All dust collectors include a hopper that collects the captured dust.  These hoppers are not designed for storage of the dust, however.  They are there for the dust to collect until it passes out of the dust collector through an airlock, such as a rotary valve, double-dump valve, trickle valve, etc.  Adequate discharge intervals are important.   If enough dust builds up in the hopper, then the dust will get re-entrained into the air.  This could cause a few issues. 

Baghouse filters are great for dust collection; however, if they develop a hole, then there is a clear path for the dust to take through the filter.  Over time, the hole will increase in size, allowing more and more dust through.  Filters with holes decrease the removal efficiency of the dust collection system and could violate your air permit.

The filters in a baghouse are the primary dust collecting component.  The filters build up an initial layer of dust, preventing dust from penetrating the filter while allowing air to pass through.  As the dust layer increases in thickness, it is harder for air to pass through.  This is measured by an increasing pressure drop.  Since most dust collection systems don’t use Variable Frequency Drives (VFDs) and airflow transmitters to control the airflow, the airflow through the system will decrease as the pressure drop across the bags increases.  Most baghouses use compressed air blown down the bag, to expand the bag off its cage to jar the most recent layers of dust off the filter. Other baghouses use a shaking cycle to remove the top layer of dust.

Over time, the constant expanding and contracting of the bag during the cleaning process could cause a hole to develop in the bag.  There are a few different ways for the bag filter to develop holes:

1. Gradual expansion of natural gaps in the filter during the cleaning process.
2. The bag being caught and ripped on the metal cage during the cleaning process.
3. High temperature causing localized failure of the filter.
4. Abrasive dust gradually wearing out filter materials.
5. High velocity of the air gradually wearing out the filters.

There are bag break sensors available on the market that will let you know when they detect a bag break.  Often, this is done by measuring the amount of dust particles after the baghouse and when the concentration suddenly jumps, an alarm is set.  Certain baghouse controllers will measure the compressed air used during the cleaning process.  From this, they can tell which row of bags have a hole so you can replace only a row of bags instead of all the bags in the baghouse.

A yearly maintenance inspection of the baghouse will help you avoid operational issues that could develop throughout the year.  This can prevent you from getting a fine or having to shut down the system in an emergency.

Find out more. 

When selecting the airlock for your dust collector, it is important to think about air leakage.  A little air leakage through the airlock isn’t a usually a big deal with many baghouse applications, but air leakage can cause major issues with some applications.  So it is important that you identify if your system will have issues with air leakage and then select the proper airlock valve.

Some dust collection system issues that could come with air leakage include:

1. Decrease airflow at pickup points – If an airlock leaks too much air into a system, it could decrease the airflow at the pickup point, thereby causing less dust to be collected.
2. Blowing dust out of the airlock – If too much air leaks out of the system through the airlock, the collected dust might be blown out of the airlock, causing the collected dust scatter on the ground around the dust collector.
3. Dust that reacts with water – Humidity from outside the process can cause dust to become sticky, bridge, or even explosive in special circumstances.
4. Systems that are oxygen deficient for reaction or explosive prevention – Outside air can introduce oxygen to the system which could feed a reaction or move the process into the explosive zone.
5. Systems that have a high pressure or low vacuum - Leaking airlocks can bleed pressure or allow outside air into a high vacuum, requiring the pressure control system to work harder.

If you have an issue like this, you might want to look at your airlock.  While rotary valves are the industry standard, and currently the only valve approved for explosion isolation in the NFPA, they do constantly leak air into or out of the system.  The reason is the rotor has a small clearance between it and the valves housing.  This allows a path for air to travel.  So while this path is small you will always get some leakage into or out of the system with a rotary valve.

Other valves that will minimize leakage include

• Double dump / knife valve – This valve uses what is essentially two valves in series. And while one of the valves is open, the other is closed.  This prevents air from leaking in or out since there is no direct opening through the valve.  The major drawback of this valve is that the capacity of the valve is severely restricted.  A rotary valve will have a higher flowrate through the same diameter valve.  The other advantages include that these are better with chunky or fibrous materials.
• Trickle valve – A trickle valve (like the Vacu-Valve®) uses the vacuum of the system to seal a sleeve. This prevents air from leaking into the system.  Gravity will then pull the dust through the sleeve once enough material is built up above the valve.  This valve can be used if: the system has negative pressure; the dust is free-flowing dust and won’t bridge; and the dust is not explosive.  The advantages of a trickle valve include no moving parts, low cost, low maintenance, and no power is needed.

In summary, when designing your dust collection system, don’t just pick a rotary valve, make sure that air leakage will not cause an issue.  And if it does, then look for an alternative that will minimize the leak leakage.

Evaluate your current dust collection system for operational efficiency. Simply click the button to get direct access to our evaluation guide.

While not cleaning your baghouse filter is bad, cleaning your filters too much isn’t a very good idea either.  If you don’t clean your filters enough, dust will build up on them faster and they will plug up faster; however, cleaning them too much can cause issues too.

Airlocks are very important for proper dust collector operation.  The airlock prevents air from entering or exiting the bottom of the dust collector.  The opening at the bottom of the dust collector is meant for discharging the dust from the system.  When air is entering or leaving from this area, it will cause issues. 

If the dust collector is under negative pressure (fan after the dust collector), then air will leak into the system from the opening.  This will re-entrain dust that has already been removed from the process air.  This will also decrease the air being captured at the pickup points (hoods), thereby making the dust collection system less effective.

If the dust collector is under positive pressure (fan before the dust collector), then air will blow out of the opening.  This will cause the dust being captured to fly out of the dust collector and scatter on the floor and re-enter the facility air.  Installing an airlock will prevent the above conditions.

Some applications have limitations on humidity, temperature, oxygen levels, etc.  If an airlock is not installed, there will be no way to control the conditions, as the outside environment will leak into the system.

Evaluate your current dust collection system for operational efficiency. Simply click the button to get direct access to our evaluation guide.

Now that winter is winding down, it’s time to get ready for summer!  That means planning vacation with the family!  Cleaning up the yard!  Send the kids outside so they burn off all that energy they accumulated over the winter! 

It’s also a good time to check your dust collector. Now that you will be able to open the doors to your facility without freezing the workers, dust that has accumulated over winter will be dislodged.  And while you shouldn’t have dust layers on your equipment (NFPA specs and OSHA frowns upon it), we all know that it happens at times. 

So now is the time to check your dust collector!

Check for the following and if you have any of them, get your dust collector a checkup.

• High pressure drop
• Dusts exhaust
• Dust piles by the pickups
• Noise from the fan
• Damaged or inoperative airlock

Download Aerodyne DC Evaluation Guide.

Baghouses and cartridge collectors are usually designed to handle a maximum of 6” Water Column (W.C.) of pressure drop.  This means that when the baghouse pressure drop is 6” W.C., the airflow through the system is enough for proper operation.  When the pressure drop across the bags is greater than 6” W.C., the airflow through the system is less than it should be. The baghouse uses a control system to keep the pressure drop through the system less than 6” W.C.  Most baghouses use compressed air to clean the bags, but shaking and sonic cleaners are also used. 

Dust collections systems are complex entities.  They consist of multiple pieces of equipment, and if one of them is not operating correctly, could cause the failure of the whole system.  All dust collection systems consist of the dust collector (cyclone, baghouse, cartridge collector, wet scrubber), exhaust fan, ductwork and hood/pickup points.  Each of these is extremely important to the operation of the system. 

If the dust collector isn’t properly maintained, the system will gradually lose efficiency over time, until it isn’t performing to the optimum.  Often, this isn’t even noticed by the operators because it gradually changes.  However, a new worker or outside observer will notice it, since they will see dust building up around the pickup points.  This gradual efficiency loss can be caused by dust collector issues, dust buildup in the ductwork, or fan issues.  It could also be caused by modifications of the dust collector system after it was installed.

One way to monitor a dust collector system is with pressure drop across the dust collector.  This is a very good way to see if the dust collector is plugging up.  The one issue with this is that if you aren’t constantly monitoring the system, the dust collector could plug up, and a decrease in airflow through it could provide the same pressure drop.  Regular inspections of the dust collector and ductwork should be scheduled to make sure issues are not developing.

Another great way to check your system is to measure the airflow at various parts of your system.  These measurements will tell you if the system is operating correctly.  The reason you want to take multiple measurements is that when you have more than one pickup point, air will travel the path of least resistance.  This means that if one of your pickup points is plugged up, more airflow might be coming from the other pickup points, and the total airflow at the dust collector might be nearly the design amount.  However, the plugged up pickup point isn’t operating as designed.

Often times, dust collection systems are designed for a specific function, then over time, it is changed by either adding or removing pickup points.  This could seriously affect the performance of a dust collector system.  If the changes are made without running calculations, pickup point airflows could change, which could allow dust accumulation around certain areas.

If you have modified your dust collection system in the past, it is a good idea to run some calculations on your system, to make sure it is operating correctly.  If you are planning on modifying your system, design the change so that your system will operate correctly.  If you don’t know if your system has been modified and/or you have dust buildup, check the system design.  If you don’t have the time or expertise for this, consultants can be hired to help you out.

Click here to get a free guide for helping you to evaluate if your current dust collection system is properly and efficiently operating.

Baghouses and cartridge collectors are usually designed to handle a maximum of 6” W.C. of pressure drop.  When the baghouse pressure drop is 6” W.C., the airflow through the system is enough for proper operation.  When the pressure drop across the bags is greater than 6” W.C., the airflow through the system is less than it should be. The baghouse uses a control system to keep the pressure drop through the system to less than 6” W.C.  Most baghouses use compressed air to clean the bags, but shaking and sonic cleaners are also used. 

The two main controllers used are timers and clean on demand.  A timer is a simple controller which will turn on the cleaning cycle at a set time, such as every 5 minutes.  The timer can be changed, and a manual clean is usually available.  While the initial cost of this timer is less, it can end up wasting a lot of money if the timer is cleaning more often than required.  If the timer isn’t cleaning enough, then the dust collector is not operating at its optimal flow.  The other controller option is clean on demand.  This controller uses a differential pressure transmitter to monitor the pressure drop across the bag.  When the pressure drop gets to a certain point, it will begin cleaning the bags until the pressure drop is lowered to an acceptable point.  This can save you a lot of money by minimizing the compressed air required.  However, if your bags are plugged, the cleaning can be continuous as the pressure drop will never fall below the cutoff point.

Filters will have high-pressure drops due to a variety of separate reasons or even a combination of reasons working together.  These include heavy dust loading, wet or humid conditions, worn diffusers, humid compressed air, improper cleaning, and old filters.

1. Heavy dust loading will plug filters faster than lower dust loadings. The faster dust covers the filters, the more the cleaning is required.  However, every cleaning doesn’t get 100% removal so over time the dust layer will get thicker and thicker; thereby, increasing the pressure drop.
2. Wet or humid dust are conditions that can cause premature plugging. When the dust gets wet, it can form a mud.  This could prevent air from passing through, thereby increasing the pressure drop.  If the dust is hygroscopic and/or if the filter is pleated, the filter can plug up even faster.
3. Dirty air entering a baghouse usually goes through a diverter, which directs the air evenly to each bag. Many times the diverter is some metal shape.  Over time, abrasive dust will wear away the diffuser, changing the airflow.  In this case,  some filters will get heavier dust loadings than others.  The filters getting the heavier dust loading will then plug faster, increasing the pressure drop through the system.
4. Humid compressed air can cause major issues with certain dusts. If the dust is hygroscopic, then adding moisture to the system can cause problems.  Some dust becomes a mud while others form a concrete-like substance.  Since the humidity is coming from the cleaning air, the humidity is meeting the dust in the filter holes, thereby plugging them up faster, and making it even harder for them to be cleaned.
5. If the cleaning system isn’t operating properly, the bags will not clean effectively. This could be anything from stuck/broken air valves, misaligned venturi, bags stuck on cages or too low compressed air.  Since the bags are cleaned by an expansion of the bag and losing the dust layer, if air isn’t delivered correctly, the bag may not fully inflate and not fully clean.  So any obstruction or barrier to full inflation would cause premature plugging.
6. As mentioned above, over time all filters will plug up.

The best way to keep your dust collector working properly is to have a professional maintenance crew inspect and maintain your dust collectors.  Not only does this open your maintenance staff for other work, it allows them to use their experience to keep your baghouse operating at peak performance.

Click here to get a free guide for helping you to evaluate if your current dust collection system is properly and efficiently operating.

Baghouses and cartridge collectors often use compressed air / plant air to clean the filters.  By pushing compressed air through the filter, in theory, dust should be removed from the filters.  However,  air compressors are high maintenance pieces of equipment that have high operating costs.  Also, the filters are never completely dust free after an air blast, meaning that, over time they become blinded. This high time-and-monetary cost can be lowered by breaking away from using compressed air and instead using a cyclone pre-filter in your dust collection system.

 By putting a cyclone pre-filter ahead of your filters you can:

• Decrease the loading on filters, reducing their cleaning from twice a minute to possibly once every 2-3 minutes.
• Eliminate the wear and tear on your filters and therefore the risk of your filter developing a hole and compromising the whole filter.

If you are looking to save money on your compressed air usage, a pulse-on-demand controller with a cyclone pre-filter is a good option to explore.

Contact Aerodyne at 440-543-7400 or dc@dustcollectorhq.com to help you problem-solve your dust collection problems.