Filter Bag: The Ultimate FAQ Guide

If you have any question about filter bag, you will find the answer right here.

Among the aspects you will learn include benefits, features, material type, uses and working principle, just to mention a few.

By the end of this guide, you will be an expert in filter bags – let’s dive right in.

What is Filter Bag?

This is a device that controls air pollution and collects dust and other contaminants that industries release into the atmosphere.

It comprises a woven or non-woven filter cloth.

 filter bag

filter bag

What are the Benefits of Filter Bag?

The benefits are:

  • The material is resistant and not sensitive to dust.
  • Also, they can function at high temperatures when you use temperature-resistant materials.
  • The cost of operating is lower than an electrostatic precipitator while it maintains a high deducting efficacy.
  • Besides, the filter bag is simple in design and easy to maintain and operate.
  • It can handle a large volume of emissions.
  • Also, it has high dedusting efficiency of over 99%.

What are the Features of Filter Bag?

These include:

  • A high dust capturing capability.
  • It is lightweight and easy to use.
  • Also, it has a high dust holding capacity.
  • ISO9001 certification.
  • High-temperature resistance.
  • It is affordable to purchase and install.
  • Minimal shrinkage rate.

What are the Uses of a Filter Bag?

Different industries use a filter bag to clean the dirty air it produces.

These uses are:

  • Metallurgy
  • Chemical industries
  • Power generation industries
  • Asphalt mixing industries
  • Foundry
  • Mining industries
  • Carbon black
  • Cement processing
  • Industrial boiler
  • Wastewater power generation plant
  • Tobacco industries
  • Coal-fired boilers
  • Kilns furnaces
  • Petrochemicals
  • Pharmaceuticals
  • Electronic industries
  • Automotive industries
  • Food and beverage industries

What is Differential Pressure in a Filter Bag?

It is the pressure drop difference when you measure across the filter bag from the dirty to the clean side.

This is the measure that provides an accurate reading of the performance of a filter bag.

Personnel can operate the gauges to determine pressure drops on the filter bag.

Besides, it will show you when to make adjustments to it when the pressure readings are too low or too high.

Also, it indicates when it is time to clean the filter bags or conduct intensive maintenance.

What are the Mechanisms of Capturing Particles in a Filter Bag?

These are:


This happens when a particle hits the fiber due to momentum after crossing the fluid streamline.

There is a great chance of impaction occurring when there are large particles and a smaller fiber.

Inertial Collection

Particles hit the fibers perpendicular to the direction of gas flow and not changing direction with the fluid streams.


This is the process of collecting particles that are below the size of 0.5 microns.

Brownian Movement

This process will diffuse sub micrometer particles.

The process increases the possibility of contact between the surface of the filter bag and the particles.

Electrostatic Forces

This mechanism will affect the particles that are below 0.5 microns.

The availability of electrostatic charges on particles and the filter bag will enhance the dust capture capacity.

What are Some Signals of a Bad Filter Bag?

These include:

  • The pick-up points do not collect dust.
  • There is visible dust within the stack emissions.
  • Also, when the differential pressure seems to be too high or too low.
  • The power consumption is higher or lower than normal.
  • There is an increase in usage of compressed air as the pulse-jet cleaning unit is working overtime.
  • After the cleaning cycle, the quantity of dust that falls in the hopper stops or is minimal.

What Material is the Filter Bag Made of?

There are several materials that one can use to make a filter bag.

They include:

  • Nylon
  • Polypropylene
  • Woven wool
  • Porous PTFE film
  • Fluoropolymers
  • Felts
  • Aromatic polyamides
  • Polyester
  • Viscose

How Does a Filter Bag Treat Water?

This device can eliminate contaminants of varying sizes from liquids.

Dirty water will enter the bag filter from the inlet port of the filter housing.

The fluid then flows into the filter bag and the impact of the fluid makes the bag extend.

This extension of the bag makes the filtration process happen evenly.

Thereafter, the fluid will exit via the outlet valves as the solid contaminants collect within the filter bag ready for disposal.

What are the Operational Parameters of a Filter Bag?

Dirty gas will enter the filter bag via the hoppers.

Thereafter, it heads to the filter bag compartment.

Depending on the cleaning technique, the gas passes through the bags on the outside or inside.

A layer of dust will collect on the surface of the filter bag until no more air can move through it.

This is the time to clean the filter bag.

How Can you replace a Filter Bag?

First, make sure the filter bag is not operational.

To remove the bag, shake the basket rapidly.

Thereafter, use a spine movement to separate the filter bag away from the support basket.

Gently pull the filter bag out of the filter bag housing.

It is possible to wash and reuse the filter bag.

Then, replace the filter bag gently within the filter housing.

What are the Benefits of Using Stainless Steel in a Filter Bag Housing?

Stainless steel is one of the strongest materials that you can use to make a bag filter housing.

The benefits are:

  • It will not bend at high temperatures.
  • Stainless Steel is easy to clean.
  • It also provides an aesthetic appeal.
  • Also, it resists degradation from a large pool of agents.
  • It can handle high pressure and low flow rates.

How Can You Test for Quality in a Filter Bag Housing?

The reason for testing is to ensure it can withstand high pressures and is leak-proof.

Some of the testing methods you can conduct are:

Flow Test

This test will calculate the appropriate pressure drop of the filter bag housing.

One can apply water or helium gas depending on the filter type.

Measure the difference between inlet and outlet ports to assess the differential pressure.

Proof and Burst Test

The measurement checks the working pressure of the filter bag housing.

Using oil and pressure 1.5 times the maximum pressure for 30 minutes to verify this test.

Helium Leak Test

This test will ensure that the device is airtight at the connections and seals.

Add helium gas to the filter bag housing for a minute, until it fills with water.

Inspect the seals as you turn up the gas pressure in steps.

What Quality Standards Should a Filter Bag Housing Conform to?

These standards ensure quality filtration and safety.

They are:

  • CE mark of quality
  • ISO 9001:2015
  • ASME code
  • Pressure equipment directive 2014/68/EU
  • 3-A sanitary standard
  • Environmental Protection Agency [EPA]
  • Food and Drug Administration [FDA]
  • Current Good Manufacturing Practices (cGMP)

What Factors Influence the Design of a Filter Bag Housing?

These factors include:

  • Total suspended solids [TSS]
  • Service time
  • The flow rateLibrary
  • Overall cost
  • Operating temperature
  • Method of operation I.e. Batch or continuous.
  • Filtration rating
  • Operating pressure

How Does a Cartridge Filter and Filter Bag Compare?

It is cheap to acquire a filter bag that it is to purchase a cartridge filter.

One can use and reuse a filter bag which is not possible with a cartridge filter.

Filter bags are more durable than cartridge filters.

Both of these are sediment filters.

cartridge filter

cartridge filter

How Does a Coalescing Filter and a Filter Bag Compare?

A coalescing filter will recover clean fluids while a filter bag will clean fluids and air.

coalescing filter

coalescing filter                           

What Features Should You Consider when Buying a Filter Bag?

These include:

Flow Rate

For instance, a multi-bag filter has higher flow rates and less downtime during changeovers.

Micron Rating

Filter bags with big micron ratings enable you to eliminate dirt of any nature.

This will ensure you have a high-efficiency rate while operating this device.

It is advisable to select filter bags with a micron rating of between 0.5 micrometers and 200 micrometers.

Size of Filter Bags

Ensure you select the right size that will fit within the filter bag housing.

This means one should consider both the length and the width.


Make sure you purchase a filter bag from a reputable manufacturer.

This means you will get high-quality and reliable products.

Temperature and Pressure Ratings

The operational temperatures and pressure are vital factors worth considering.


The amount you have will influence the filer bag you can afford.

Quality Standards

Ensure you select a filter bag that conforms to international standards.


Make sure the filter bag is easy to install and replace.

Maintenance Cost

Ensure the filter bag is easy and affordable to repair and replace.

Operating Cost

After installation, the filter bag should function with no extra accessories.

Simplex Versus Duplex Filter Bag Housing

The filter housing you are using will determine the filter bag you will purchase.

What are the Components of a Filter Bag Housing?

The housing contains several parts such as:

Pressure Release Valves

 pressure release valves

pressure release valve

This part will help with regulating the pressure levels in the filter housing.

They make sure the filter housing will not explode or break during the filtration process.

It maintains this by ensuring the pressure will not go beyond the maximum level.


It operates by restricting fluids within the unit from leaking.

Also, it prevents dust from entering the filter bag housing.

Besides, they make sure you achieve the best filtration possible as it securely holds the filter elements in the filter housing.

Always use high-quality caps in the filter housing a slow quality caps may lead to leakages.

Besides, leakages in the filter housing will damage these components.



Check Valve

This part will block air from entering the filter housing after the vent releases it into the environment.

 check valve

check valve

Outlet and Inlet Valves

The inlet port will allow fluids to enter while the outlet ports will help the fluids to exit the filter bag housing.

outlet and inlet valves

inlet and outlet valves


These parts help in eliminating leakages from occurring from the filter bag housing.

o ring

o ring


This part is at the bottom of the system.

It holds all the fluid that did not undergo filtration during the filtration process.


This part will firmly hold the filter bag housing in place.

It can come as flexible and inflexible units.

Small filter bag housings use flexible stands.

Flexible stands enable the operators to alter the position of the filter housing during the filtration process.

Large continuous applications with huge processes make use of inflexible stands.

Inflexible stands are stationary meaning the filter bag housing is also stationary.

Differential Pressure Gauges

This part will monitor the pressure drop in the entire filter housing and will sound an alarm when it is time to replace the elements.

Sample Ports

One will find the incoming and outgoing process fluid ports in these parts.

It helps in drawing inlet and outlet samples to conduct quality tests.

sample ports

sample ports

The Shell

This is the external part of the filter housing and can come from several types of materials.

Most filter BAG housings use high-quality material that can withstand effects such as:

  1. External environmental pressure
  2. Ensure maintenance of chemical compatibility


They direct air within the filter bag housing to exit after it fills with the process fluid.

Also, it is automatic hence will shut once the air escapes into the environment.


This part joins two filter bag housings.

Also, it doubles the capacity of the filter bag housing.

It achieves this by extending the length of the filter thus improving the efficiency of the filtration process.

Besides, they lower the operational costs as they are reusable.




This part seals the bowl after the installation of the filter elements and it holds the pressure release valves, checks valves, and the vent.


This part is at the bottom part of the filter bag housing.

They assist in eliminating products of the sump and also allows you to collect fluid samples in the filter housing.

Also, it will help you to access the elements within the system.

Mounting Holes

This part will help you to fix the filter bag housing in a pipe system.

Also, one can use it to remove the process fluids in the filter housing when you are replacing filter elements.

What are the Types of Filter Bag Housing Available in the Market?

These are:

Single Filter Bag Housing

This system assists in filtering out contaminants from fluids.

Also, they contain one filter bag which you can clean or replace as the need arises.

It contains a basket with perforations on it.

Besides, they are available in varying sizes, pipe, and flange connections.

 single filter bag housing

single filter bag housing

Multi-filter Bag Housing

They are suitable for bulk filtration and are affordable.

The housing contains several filter bags.

Also, the filter bags here are replaceable and are in varying micron ratings.

It can filter solvents, paints, beverages, coolants, etc.

 single filter bag housing multi bag filter housing

multi-bag filter housing

Ensure it meets ASME standard and the following criteria:

  1. Pressure gauge connections.
  2. 150 psig standard pressure design.
  3. Suitable construction material.
  4. Drains with NPT couplings.
  5. An easy to replace filter bag design.
  6. Seal provisions with o-rings.

How Does a Filter Bag Operate?

A stream of fluids with contaminants enters the lower part of the filter hopper.

Dirt and dust particles stick on the surface of the bag as the fluid passes via the filter bag.

Concurrently, clean air or fluids pass out to the outlet as particles collect on the outer portion of the filter bag.

Differential pressure builds up due to the accumulation of dust on the outer part of the bag.

Compressed air will eliminate dust particles on the filter bag after some intervals.

This will result in an opposite flow of air in the filter bag which will remove the particles on the surface of the bag.

What are Some Surface Finishes you Can Find on a Filter Bag Housing?

These finishes will provide an appealing look and include:


Here you will place metal inside a barrel that has abrasives.

The barrel will vibrate making the metals rub against the abrasive products.

It causes the metals to have a shiny appeal to them.

Thermal Deburring

Here, you will remove burrs that come about during the production process.

These burrs arise due to milling, drilling, etc.


This is the opposite of electroplating.

It will rekindle the roughness of the valleys and surface through an electrochemical process.

Electropolishing, through getting rid of thin layers, eliminates:

  1. Pits
  2. Small cracks
  3. Ingrained contaminants
  4. Burrs
  5. Oxide scales
  6. Additional imperfections

This process is suitable for all kinds of steel material.

Also, it offers 30 times more resistance to corrosion than passivation.

After polishing, the surface will have a durable and appealing bright nature.


This method will employ electric current to embed another metal material on the surface of the substrate metal.

The advantages of electroplating are:

  1. It will increase the resistance of the material to corrosion
  2. Also, it improves resistance to wear and tear
  3. Besides, it will increase the aesthetic appeal of the material

Abrasive Blasting or Sandblasting

This method will force an abrasive material on the surface of metals as fluid on high pressure propels the blasting material.

This high-pressure force will:

  1. Smooth rough surfaces
  2. Roughen smooth surfaces
  3. Shape the surface of metals
  4. Eliminate the contaminants on the surface


This method will employ nitric or citric acid to assist in eliminating free iron and extra ferrous impurities.

It will leave behind a resistant and protective layer of oxide that is extremely resistant to corrosion.

Nevertheless, this method is not suitable for stainless steel grades that contain low nickel and chromium levels.

Also, this technique is not suitable for furnishing surfaces that pass welding and brazing.


This technique will use a combination of both nitric and hydrofluoric acid.

It will eliminate the low chromium layer of material and high-temperature scales away from the surface of the filter housing.

These chemicals will also assist in eliminating ferrous materials and ferric acid oxide.

When you remove layers of low chromium, you will increase the resistance of the filter housing to corrosion.

Mechanical and Chemical Planarization

Here you will use chemical and mechanical forces that will smooth the surface of metals.

It is a combination of chemical etching and abrasive polishing.


In this method, you will rub smooth tools on the surface of metals.

The operator applies ample pressure to improve the finishing and the size of the surface.

Industrial Etching

This is a method where you use a strong acid to cut metal surfaces.


This method will eliminate marks and levels and also clean the surface of the metal.

What Can a Filter Bag Housing Come in?

They can come in a horizontal or vertical design.

How do You Test if Filter Bag Housing is Leaking?

The steps are:

  1. Connect the filter bag housing to a tank that has gaseous helium.
  2. Insert the filter bag housing underwater and repeatedly increase the pressure of the helium gas supply.
  3. Repeat this test at 25%, 50%, 75%, and 100% of the maximum working pressure that is allowable.

Continuously monitor the production of the bubbles.

  1. When the bubble production happens for over a minute, it means the filter bag housing is leaking.

How Does a Low-Pressure and High-Pressure Filter Bag Compare?

High-pressure filter bags can handle high pressure while low-pressure filter bags are suitable for low-pressure usages.

low pressure filter

low pressure filter

high pressure filter

high-pressure filter

What Performance Specifications Should You Consider When Selecting a Filter Bag?

These include:

  • Airflow
  • Minimum particle size
  • Pressure drop
  • Gas temperature
  • Opacity

How Should You Maintain a Filter Bag?

Always monitor the differential pressure to ensure its working efficiently.

Regularly clean the filter bag when the dirt accumulates.

What are the Price Determinants of a Filter Bag?

These are:

  • Pressure rating
  • Flow rating
  • Size
  • Design
  • Application

With the information in this guide, you will definitely choose the right filter bag for your unique applications.

However, if you have any other questions or inquiries on filter bags, feel free to contact the Filson Filters team.

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