Having problems with your dust collector? A faulty collector can lead to a shut-down with costly downtime and airborne dust can threaten employee health and safety. Collectors running inefficiently can increase utility costs when valves leak pricey compressed air and fans begin to work overtime to keep up with plugged bags.
Below are four of the most common problems that can occur in a dry dust collection system – and how to fix them.
A filter that isn’t cleaning properly can lead to a high pressure drop, which may reduce the airflow at the dust pick-up points and lead to greater energy consumption. Troubleshoot with these steps:
- Check the hoppers
If you don’t have a rotary valve in the hopper of your collector, make sure that the hoppers have been emptied on a regular basis. Additionally, if you do have a rotary valve, check the hopper to ensure the valve is discharging properly and material is not plugging the collector. Full hoppers may promote re-entrance of dust into the air stream, thus drastically increasing the dust load and potentially overload the dust collector.
Remember, Sly offers hopper flow enhancement designs to prevent this sort of blockage. Call our Aftermarket Parts Department for more information on helpful features and accessories like poke holes, vibrators, fluidizers, level sensors, heaters, and even sonic horns.
- Search for presence of moisture
Excess moisture in the compressed air stream will cause plugging of the bags and may result in improper cleaning and shortened bag life. This moisture should be combated with compressed air dryers.
Additionally, search for any oil leaks, as airborne oil from air compressors can also cause the bags to plug and
interrupt the dust collection system.
- Check the operation of the timer
When checking the timer, observe the LED lights on the circuit board for timer operation. Check the LED’s visually and listen for pulses. Consult the timer manual for details on setting the timer’s pulse duration and frequency of cleaning. For further information, call Sly at 800-334-2957 or consult the video below:
- Inspect solenoid valves
Defective solenoid valves can result in failure of the pulse valves to operate properly or at all. To replace these defective valves, contact our Aftermarket Department and we will find the appropriate replacement.
- Consider condensation
Any condensation of water from high humidity ventilation air entering a cool duct or dust collector can cause the bags to plug. Plugged bags will likely need to be replaced as soon as possible to prevent further problems. Exterior insulation for the dust collector and ducts should be considered.
Problem: The dust collector is operating at a low volume.
Collectors operating at a low volume will pick up an insufficient amount of dust, costing the plant valuable time and money. A low air volume may be due to several factors. Troubleshoot this with the following procedures.
- Clean plugged filter bags
Improper cleaning of filter bags leads to high pressure drop that inevitably leads to a reduced air volume. The filters should be cleaned in an off-line mode, with the fan turned off, for at least 15 minutes. After this time, start the unit up again. If the pressure drop is still high the filters will need to be replaced.
- Evaluate exhaust fan performance
A number of issues could potentially affect the performance of an exhaust fan. Belts may be slipping, rotation of the fan may be incorrect, the inlet or impeller may be in poor condition, or there may be an improper pressure drop due to a poor inlet design for the ductwork. Any specific problems that are found should be corrected and the fan re-tested for flow and pressure drop.
- Inspect inlet ducts
If the inlet ducts are plugged, too small, run too long, or cause an excessive pressure drop due to improper connections or fittings, the system air flow will be affected. Ductwork should be periodically inspected and any specific problems corrected as soon as possible.
NOTE: If a fan damper is supplied, the damper should be closed halfway before startup with a new bag. Once the pressure drop across the bags has reached approximately 2” w.c., the damper may be opened until the unit is at design volume. This is best determined by taking a pitot tube traverse of the inlet or outlet duct of the collector. Any air velocity measuring devices may be used.
Problem: The dust collector is operating at high volume and picking up excessive product.
Collectors operating at excessive volume will pick up too much product, potentially over-working the dust collector and removing valued product from the process. Removing more than just the undesired airborne dust can cost the plant valuable time and money. Troubleshoot as follows:
- Adjust fan speed
If the fan is running at a speed that is higher than design then it will pull too much air through the system causing the pick-up points to draw in excess product. Check the fan speed and change sheaves/pulleys if needed to bring the speed to design conditions.
- Make sure inlet ducts are secure and properly sized
Inlet ducts that are larger than required and not appropriately customized can lead to lower system static loss, which can lead to higher air flow. Check the ductwork static pressure at several locations and across the fan to verify the system pressure drop is per the design conditions. Modify the fan or the ductwork to ensure proper pickup volumes and ductwork velocities to prevent powder from settling in the ducting.
However, before making any adjustments in the ductwork, check for leaks though flanges, access ports or holes and correct those conditions before taking any measurements.
Leaking ductwork will usually mean less available air at the pickup locations and lack of adequate venting of dust in that location. Any non-essential openings should be plugged and any ducting leaks patched to ensure only the appropriate pickup locations are connected to the system.
Once this is done, the current operating volumes and static pressures should be measured throughout the system and include the total readings at the exhaust fan.
Then compare these measurements to the initial start-up bench marks and design of the ductwork. Once these values are known, exhaust air at each pick-up point can be controlled with a blast gate. The blast gates serve to fine tune the amount of air volume (CFM) at the specific ventilation point. If you are concerned about picking up too much product, then the blast gate can be adjusted to a more closed-off position, which creates additional static resistance and decreases CFM.
Keep in mind, a reduction in air volume also means the duct velocity will decrease. Care should be taken to make sure the velocity does not drop below the recommended velocity required to transport the dust to the dust collector. Low velocities will cause the dust to drop out in the ductwork which can lead to serious ventilation problems and safety issues when the ductwork fills with material. The hood design should also be observed for velocities that are too high, allowing pick up of more dust.
Thinking about this process as “dust control” and not “dust collection” may help put it into perspective. For example, a pick-up point should have a hood or transition which keeps the pick-up velocity low as compared to the high-velocity transport in the ductwork. These values will vary dependent on the application and type of dust involved.
- Check filter bags
Any missing or damaged filter bags will create a lower system static loss that can lead to higher conveying air volumes (based on fan curves). The greater problem here is not “excessive product pick-up” at the dust source but heavier dust emissions. Refer to the next section for troubleshooting recommendations.
Problem: The dust collector is experiencing excessive dust leakage.
This problem is similar to excessive product pickup, but is unrelated to collector volume conditions. Instead, troubleshoot dust leakage as follows:
- Double check filter bags
If excessive dust leakage is occurring, first check to make sure the filter bags are installed properly. Any improperly installed filters should be reinstalled. Look for telltale signs of dust on the tubesheet around the faulty filters.
- Inspect clean-air-plenum for leaks
Visually inspect the clean-air-plenum to find the source of the dust leak. If you cannot determine the source of the leak, fluorescent powders are available which glow under black light.
In a dye test, a quantity of the fluorescent powder is introduced into the inlet of the collector with the fan running and the cleaning system off. Use approximately 1/2 pound of powder per 1,000 square feet of media. Next, the fan should be turned off and the clean-air-plenum inspected with the black light. The leak point will glow a bright fluorescent color that is more apparent in dim or dark surroundings. A leak test kit is available from Sly Inc.
Keeping your dust collection equipment in proper operating condition is essential to maintaining compliance with EPA and OSHA regulations as well as maximizing product recovery. Troubleshooting is a critical part of the overall system operation. Paying close attention to small changes in the operation becomes key to keeping your system running smoothly in the way it was intended.