IN THIS GUIDE
After filter bags, cartridges or cleaning settings are changed, a baghouse may operate at a different system resistance. The direction and size of the change depend on the media, dust loading, cleaning cycle and duct arrangement. A baghouse fan retrofit review should begin with comparable before-and-after readings, not an assumption that the fan is automatically too small or too large.
Representative product image: C4-73 dust-collection centrifugal fan, shown as an equipment example rather than a baghouse retrofit case photo.
01. Record the filter and process change
Write down the old and new media type, dimensions, number of elements, filter area if known, cleaning method and any change to the inlet, outlet, hopper or ductwork. Record the process that creates the dust, its operating state and the time since the filter cleaning cycle. If the change included a new fan control set point or damper position, include that too.
02. Compare the same operating point
Use the plant's approved measurement points and units. Record baghouse differential pressure, fan inlet or outlet pressure where measured, airflow or a validated process indicator, fan speed or VFD setting, damper position, motor current or power and process load. Compare readings at similar production and cleaning conditions. A filter differential-pressure reading is not interchangeable with the fan's static or total pressure.
03. Check the system before changing the fan
- Confirm that pressure taps, gauges and airflow instruments are functioning and located as intended.
- Check for a blocked inlet, leaking access door, damaged duct joint, closed damper, obstructed screen or a changed branch connection.
- Review the filter cleaning sequence and verify that the new media and cleaning parameters match the approved design basis.
- Compare actual speed and damper settings with the fan curve and original commissioning point.
- Inspect inlet and outlet arrangements for new elbows, transitions or obstructions that could alter field performance.
Changes near the fan inlet or outlet can affect how the fan sees the system. Use the applicable fan curve and the installed system resistance together; do not use a free-air flow rating as the baghouse operating airflow.
04. Decide whether a retrofit is justified
Consider a fan, wheel or drive change only after the required process airflow, pressure basis and operating range have been verified. Check the selected operating point against the fan and motor limits and the project's control strategy. Any physical inspection or adjustment must follow the site's energy-isolation and permit procedures and be performed by authorized personnel.
05. Data to prepare for a supplier review
- Before-and-after filter specification and baghouse drawing.
- Process gas temperature, dust characteristics and operating cycle.
- Measured differential pressure, airflow, speed, damper and motor data with dates and conditions.
- Current fan curve, motor nameplate and drive/control information.
- Photos of the fan inlet, outlet, filter arrangement and any changed ductwork.
Frequently asked questions
Will new filter bags always increase pressure drop?
Not always. The result depends on the filter media, dimensions, loading, cleaning system and measurement conditions. Compare actual readings on the same basis.
Can I correct low airflow by opening the damper?
Do not make a change before checking the fan operating range, motor load and process requirements. A damper adjustment may move the operating point but will not repair a leak, blockage or unsuitable fan duty.
When should the fan be resized?
After confirming the required airflow and pressure at the updated system condition, and after evaluating the current fan curve, drive, motor and installation arrangement.
Related references
- Dust collection system airflow calculation
- How to read an industrial fan performance curve
- Static pressure vs. total pressure in industrial fans
- U.S. Department of Energy: Fan Systems
Planning a baghouse retrofit? Send the filter change record, fan curve and comparable field readings to sales@qiyuefan.com for a project-specific discussion.