverse-air, shaker), performance metrics (filtration efficiency, pressure drop) and maintenance/validation considerations. This guide prepares you for theoretical and practical aspects and helps improve contamination control strategies. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary working principle of a bag filter?
- Absorption of gases by the bag material
- Electrostatic attraction of particles
- Mechanical filtration by retaining particles on the bag surface and within the media
- Chemical neutralization of particulate matter
Correct Answer: Mechanical filtration by retaining particles on the bag surface and within the media
Q2. Which component holds the filter bag in correct shape and prevents collapse?
- Inlet duct
- Bag cage or support cage
- Hopper
- Outlet stack
Correct Answer: Bag cage or support cage
Q3. Which filtration mechanism dominates for very small particles (<0.1 µm)?
- Sieving
- Inertial impaction
- Diffusion (Brownian motion)
- Gravitational settling
Correct Answer: Diffusion (Brownian motion)
Q4. In a pulse-jet baghouse, how is the cleaning achieved?
- By mechanically shaking the bags
- By reversing the gas flow periodically
- By a short, high-pressure pulse of compressed air into the bag
- By heating the bags to burn off dust
Correct Answer: By a short, high-pressure pulse of compressed air into the bag
Q5. Which bag material is commonly used for chemically aggressive environments and high temperature resistance?
- Polyester
- Polypropylene
- PTFE (Teflon)
- Cotton
Correct Answer: PTFE (Teflon)
Q6. What is the effect of cake formation on filtration efficiency?
- It reduces filtration efficiency
- It increases filtration efficiency up to an optimum thickness
- It has no effect on efficiency
- It always causes clogging immediately
Correct Answer: It increases filtration efficiency up to an optimum thickness
Q7. Which parameter is most directly used to indicate bag filter performance during operation?
- Pressure drop across the bag filter
- Ambient room temperature
- Color of the bag material
- Height of the stack
Correct Answer: Pressure drop across the bag filter
Q8. Select a common disadvantage of bag filters in pharmaceutical applications.
- Excellent capture of ultrafine particles
- Potential for fiber shedding and contamination
- Zero maintenance requirement
- Complete removal of gaseous vapors
Correct Answer: Potential for fiber shedding and contamination
Q9. Which cleaning method is most suitable for continuous operation with minimal downtime?
- Manual shaking during shutdown
- Pulse-jet cleaning during operation
- Manual replacement of bags each hour
- Burning accumulated dust
Correct Answer: Pulse-jet cleaning during operation
Q10. What is the role of the hopper in a bag filter system?
- To house the bag cages
- To collect and funnel the removed dust/dust cake for disposal
- To compress the bags
- To introduce compressed air pulses
Correct Answer: To collect and funnel the removed dust/dust cake for disposal
Q11. Which of the following best describes the direction of gas flow in a typical baghouse?
- Counter-current with respect to bag orientation
- From inside-to-outside of the bag or outside-to-inside depending on design
- Only upward through the bags
- Gas flow direction is irrelevant
Correct Answer: From inside-to-outside of the bag or outside-to-inside depending on design
Q12. What is the common cause of a sudden rise in pressure drop across the bag filter?
- Improved filtration efficiency
- Bag rupture or severe clogging
- Decrease in dust load
- Cleaning cycle initiation
Correct Answer: Bag rupture or severe clogging
Q13. Which particle capture mechanism is dominant for particles around 1–10 µm?
- Electrostatic charging only
- Interception and inertial impaction
- Diffusion predominately
- Gravitational deposition only
Correct Answer: Interception and inertial impaction
Q14. For GMP compliance in pharmaceuticals, which concern is most relevant when selecting bag filter media?
- Color of the bag only
- Potential for extractables/leachables and fiber shedding
- Electrical conductivity
- Magnetic properties
Correct Answer: Potential for extractables/leachables and fiber shedding
Q15. Which maintenance activity helps extend bag life and maintain efficiency?
- Ignoring irregular pressure drops
- Regular inspection, timely replacement, and proper cleaning cycles
- Using higher compressed air pressure than recommended
- Sealing the inlet permanently
Correct Answer: Regular inspection, timely replacement, and proper cleaning cycles
Q16. Which of the following is a primary merit of bag filters?
- Extremely high capital cost compared to all filters
- Ability to achieve high particulate removal efficiency at various particle sizes
- Incineration capability
- Inability to capture fine particles
Correct Answer: Ability to achieve high particulate removal efficiency at various particle sizes
Q17. Which cleaning mechanism uses a slight reversal of flow for bag cleaning?
- Pulse-jet cleaning
- Reverse-air cleaning
- Mechanical shaking
- Chemical washing in situ
Correct Answer: Reverse-air cleaning
Q18. Which design parameter influences residence time and cake formation in a bag filter?
- Fabric color
- Gas flow velocity and face velocity
- Type of paint on housing
- Position of external lights
Correct Answer: Gas flow velocity and face velocity
Q19. Which of the following is an indication that pulse-jet valves or the compressor may be failing?
- Decreased ambient humidity
- Insufficient cleaning resulting in steadily increasing pressure drop between pulses
- Improved filter efficiency
- Stable pressure drop during operation
Correct Answer: Insufficient cleaning resulting in steadily increasing pressure drop between pulses
Q20. Bag filters are generally not suitable for removing which contaminant from gas streams?
- Fine solid particulates
- High concentration vapors and gases (without sorbents)
- Fibrous dust
- Coarse dust
Correct Answer: High concentration vapors and gases (without sorbents)
Q21. Which test is important for qualification of a bag filter system in sterile manufacturing areas?
- Vacuum integrity test
- Particle count and leak integrity testing and validation
- Color fastness test
- Thermal conductivity test
Correct Answer: Particle count and leak integrity testing and validation
Q22. What does ‘face velocity’ refer to in bag filter design?
- Velocity of air through the inlet duct only
- Velocity of gas approaching the face area of the filter media (m/s)
- Velocity of dust falling into the hopper
- Velocity of cleaning pulse
Correct Answer: Velocity of gas approaching the face area of the filter media (m/s)
Q23. Which property of bag material is most critical when filtering oily aerosols?
- Thermal expansion coefficient
- Oleophobicity and resistance to blinding
- Magnetism
- Color retention
Correct Answer: Oleophobicity and resistance to blinding
Q24. In a bag filter, ‘cake release’ refers to:
- The formation of the first dust layer
- The detachment of accumulated dust from the bag during cleaning
- The emission of gases from the hopper
- Corrosion of the bag cage
Correct Answer: The detachment of accumulated dust from the bag during cleaning
Q25. Which filtration efficiency is typically expected for a well-operated bag filter on particulate matter >1 µm?
- Below 10%
- Around 30–50%
- Greater than 99%
- Exactly 75%
Correct Answer: Greater than 99%
Q26. What is a common reason for uneven bag wear leading to premature failure?
- Uniform dust distribution
- Poor gas distribution and uneven inlet flow
- Ideal cleaning cycle
- Using a bag cage of correct size
Correct Answer: Poor gas distribution and uneven inlet flow
Q27. Which bag filter configuration is suitable for intermittent processes with variable dust loads?
- Single large baghouse with no sectional isolation
- Modular baghouse with compartmentalization and isolation valves
- Open-air settling only
- Fixed single-chamber system with no access doors
Correct Answer: Modular baghouse with compartmentalization and isolation valves
Q28. Which measurement helps determine when a bag requires replacement?
- Color matching against a chart
- Measured increase in pressure drop beyond recommended limit and physical inspection
- Time elapsed only
- Bag diameter alone
Correct Answer: Measured increase in pressure drop beyond recommended limit and physical inspection
Q29. Which of the following reduces blinding of filter bags by sticky dusts?
- Using a more hydrophilic fabric
- Using surface-treated, PTFE-coated or oleophobic media
- Increasing system temperature drastically
- Removing the cleaning system
Correct Answer: Using surface-treated, PTFE-coated or oleophobic media
Q30. In bag filter operation, what is meant by ‘cleaning frequency’?
- The hourly replacement of bag material
- The interval at which cleaning pulses or cycles are applied
- The frequency of sound produced by the fan
- The ambient noise level in the plant
Correct Answer: The interval at which cleaning pulses or cycles are applied
Q31. Which of the following is a major demerit of bag filters regarding occupational safety?
- They eliminate all airborne particles
- Risk of dust release during bag change and maintenance, causing exposure
- They sterilize the air
- They reduce workplace noise
Correct Answer: Risk of dust release during bag change and maintenance, causing exposure
Q32. What is the typical role of an inlet baffle in a bag filter?
- To increase particle velocity
- To promote even gas distribution and reduce inlet turbulence
- To heat the incoming stream
- To compress the dust cake
Correct Answer: To promote even gas distribution and reduce inlet turbulence
Q33. Which of the following is most likely to damage filter bags?
- Operating within recommended temperature limits
- Abrasive dust with sharp particles and high velocity
- Proper pulsing pressure
- Appropriate cage design
Correct Answer: Abrasive dust with sharp particles and high velocity
Q34. What action is recommended to prevent cross-contamination when changing bags in a pharmaceutical plant?
- Changing bags in open area without containment
- Use of containment enclosures, vacuum transfers, and appropriate PPE
- Shaking bags vigorously outdoors
- Rinsing bags in production area
Correct Answer: Use of containment enclosures, vacuum transfers, and appropriate PPE
Q35. Which factor does NOT directly affect the filtration efficiency of a bag filter?
- Media pore size and structure
- Particle size distribution of the dust
- Operator’s handwriting
- Face velocity
Correct Answer: Operator’s handwriting
Q36. For control of airborne pharmaceutical powder during transfer, which bag filter feature is most valuable?
- High thermal conductivity
- Low capture efficiency
- High filtration efficiency and compatibility with containment systems
- Large physical size only
Correct Answer: High filtration efficiency and compatibility with containment systems
Q37. Which bag cleaning approach is gentlest on bags but slower and requires offline cleaning?
- Pulse-jet cleaning
- Reverse-air cleaning or mechanical shaker which require offline or sectional isolation
- High-pressure steam cleaning during operation
- Explosive dust burnoff
Correct Answer: Reverse-air cleaning or mechanical shaker which require offline or sectional isolation
Q38. What is the likely consequence of operating a bag filter at excessively high face velocity?
- Improved bag life
- Increased re-entrainment of particles and higher pressure drop, reduced efficiency
- Reduced gas flow through the system
- Lower dust loading on bags
Correct Answer: Increased re-entrainment of particles and higher pressure drop, reduced efficiency
Q39. Which inspection during routine maintenance helps detect early bag failure?
- Visual inspection for tears, holes, and wear; bag leak detector testing
- Smell test at the outlet
- Measuring bag length only
- Counting the number of bags weekly without inspection
Correct Answer: Visual inspection for tears, holes, and wear; bag leak detector testing
Q40. In pharmaceutical environments, why might PTFE-coated bags be preferred?
- They are cheaper than all alternatives
- They provide chemical resistance, low particle release and easy cake release
- They absorb moisture to prevent clumping
- They dissolve in solvents for easy cleaning
Correct Answer: They provide chemical resistance, low particle release and easy cake release
Q41. Which measurement technique can be used to monitor baghouse emissions compliance?
- Particle counting at stack outlet and opacity monitoring
- Only listening to the fan noise
- Measuring bag color changes
- Counting the number of cleaning pulses
Correct Answer: Particle counting at stack outlet and opacity monitoring
Q42. What is the purpose of pulse control sequencing in a multi-row pulse-jet baghouse?
- To pulse all bags simultaneously for maximum stress
- To stagger pulses across compartments for stable operation and minimal process disturbance
- To increase the temperature in the hopper
- To disable cleaning entirely
Correct Answer: To stagger pulses across compartments for stable operation and minimal process disturbance
Q43. Which safety concern is most critical when handling explosive dusts with bag filters?
- Ensuring adequate spark control, grounding, and explosion venting or suppression
- Using combustible materials in the beds
- Operating at very low humidity intentionally
- Removing baghouse grounding to reduce electrical costs
Correct Answer: Ensuring adequate spark control, grounding, and explosion venting or suppression
Q44. Which characteristic of dust increases the tendency to blind or cake the filter bag rapidly?
- Dry, free-flowing, non-cohesive dust
- Sticky, oily or hygroscopic dust
- Very coarse inert dust only
- Dust with no organic content
Correct Answer: Sticky, oily or hygroscopic dust
Q45. For particle size distribution dominated by submicron particles, which additional control might be needed along with a bag filter?
- Nothing else is ever needed
- Upstream cyclones only
- Combination with electrostatic precipitators or HEPA downstream filtration
- Removing the bags periodically
Correct Answer: Combination with electrostatic precipitators or HEPA downstream filtration
Q46. What does the term ‘cake density’ influence in bag filter design?
- The color of the cake
- The pressure drop, cleaning energy required and hopper discharge behavior
- The electrical resistance of bags
- The geographic location of the plant
Correct Answer: The pressure drop, cleaning energy required and hopper discharge behavior
Q47. Which operational parameter is adjusted to improve cake release during pulse-jet cleaning?
- Compressed air pulse pressure, pulse duration and sequencing
- Bag color
- Number of support cages
- Number of inlet ducts
Correct Answer: Compressed air pulse pressure, pulse duration and sequencing
Q48. Which bag filter design is preferred when minimizing contamination risk during bag change is critical?
- Open-top bags changed manually without containment
- Bag-in/bag-out or contained change-out systems
- Bags stitched in place permanently
- Replacing the entire housing daily
Correct Answer: Bag-in/bag-out or contained change-out systems
Q49. Which factor influences chemical compatibility of bag media in pharmaceutical solvent-laden dust streams?
- Bag weave pattern only
- Chemical resistance of the polymer and presence of coatings like PTFE
- The bag color palette
- Ambient sound levels
Correct Answer: Chemical resistance of the polymer and presence of coatings like PTFE
Q50. During validation of a bag filter for production, which documentation is essential?
- Only the invoice for the bags
- Design specifications, FAT/SAT records, cleaning validation, maintenance logs, and performance test reports
- Only photographs of the bags
- Only a verbal statement from the operator
Correct Answer: Design specifications, FAT/SAT records, cleaning validation, maintenance logs, and performance test reports
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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