Now, in this section, I am going to take you through the critical elements of a bag filter.  And, I will start with:

What is Bag Filter?

A bag Filter or Filter vessel is an air and fluid pollution/contamination control device.

It helps to remove particulates from an air or a fluid stream released from any commercial process.

Filter bags are fabric designed with the intention to remove particulate material from the fluid.

The Filter bags are always inside the housing which is sealed.

Bag Filter

There are two types of bag filter housing namely;

1. A single bag filter housing
2. Multi-bag filter housing

I will come to that later in this guide, keep reading.

Also, the bag filters come in different designs to cater to a range of applications. For example, you may have water treatment bag filters, stainless steel bag filter housing, liquid bag filter housing, etc.

Bag Filter Working Principle

Fluid stream polluted with particulates under pressure or suction enters the lower portion of the bag filter hopper.

As the fluid travels through the bag filter, the dirt or dust particles remain on the bag’s surface. At the same time, clean air or fluids will pass out through the bag to its outlet.

It means that the particulates collect on the outside part of the filter bags.

This accumulation of dust on the outside of the bag results in differential pressure across the filter bags.

After some intervals, it uses compressed air to remove accumulated dust on the bag filter.

That is, put out the bag filter from its vessel and then using compressed air, flush it or replace a new one.

It results in a reverse flow of air via the filter bags, hence dislodging the dust particles on the outside surface of the filter bags.

The processes release all dust particles on the bag filter.

There are two types of bag filter housings.

The first design has only one filter bag. On the other hand, the second option has several filter bags.

i. Single Bag Filter Housing

Single bag filter housing helps in filtering away contaminants from a stream of fluid.

They accommodate one filter bag at a time, which can either be cleaned or replaced whenever there is a need.

Look at this:

Single Bag Filter

The single bag filter has a perforated basket that supports it.

When unfiltered fluid enters the housing, the solid particles are within the basket for removal.

It has working pressures ranging from 100 PSI to 300 PSI with a maximum working temperature of 300 Degrees Farads.

They feature different materials such as:

• Aluminum
• Carbon steel
• Stainless steel 316 or 304

Depending on the model of the single bag filter one needs, they come in different standard sizes with different pipe connection styles, sizes, and different flange connections.

High-pressure single filter housings can also be made depending on the customer’s requirement.

It has a v-clamp cover closure which makes changing bags fast and easy without the use of any tool.

• ASME CODE Bag Filter

This type of filter housing must conform to the international code of standards.

Upon request from the customer, the manufacturer designs, tests, and stamps the bag filter as per the ASME BPV code section VIII.

This will ensure that it works under the specified conditions.

The standard features may include;

• Constructed from stainless steel material
• Maximum Design Pressure of 300 PSI at a Temperature of 300 Degree Farads.
• Will have Gauge Ports¼” FNPT
• Drain Port, such as 1” FNPT
• Vent Port, such as ¼” FNPT
• Flanged/thread Connections
• Buna N O-Rings
• Perforated Basket of Stainless Steel (304 types)
• Mirror polish
• Typical Flow Rate of between 50 – 125gpm
• Adjustable Legs

This product can also have several optional features which may include;

• Carbon steel material
• Maximum design pressure of 1440psi or higher
• Different connection styles and sizes
• Baskets lined with Mesh
• Davit arm for higher pressure units.

ii. Multi Bag Filter Housing

These are very economical for bulk filtration.

The housing can accommodate many bags within one vessel.

Filter bags in multi-bag filter housing are replaceable and come in different micron ratings.

Multi Bag Filter Housing

You can use multi-bag filter housing to filter solvents, beverages, water, coolants, glues, inks, recycled oil, paints, etc.

Before, you buy any multi-bag filter housing, ensure it conforms to the ASME standards. Besides, it should meet the following criteria:

• Standard design pressure of 150psig
• An O-ring closure seal provision
• Design whose bag filter is easy to replace
• Suitable material
• NPT couplings for drain
• Pressure gauge connections
• Vent

Please note:

All housing whose dimensions are less than 12 inches (305mm) should have handles.

However, those housings with more than 12 inches have head lifts provisions. Also, they have a provision for a 150 lb ANSI RF flanged inlet/outlet.

Remember, depending on the nature of the application at hand; you specify optional accessories.

The multi-bag filter housing possesses several basket strainers.

Of course, this is essential for high filtering capability since it will give a wide range of flow capability.

They are designed to contain very many baskets.

The system comes with steel baskets with mesh liners. Thus you can use them as strainers.

Like filters, the stainless steel basket has a perforated design to hold disposable or cleanable filter bags.

I know there are many types of bag filter housing material out there. Normally, the type of material will depend on the nature of the application.

In this section, I will focus on two types of filter housing material. They include:

a) Stainless Steel Bag Filter Housing

The main material here is stainless steel.

Stainless Steel Bag Filter Housing

It is due to the varying conditions under which filtration may occur.

The most common grades of stainless steel for this application include 304 stainless steel (SS 304) and 316 stainless steel (SS316).

So, what’s the difference between these two types of stainless steel?

SS304 is an alloy of 18% chromium and 8% nickel. On the other hand, SS316 is an alloy of 10% nickel, 2% molybdenum, and 16% chromium.

Here, molybdenum makes stainless steel, highly corrosion resistant.

It makes stainless steel perform better in any condition of operation.

Type 304 stainless steel, for example, is capable of resisting corrosion and oxidation.

They can, therefore, work perfectly well in conditions where the temperature is elevated and a high degree of oxygen concentration.

When the housing is fabricated using SS 304, it exhibits a good surface finish. It is a property that prevents product contamination during the filtration process.

You can use it in a variety of applications such as pressure vessels, tanks, tubing, or piping.

SS 316 on the other side is known to have high heat resistance due to its chemical composition.

When exposed to different types of chemical solutions, it portrays high corrosion resistance.

The property is due to components such as nickel-chromium.

The addition of Molybdenum to SS 316 makes it highly resistant to attack by chemicals than SS 304.

It, therefore, follows that SS 316 is long-lasting and easy to handle during fabrication. This gives its final product a good surface finish which makes it easy to clean.

At elevated temperatures, it is more resistant to solutions of chlorides, sulfuric acid, iodides, bromides, and fatty acids.

Its composition has molybdenum, which makes it suitable for most filtration purposes in the pharmaceutical industry to prevent excessive metallic contamination.

There are also other forms of stainless steel that can be used depending on the conditions under which filtration takes place.

A good example of such material is the duplex stainless steel: UNS S32760.

UNS S32760 is designed to have high impact strength at zero temperature and gives excellent corrosion resistance.

It is also affordable and made up of 25% chromium, 7% nickel, 3.6% molybdenum as well as copper and tungsten.

Key areas of applications include desalination plants, seawater systems, etc.

b) Carbon Bag Filter Housing

These bag filter vessels adopt high-quality carbon. The main applications include petrol chemicals, wastewater treatment, rubber industries, etc.

Carbon Bag Filter Housing

Compared to stainless steel material, it is lower in cost.

When it comes to filtration systems, you can choose either bag filters or cartridge filters.

Cartridge Filter vs. Bag Filters

Whether to go for a bag filter or cartridge filter will depend on the nature of the application at hand.

And, in this section, I am going to walk you through just a few:

1. Type of Applications

Cartridge filters are suitable for both surface and depth-type filtration applications.

On the other hand, bag filters are popular in most industries as dust removers, and they can be used repeatedly to save cost.

2. Working Principle

Let’s get this right:

The two types of filters help to eliminate or reduce the contamination level.

However, there are two distinct concepts you should know:

Bag filters are such that the separation occurs at the surface of the filter membrane. While for the cartridge filters, the separation can occur either on the surface or through the thickness of the filter materials.

3. Cost of Filter

Bag filter housing normally requires low investment – you can use them several times.

Cartridge filters together with water filters are prone to replacement. You can replace them many times within a small time span.

Also, bag filters can last for more than 5 to 10 times the ordinary filters. Therefore, this reduces the cost of using bag filters.

Whenever you’re buying a bag filter, there are some things you should consider. It is only through this that you will get everything right.

Let me take you through this critical element:

• Simplex vs. Duplex Bag Filter Housing

You may choose a system with only a single or two housings.

They will perform the same purpose. However, in situations where you want continuous and uninterrupted flow, duplex bag filter housing is the best.

Even during filter element changeover, you don’t have to stop the entire system. Therefore, you don’t have to worry about possible downtime.

• Quick Access Covers

The cover should be easy to open and close with minimal time taken.

There is no need to use other tools during the opening, but instead, provide a clamp and spring for easy opening and closing.

Multi Bag Filter Housing

Still, ensure the cover has the right safety measures. That is one that prevents the cover from opening by itself.

So, you must scrutinize the design of the cover.

• Low Profile Design Housing

The housing design should be compact since you will use much equipment at ago.

It should have a good working space to facilitate easy removal, cleaning, and maintenance of the bags.

The design should be one that does not require ladders or climbing platforms. These can be safety hazards.

A low profile provides easy access, and balanced spring lids can be opened with one hand.

• Flow Rate

Deciding to buy the best bag filter may be challenging, but can depend on the flow rate required.

A multi-bag filtration system, for example, comes with some advantages which may include higher flow rates with less downtime during bag changeover.

• Micron Rating

Having filter bags of a big micron rating allows the removal of particulates of any nature. This gives high efficiency during operation.

It is, therefore, necessary to choose the bag filters with a micron rating between 0.5μm and 200μm

• Pressure and Temperature Rating

Working temperature and pressure are important parameters you should consider when buying a bag filter housing.

Operating bag filter systems beyond a specific threshold can be catastrophic. It will damage the filter system.

For example, the most multi-bag filter housing can work at a pressure of up to 1.5 Mpa and a temperature of up to 250 degrees Farads.

• Filter Bag Sizes

You must choose the correct size of filter bags that can fit in the housing. You should consider both the width and length.

Apart from all these, you must buy the bag filter housing from a reputable manufacturer. This way, you will get bag filter housing that guarantees “zero leakage” and exemplary performance.

At this juncture, I am sure you can assess and buy the right bag filter housing. Of course, this is after going through the basic definition, classification, standards, material, and factors to consider in bag filter housings.

Now, I would also wish to hear from you.

Which brand of bag filter housing are you using?

Are there problems with your hydraulic filtration system?

Talk to us today – At Filson Filters we offer free consultation on hydraulic filtration systems.