NCT System Maintenance & Troubleshooting 3 — Questions and Answers
Question 1: A filter housing gasket is found to be compressed and deformed during inspection. What is the primary risk if the gasket is not replaced?
- Increased energy efficiency
- Air bypass around the filter, reducing filtration effectiveness (Correct answer)
- Higher filter loading rate
- Reduced fan motor speed
Correct answer: Air bypass around the filter, reducing filtration effectiveness
A deformed gasket cannot create an airtight seal, allowing unfiltered air to bypass the filter media and enter the downstream system.
Question 2: Which tool is most appropriate for field-testing HEPA filter integrity after installation?
- Vane anemometer
- Aerosol photometer with challenge aerosol (Correct answer)
- Sling psychrometer
- Pitot tube manometer
Correct answer: Aerosol photometer with challenge aerosol
An aerosol photometer used with a challenge aerosol (such as DOP or PAO) is the standard instrument for scanning and verifying HEPA filter integrity.
Question 3: A technician observes that pre-filters are loading much faster than expected. What operational change would most effectively extend pre-filter service life?
- Remove pre-filters to reduce pressure drop
- Increase fan speed to push contaminants through faster
- Investigate and control the upstream dust source (Correct answer)
- Switch to a lower-efficiency pre-filter
Correct answer: Investigate and control the upstream dust source
Addressing the upstream dust source reduces the contaminant burden on pre-filters, directly extending their service life.
Question 4: During a maintenance shutdown, a technician finds the final filter frame bent and warped. What is the recommended course of action?
- Straighten the frame with pliers and reinstall
- Install the filter and monitor differential pressure
- Replace the filter with a new unit to ensure proper seating (Correct answer)
- Add extra caulk around the edges to compensate
Correct answer: Replace the filter with a new unit to ensure proper seating
A bent or warped frame prevents uniform seating against the housing, creating potential bypass pathways that compromise filtration.
Question 5: What is the significance of recording filter differential pressure readings at consistent airflow conditions during each maintenance visit?
- It satisfies OSHA personal protective equipment requirements
- It enables accurate comparison of filter loading between visits (Correct answer)
- It determines the filter manufacturer's warranty status
- It calculates duct insulation R-value
Correct answer: It enables accurate comparison of filter loading between visits
Consistent airflow conditions ensure differential pressure readings are comparable between visits, allowing accurate tracking of filter loading trends.
Question 6: A pulse-jet cleaned cartridge filter fails to clean properly and differential pressure keeps rising. What component is most likely malfunctioning?
- Filter media fiber diameter
- Pulse valve or compressed air supply to the cleaning system (Correct answer)
- Downstream HEPA filter
- Duct insulation wrap
Correct answer: Pulse valve or compressed air supply to the cleaning system
Pulse-jet cleaning depends on properly functioning pulse valves and adequate compressed air supply; failure of either prevents effective cake removal.
Question 7: Which condition indicates that a V-bank filter configuration is operating at or near its end-of-life?
- Differential pressure has reached the manufacturer's final resistance rating (Correct answer)
- Filter color has changed from white to gray
- Inlet duct temperature has increased
- The building occupancy has increased
Correct answer: Differential pressure has reached the manufacturer's final resistance rating
Reaching the manufacturer's specified final resistance rating indicates the filter has loaded to its designed capacity and must be replaced.
NCT System Maintenance & Troubleshooting 3
A filter housing gasket is found to be compressed and deformed during inspection.
What is the primary risk if the gasket is not replaced?