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Baghouse Tips with Dr. Vent Goode

Are your system’s ventilation hoods effective?

Vent hoods are the point where gasses are suctioned into your ventilation system.  They are a very important component in the performance of your baghouse and discharge system, yet designers often pay little attention to their design and location.

To understand hooding design, first we need to understand the purpose of your ventilation system.  Or more precisely, what it’s not supposed to do.  With a few exceptions in process equipment, the ventilation system is NOT intended to suction dust.  Its purpose is just to keep your process equipment or your enclosure under negative pressure.  Some dust will inevitably end up in the baghouse, but it’s not intended to act like a vacuum cleaner.

Hoods have two basic functions:  They should minimize material carryover and they should minimize pressure losses at the pick-up points.  These two objectives can be accomplished with proper hooding design.

In a nutshell, the larger the hood, the lower the amount of dust suctioned.  And the more tapered, the lower resistance to flow.  There is obviously a physical and cost limitation, so rule-of-thumb guidelines are presented in design manuals to make them reasonably sized.  The typical recommendation is to form a square box as wide as the enclosure allows before tapering to the round ductwork.


Hooding position is also important to minimize material carryover.  Even a properly designed hood will end up suctioning excess material if it’s placed at the wrong location.  In general, hoods must be placed away from the source of dusting, as shown below.


Properly designed and properly positioned hoods can make a big difference in your systems’ performance to reduce wear on filter bags and discharge system overload.

Call us to discuss your application with one of our engineers today!

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Cost effective ways to improve your pulse-jet baghouse

If you’re thinking about replacing your pulse-jet baghouse due to failing performance but don’t have the funds to do so, read on. Many times you don’t need to replace a low performing pulse-jet baghouse, as there are some cost effective steps that can be taken to keep the baghouse running efficiently.

Installing filter bags properly

Making sure the filter bags are installed correctly is a cost effective way to increase the life of the bags. An often overlooked technique for installing filter bags is utilizing a pinch in the fabric filter. Sometimes bags can become too loose on the cage resulting in limited collection efficiency and/or premature failure. By pinching the fabric of the bag you will tighten the fit to the cage which will allow you to maximize the performance and life of your bags. To determine the proper pinch you need to subtract the cage circumference from the bag circumference and divide the result by 2. Use the chart below to determine the amount of excess fabric to allow based on the bag type, and what the recommended support cage would be.

bag pinch diagram

Fabric Pinch Recommended Support Cage
Felt 0.25″-0.75″
(6.4-19 mm)
membrane on felt
(1.6-7.9 mm)
PPS 0.25″-0.5″
(6.4-12.7 mm)
P84** 0.125″-0.375″
(3.2-9.5 mm)
Fiberglass 0.125″-0.375″
(3.2-9.5 mm)


Automate the pulse cleaning cycle

Creating an on demand cleaning cycle for your baghouse will optimize the energy efficiency, saving compressed air and operating costs. Using the combination of a Photohelic pressure switch and gauge adds the ability for an automated cleaning cycle. This Photohelic combination allows the differential pressure to be automatically monitored in order for it to determine when to begin the pulsing process. You can adjust the settings of the equipment so that when the differential pressure becomes too high the cleaning cycle begins, and when the differential pressure lowers to a desired point the cleaning shuts off. Not only does the switch and gauge save energy, it saves your staff time from having to constantly monitor the differential pressure levels and manually operate the cleaning cycle.

Use pre-coat powder

Applying pre-coat powder when installing a new filter bag will improve filtration efficiency. When new bags are placed in a baghouse, they do not have the initial dust cake buildup to help filter the airflow. A bag without a dust cake is susceptible to moisture which can result in a higher differential pressure. As mentioned previously a high differential pressure means a pulsing cycle is necessary resulting in energy consumption, and too much pulsing can decrease the bag life. The image below shows the results of a test conducted on bags with and without pre-coat powder.

Utilizing a leak detection kit

The longer a filter bag is used the more likely it is to get a tear in the bag. Manually inspecting the bags for rips or tears is one way to test for leaks, but this can be time consuming requiring a longer shut down period of the baghouse. Often times manually inspecting each bag can lead to overlooked leaks that may be too small to catch on the initial glance. Using a leak detection kit ensures accuracy and is the fastest way to check for any holes in the bags. The kit consists of two main components; the ultra violet leak detection powder and the blue LED test light. First apply the powder into the dirty air side of the dust collector. After application use the LED light to inspect the clean air plenum of the baghouse. The powder will have a bright glow under the test light around the bags where there are leaks. Leak detection powder can also detect torn seams, improper installation, cracked tube sheets, broken welds, and more.

Dust collectors are complex equipment that take time and effort to maintain. If you take the proper steps in taking care of the filter bags and optimizing the cleaning cycle, you can increase the life and efficiency of your pulse-jet baghouse.

Baghouse Tips with Dr. Vent Goode

Questions about round dust collectors


dr vent goode illustration


Recently the following question came in for Dr. Vent Goode: “For round collectors, what are the provisions to control the gas to individual dust collectors?  How will even, constant, flow be directed to each bag house?”

Dr. Vent Goode’s answer

Good flow distribution is important to maximize performance on any multiple module baghouse, with circular modules or not.  I’m glad you bring this up, because this effort begins at the plant layout stage.  There are also three more important considerations to optimize flow distribution, per the following:


We want to make sure that the inlet to the baghouse and the outlet to the fan are on opposite sides of a multiple module baghouse.  An example is that if you have an east and west modules with the inlet coming from the west, then the outlet and the fan should be on the east side.  If the inlet is from the south, then the outlet should be to the north, not the east or west.

An example of a poor layout on a baghouse would be when a two-module unit has an inlet from the south, with the outlet and fan to the east.  The result is that the east module sees a lot more loading because the fan tends to ‘pull’ more on that side.

Sometimes, a perfect layout simply cannot be implemented.  In those cases, the outlet of a given compartment(s) can be partially restricted with a flat plate to help apply similar fan suction to each module.  CFD studies can be made for complex situations.  Note that restricting the inlets (dusty flow) is not recommended because of abrasion.

Duct Branching and Sizes

The inlet flanges into the two modules are the same, both sized to handle the required flow.  Both come from a main duct that splits into the two smaller diameters, keeping velocities constant.  There are well established guidelines to design this split/reduction.

The same goes for the outlets.  Both similarly sized outlet ducts join to a larger main duct going to the fan.  Proper design of this connection is simple, but important.  I also recommend avoiding extra elbows or detours that would make one module have more flow restriction than the other.

Cleaning Controller

The baghouse should have a single controller that follows a defined cleaning sequence that pulses all rows before starting the sequence again.  Having two controllers, each pulsing as necessary, is definitely not recommended because the compartment with more loading will end up pulsing more, accelerating wear on the loaded compartment and exacerbating the balance problem.

With the recommended setup, the loaded compartment will accumulate more material.  Since it cleans the same frequency as the other compartments, the additional material will send more flow to the ‘cleaner’ compartment, helping the system self-balance.


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What you didn’t know about baghouse start-up


baghouse with silos

One of the core operations of IAC business is providing routine maintenance and inspection programs with the plants we work with. After many years of conducting inspections, repairs and start-ups we’ve noticed trends where the plants we work with are unaware of aspects involving maintenance. One particular issue that consistently arises involves pre-baghouse start-up inspections. Not only do we want to help our customers maintain their equipment, we want to educate them as well to avoid future issues.

IAC recently visited a plant to review and inspect the installation of the baghouses and related equipment in preparation for the upcoming startup. The following is a brief summary of the work performed and some recommendations to get the most out of your equipment.


Scope of Work

The request was to inspect 3 recently installed baghouses and test them for proper operation. The IAC “Blue Crew” checked for proper bag installation by reinstalling three bags in each unit and making sure all of the cages were properly seated on the tube sheet, which can indicate bag installation errors. Pulse pressure, controller settings and pulsing of all pulse valves were checked before checking the airlocks and activating fans to check for proper fan rotation. We also performed initial flow balancing to avoid over venting once the plant starts. Verification and secondary adjustment is recommended after the filter bags build up the recommended differential pressure.


General Recommendations

  1. Install compressed air regulators and adjust pulse pressure to approximately 80 psi. This applies for all IAC auxiliary baghouses. Compressed air is currently connected to the plant air system at 120 psi, which exceeds the recommended maximum for the pulse valves and will cause unnecessary wear on the filter bags.


  1. Program controllers with 160 millisecond pulse duration (on time) and time between pulses of 15 seconds (off time). This was done for the systems inspected.


  1. Program the controller to activate pulsing at the recommended high-levels (high pulse) and stop pulsing at a point slightly below that to maintain a uniform ΔP and avoid surges in discharged material. This was done for the three systems inspected.


  1. Because of extensive horizontal duct runs, we recommended non-restrictive duct inspection doors and periodically inspecting and cleaning buildup as required.


Other Observations

  1. Unnecessary openings on belt transfer enclosures need to be eliminated. De-dusting systems work by suctioning a draft of ambient air through necessary enclosure openings, avoiding dust emissions by sweeping fugitive dust. Large, unnecessary enclosure openings nullify capture velocity, reducing the effectiveness of the system.


  1. Adequate skirting at the enclosures need to be installed. Skirting is part of the enclosures, but was missing, leaving a much larger opening than necessary. As explained above, large openings nullify capture velocity and reduce


  1. Several vent hoods were positioned right next to the belt loading point, which cause some dust recirculation. Hoods work more efficiently when positioned farther away from the belt load point; closer to the end of the enclosure to reduce carryover.
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Abrasion Resistant Elbows

Elbow Overview

Wear problems are common in pneumatic conveying systems with high velocities. Sometimes bulky material that’s being conveyed will slide along the elbow wall at a high velocity upon which the centrifugal forces press this material against the outer metal surface. The resulting friction causes the elbow walls to wear out quickly.  Even thick steel or cast iron elbows can wear out over time.

Ceramic Backed Elbows


Ceramic Backed elbows are designed to eliminate unwanted costs such as maintenance, loss of material, and down time.  Ceramic Backed elbows are customly manufactured so that they can remain in systems much longer, reducing costs, and increasing production.

How they operate

The Ceramic Backed elbow has a jacket across the back of the core elbow (which is approximately ½” of ceramic compound). This compound has a Mohs hardness of 9+, second only to diamond, which has a Mohs hardness of 10. The ceramic jacket and core elbow is then wrapped with an exterior material to maintain hoop strength. Once the core elbow has worn through, the abrasion is then transferred to the ceramic outer jacket. The metal core also acts as a static conductor.

  • Abrasion Resistant
  • Easily replaces existing elbows
  • Does not change line flow
  • Ceramic is applied to the back of the elbow, then wrapped in a reinforced material to maintain hoop strength
  • Available in CS, SS, Alum, and Galvanized Steel
  • Available in Pipe or Tube
  • Available in many degrees & CLR’s
  • 8x-10x the life of raw steel


  • Activated Carbon
  • Chemicals (Calcium Carbonate, Titanium Dioxide, Alumina Powder, etc.)
  • Fine Sand
  • Glass
  • Lime
  • PVC compounds
  • Fine Plastic Regrind
  • Wood by-products
  • Calcinar Dust
  • Fine Metal Shavings


  • Ceramic Backed works well against abrasion, but NOT against impact

Ceramic Flat-Backed Elbows


Ceramic Flat-Backed elbows are designed and manufactured for tremendously abrasive applications.  These elbows utilize pipes or tubes for the inner core substrate, which lessens the wear caused by the outlet transition, which is no longer needed (going from square back to round).

  • Highly Abrasion Resistant
  • Impact Resistant
  • Easily replaces existing elbows
  • Does not change line flow
  • Available in many degrees & CLR’s
  • Available in CS and SS
  • Available in Pipe or Tube

Typical Applications

  • Foundry Sand
  • Fiber Glass Filled Products
  • Fly Ash
  • Coal Fines
  • Aggregates
  • Hard Pebble Lime
  • Dirty Grain (w/ sticks & rocks)
  • Soybean Hulls
  • Large Metal shavings
  • Large Particulate applications

Cast-Backed Elbows


Cast-Backed elbows are designed and manufactured to withstand the impact of large particulate pneumatic conveying.  These elbows consist of a ¾” thick interlocking back tile, which also offers an additional ¼” thick slide protection.

  • Highly Abrasion Resistant
  • Impact Resistant
  • Easily replaces existing elbows
  • Does not change line flow
  • Available in many degrees & most standard CLR’s
  • Available in CS, SS, Aluminum, and Galvanized Steel
  • Available in 2”, 3”, 4”, & 5” pipe sizes
  • Available in 3” & 4” tube sizes


  • Cast-Backed elbows are only available in 2”, 3”, 4”, and 5” pipe sizes, and can be adapted to 2”, 3”,4”, and 5” tube sizes

Specialty Elbows

Replaceable-Back Elbows

  • The Replaceable-Back Elbow is constructed from a pipe or tube elbow. The sides are constructed of 10GA material welded to the bend.  The back of the elbow is constructed of 10GA material, but 10GA AR plates and ¼” is also available.  The back plate can be replaced as needed and extra back plates are available at the time of the purchase.

Hollow-Back Elbows

  • Progressive’s Hollow-Back elbows are designed to capture abrasive product in the fabricated back cavity. The abrasive material then rides against itself.  The Hollow-Back elbows are fabricated using a tube or pipe elbow, thus eliminating the need for transitions.

Mortar-Filled (Cement Back) Elbows

  • This elbow is similar to the Hollow Back Elbow, but the cavity is filled with hard concrete, or refractory for high heat applications. A standard or custom mix concrete can be used.
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How to Install and Maintenance a Sonic Horn

What is a Sonic Horn?

Sonic or “Acoustic” horns are manufactured and designed for the purpose to produce and amplify low frequency sound vibrations at high intensity for removal of unwanted particulate or excessive material build-up or bridging.

Step by Step Safety Measures


Long term exposure to intense sound without hearing protection may cause permanent hearing loss.  For further details and information regarding this issue, visit the website for OSHA Safety Regulations.


Correct Sonic Horn location is critically important for maximum sound intensity and optimum sonic cleaning results.

Internal vs. External Installation

  • If internal installation is required, a chain supporting system is recommended
  • If external installation is required, it is recommended that the Sonic Horn be bolted or clamped to a flange to allow future removal for maintenance and inspection. If mounted to a hot surface, a complete insulation unit is recommended to prevent moisture and condensation from accumulating inside the driver and bell.
  • DO NOT REMOVE the sonic horn’s reducer for the air supply chain
  • DO NOT USE pipe tape to make piping connections


The optimum performance of a sonic or acoustic horn can be achieved by setting the air regulator to supply 70 to 80 psig continuously through a ¾ pipe during sounding.

  • A Start-Up sequence is recommended to test and evaluate the Sonic Horn’s cleaning process before establishing which amount of time is required for optimum cleaning, and the extension of your diaphragms life.
  • It is recommended that the Sonic Horn should only operate as long as required to extend diaphragm plate life and minimize driver wear. The typical diaphragm life is approximately 400-750 hours.


Inspections are recommended every 3 to 6 months.  The most important part of the sonic horn that requires regular inspection or maintenance is the driver, which has 3 parts: the driver “body,” diaphragm, and driver lid.  When inspecting or troubleshooting the driver, the following steps should be taken:

  • Check air pressure as close to the horn as possible (minimum of 70 psig and a maximum of 80 psig are optimal)
  • Remove driver lid and inspect the seat for any sort of debris buildup (this should be a clean surface). If there is any sign of wear, it should be replaced.
  • Remove the diaphragm plate and check for cracks and wear on the outer edge. If wear on the plate is greater than a depth of .002 to .004 then the diaphragm should be replaced.
  • Clean the driver body cavity with oiled cloth, removing all rust and debris. The seating surface that the diaphragm contacts against must be smooth and free of foreign build-up.
  • Re-assemble the driver and test the operating performance with a pressure gauge (0-15 psig) utilizing 1/4“NPT threads. Attach gauge to the ¼” NPT opening where the ¼” pipe plug is on the driver lid.  The gauge should read between ½ and 5 psig if the Sonic Horn is operating properly.

For further assistance, please do not hesitate to call an IAC representative.

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The Basics of Industrial Fans

Why Industrial Fans Matter

An industrial fan’s purpose is to provide a large flow of air or gas to various processes. This is usually directed through a rotation of blades which are connected to a hub/shaft, and driven by a motor.

Industrial Fan Basics

There are numerous uses for the continuous flow of air or gas that industrial fans generate, including: combustion, ventilation, exhaust, and particulate transport to name a few. Fans operate in both clockwise and counterclockwise orientations, and common accessories for fans include: flanges, shaft seals, belts, and bearing guards. Belt/shafts and bearing guards are extremely important as OSHA requires it – they are an absolute must!

The Two Primary Types of Industrial Fans

Centrifugal Fans

Centrifugal fans utilize what’s known as a “centrifugal force” generated by a rotating disk, with blades mounted at the right angles to the disk, to impart movement to the air or gas stream and increase its pressure. In contrast to axial fans, centrifugal fans/blowers use wheels rather than propellers. The centrifugal fan wheel is typically contained within a scroll-shaped fan housing. The air or gas inside the spinning fan is thrown off the outside of the wheel to an outlet at the housings’ largest diameter. There are a variety of centrifugal fans, which may have fan wheels that range from less than a foot to over 16 feet.

Axial Fans

An axial fan design utilizes axial forces to achieve the movement of the air or gas, spinning a central hub with blades extending radially from its outer diameter. Unlike the centrifugal fan, axial fans utilize propellers rather than wheels. The axial fan is often contained within a short section of cylindrical ductwork, to which inlet and outlet ducting can be connected. Axial fan types have fan propellers with diameters that usually range from less than a foot to over 30ft. Simply put, axial fans are used where the principal requirement is for a large volume of flow, and the centrifugal design where both flow and higher pressures are required.
There are numerous subset designs within each of these groups to meet the specific needs of your process (backward-inclined, shrouded radial, paddle wheel, air foil, tube axial, etc…). For more information, please visit our IAC Fan page.

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Importance of Measuring Dust Build-up with Combustible Materials

With the EPA, NFPA, and OSHA cracking down on industrial facilities and plants more than ever in regards to combustible dust and explosion prevention systems – especially those involved with dairy, wood, or mineral processing – keeping up with regulations and maintaining a safe environment has become more imperative than ever.  Combustible dust mitigation and risk analysis are a large component of our business, and this applies to many of our customers.  In regards to combustible dust control, the NFPA has stated any and all dust collection, pneumatic conveying and/or vacuum cleaning systems which handle combustible dust need to be designed in a manner so that air velocity traveling through these systems meets or surpass the minimum-requirements. This will help ensure the piping/duct surfaces remain free of agglomeration under all standard operating modes.  Furthermore, the NFPA has stated that if “the system’s filter-receiver or dust collector has an enclosure (dirty side) volume greater than 8 cubic feet, the enclosure must be protected against an explosion’s effects by a valid protection method, such as an explosion venting, suppression, or containment system.”

If dust buildup is not properly evaluated (maintenance), combustible products serve as a huge risk.  For example, grain loading, sugar, and wheat plants have to be extremely cautious, as the static electricity caused from the fine particles can cause explosions – and in rare cases large explosions resulting in deaths of employees.

Kst & Pmax Testing

Kst and Pmax are the explosive properties and values, which upon tested, will tell you how much pressure an explosion will produce and how fast the explosion will travel.  This is what’s known as the “Explosion Severity Test.”

Pmax = maximum pressure of a dust cloud explosion

Kst = speed of the pressure

Why it’s important

This test is extremely important for manufacturers when used to validate the design of protection systems (explosion venting, explosion suppression, etc).  The “explosion severity test” will also allow you to find out what “class” the sample you test falls within – which are listed below:

ST class 0 – KSt value = 0

ST class 1 – KSt value less than 200 bar m/sec and greater than 0

ST class 2 – KSt value between 200 and 300 bar m/sec

ST class 3 – KSt value greater than 300 bar m/sec

Grain dust 89 bar.m/sec 9.3 bar g ST1
Coal dust 85 bar.m/sec 6.4 bar g ST1
Flour 63 bar.m/sec 9.7 bar g ST1
Sugar 138 bar.m/sec 8.5 bar g ST1
Wood dust 224 bar.m/sec 10.3 bar g ST2
Aluminium dust 515 bar.m/sec 11.2 bar g ST3
Sewage sludge 102 bar.m/sec 8.1 bar g ST1
GRP dust 216 bar.m/sec 7.6 bar g ST1