Baghouse FAQ

A Magnehelic Gauge simply shows the difference between 2 pressures.

In most dust collectors, the low pressure side is connected to the clean side and the high pressure side is connected to the dirty side.

If connected to the inlet duct and outlet ducts of the baghouse, the reading might be higher by 1.5” or so

Most gauges read in inches of water:

water column or water gauge (“wc or “wg)

As the filterbags become coated the pressure drop increases. An increase in airflow due to increasing the fan speed or opening up additional ducts may also increase the gauge reading.

Ideally we are looking for a steady state of operation. This is where the airflow is maximized for the process, the efficiency of the filter media is at a maximum and the dust cake is not creating short term plugging.

The majority of dust collectors will operate in the 2 to 6” range on a gauge. Ideally we are looking for 2 to 4”.

Your particular system will have its own range.

Here are a few situations where we can use a Magnehelic to interpret a number of system conditions that could occur in a normally operating baghouse:

Please note: Check the gauge operation and lines 1st


Condition 1

Magnehelic Gauge

Possible Condition

Low airflow at the pick-ups

Reading is beyond the usual operating range

Plugged filters; cleaning system not operating correctly; full hopper; severely leaking dust discharge valve; fan damper open beyond usual position

 

 

 

Low airflow at the pick-ups

Reading is lower than the usual operating range

Exhaust fan damper is partially closed; fan belts are damaged and loose; outlet duct of the fan is plugged; duct runs are plugged; pulse cleaning system is leaking air severely; outside air entering in to the system between the clean side and outlet of the fan; fan inlet cone is damaged

 

 

 

Usual airflow at the pick-ups then flow drops off. Airflow returns to normal after the fan is shut off, bags cleaned then the fan is restarted again

Reading is normal then increases beyond the usual operating range. After cleaning the bags after the system shuts down, the reading returns to normal

This condition indicates an increase in airflow through the system. This is often damper related at the fan or in the main duct. It could also indicate a hole in the system before the dust collector.  The excess airflow is keeping product on the filters and will not allow it to clean off until the fan is shut-down and the filters cleaned down.

This is a commonly asked question and not an easy one to answer

In most manufacturing processes, in North America, 12 months is a generalized life expectancy.

In Europe, from conversations we have had with manufacturers and end-users, 2 years is considered to be average.

Asphalt Paving plant filters can last up to 7 seasons; woodworking filters can last from 12-months to 3 years.

Life expectancy of the filterbags is determined by many known and unknown factors:

  1. Design, style, model and sizing of the baghouse, fan, ducting, hooding and other components
  2. How often the system is used
  3. Dust loading in to the system
  4. Dust Particle size and population
  5. Physical condition of the baghouse
  6. Physical location of the system
  7. Process (gas stream) parameters (moisture, volatiles, corrosive elements)
  8. Maintenance of the system
  9. Ducting/hood design
  10. How often the bags are cleaned
  11. How often the baghouse is emptied
  12. Quality of the filter media and of the bag or cartridge construction
  13. Selection of the media…and the list goes on.

Each baghouse is unique. 2 identical baghouses on 2 identical processes may have different filter bag life results.

Each baghouse is unique. 2 identical baghouses on 2 identical processes may have different filter bag life results.

  1. Use a mid-range air to cloth ratio (5:1 on pulse jet systems; 3:1 on shaker systems for instance)
  2. Have a daily routine of visiting the system at least once per day and recording the Magnehelic or Photohelic reading
  3. Keep the hopper empty. Do not let it fill up
  4. Keep oil and water out of the system (housing leaks; condensation; process washing with the system running and no shut-offs on the pick-ups where washing is occurring; review leaking fire sprinklers)
  5. Have a yearly audit from an experienced baghouse service company. We offer monthly, quarterly; semi-annually and yearly inspections depending upon:
    1. The corporate need
    2. # of systems
    3. Dust product being collected
    4. Past experiences of the customer
  6. Inspect/service the exhaust fan and dust handling drives at least once per quarter
  7. Inspect the filter bag cleaning system once per quarter (minimum)
  8. Inspect the filters once per quarter

Perhaps the most important aspect of understanding bag life is that the filter bag is, in most instances, a retaining surface for a “dust filtering cake”.
Maintaining the dust cake at a steady state will help maintain the efficiency and life of the filter media.

Many industries use their own personnel to replace filter bags.

We see this particularly in the food industry where product or colour changes require frequent contamination control in the baghouse.

Generally, these systems are compact and can be serviced easily and quickly. We believe this makes total sense for the customer.

More complicated systems (not necessarily large), requiring a fast turnaround time and a skilled crew, are where we can fit in for you.

Customers generally agree that they need to keep focused on doing what they need to do manufacturing and process wise.

Our speciality and focus is baghouse maintenance.

In some instances, where it makes sense for both the customer and Frost, we will work hand-in- hand with their personnel to get the overhaul completed.

The minimum requirement is that you must meet the commitments of your Environmental Compliance Approval (ECA -Ministry of the Environment) agreement where your baghouse air/gas stream to the atmosphere.

To simplify this process, Due Diligence is the key phrase:

  1. Inspect your dust collector regularly (daily; monthly; quarterly; annually)
  2. Record the filter bag pressure drop readings daily where possible
  3. Record all maintenance activities for the system in a central log-book
  4. Service parts on the dust collector before they completely fail:
  5. a. Leaking bags
    b. Worn fan belts
    c. Hoppers filling up
    d. Filter bag cleaning systems
    e. Etc.
  6. Hire an outside company to:
  7. a. Provide an inspection program
    b. Help you set-up your own in-house inspection program
    c. Audit your program on a yearly basis

Running a system to failure is not considered good practice with baghouses.
There is a legal responsibility but it does not have to be complicated or expensive.

For systems where venting back into the building is permissible, the same process applies.

In the end, good dust collection at the process source, combined with lower than minimal system emissions, will be reflected by the quality of your Due Diligence Baghouse Program.