Filter bags are used in a multitude for industrial applications. Whether you are working on your first filter bag system or rebuilding an existing system, the following pages provide the information needed to understand filter bag systems and how they work.

FilterbagsNetherlands will guide you through the types of filter bag systems, the definition of a micron, the types of filter bag media, and filter bag efficiency.

Filter Bag Systems
What is a micron?
Filter Bag Media

Filter Bag Systems
There are two basic types of filter bag systems: open systems and closed systems.

Open System
An open system is the most economical bag filter system that consists of a filter bag that is simply tied to a pipe or attached to an adapter head through which unfiltered liquid passes.

Strapped filter bag system
Adapter head system
Adaptability is a clear advantage of a tie-up filter bag system. Because no special hardware is required, tie-up filter bags offer versatility and simplicity for many industrial applications. Any medium, any shape, any size, we can produce to your exact specifications.

Strainer Bag System Perhaps the simplest filter bag is the pressureless free flow strainer bag (gravity). These bags can be manufactured from almost any media, but are most often made from polyester and nylon woven media. Available in a variety of standard sizes. These sieve bags are produced with an elastic, a drawstring, or a rough top. They are the most economical choice for coarse gravity flow filtration.

The adapter head system is a low-cost, easy-to-use solution for gravity or low-pressure filtration. Filter bags for the adapter head system can be of any combination of media/micron. They are installed by simply sliding the ring over the adapter head and securing the bag, creating a positive seal. The filter bag can be removed quickly and easily, without clamps or tools. For even easier replacement, our filter bags come with integral handles and custom ring size for a perfect fit. The lack of a seam knob makes filtration bypass-free.

Note: For pressures higher than 10 psi, a stainless steel filter basket is recommended.

Filter bag mounted on adapter head
Filter Bag mounted on Adapter Head System
Adapter Head Filter Bag

Closed System
A closed system is a filtration system under pressure. Liquid is passed through an inlet of a filter vessel into the top of a filter bag supported by a retainer basket. The liquid moves through the supported filter medium where the contaminant is trapped. The cleaned filtrate exits the filter vessel through an outlet connection. The contaminated particles are retained in the filter bag for easy replacement and removal. The filter medium in the filter bag is selected based on the particle size required.


Longer service life due to minimal initial pressure loss
High dirt load
Quick and easy filter bag replacement – saving on labor costs and less downtime
Cost-effective – adapted to your system parameters
Minimal loss of process fluid
Reliable, consistent performance
Pressurized filtration system
Filter vessels and baskets

What is a micron? Liquid filtration involves the removal of contaminating particles in a liquid system. The filter class chosen for a specific application is usually determined by the size of the particle to be removed. Polluting particles are measured using the “micron” unit of measure.

A micron is a metric unit of measurement where one micron corresponds to one thousandth of a millimeter.
[1 micron (1μ) = 1/1000 mm] Or 1 micron (micrometer) = 1/1,000,000 of a meter.

Mesh vs. Micron
The old imperial standard system for measuring the ability of a woven filter media to remove contaminant particles was the mesh system. This system simply counted the number of threads or yarns per inch of woven media. Thus, a 100 mesh media has 100 threads per inch of media.
This system falls short because the actual window opening of a woven structure may vary as the diameter of the yarn varies. For example, a fabric with 50 meshes and a yarn diameter of 100 microns would have a window opening of 410 microns, while a fabric with 50 meshes and a yarn diameter of 200 microns would have a window opening of 310 microns.
However, the micron system attempts to measure an exact window opening for a woven medium and an exact particle size retention for a non-woven medium.

Visualizing a micron
A human red blood cell is 8 microns. An average human hair has a diameter of 50 microns. Most people cannot see anything smaller than 40 microns with the naked eye.
The following table covers the size of some common particles:
Microns (Range) Pollutant
0.3 – 0.4 Smoke, paint pigments
0.4 – 0.55 Bacteria
0.55 – 0.7 Lung damaging paint
0.7 – 1.0 Atmospheric dust
1.0 – 1.3 Moulds
1.6 – 2.2 Flour mill dust
3.0 – 4.0 Cement dust
4.0 – 5.5 Pulverized coal
5.5 – 7.0 Commercial dust
7.0 – 10.0 Pollen
10 – 75.0 Sludge 75- 1000 Sand


The micron measurement unit is used not only to measure the size of a contaminant particle, but also to measure the size of the openings in filter media, hence the micron rating of a media. This measurement system is more accurate when measuring woven filtration structures, such as monofilaments, than when measuring non-woven structures, such as felt.

Filter bag media Filtration media, whether woven or non-woven, are made from natural or artificial fibers. The development of synthetic fibers such as polyester, polypropylene, nylon, aramid, rayon, viscose, and polyethylene, has virtually eliminated the use of natural fiber media in liquid filtration. When selecting a media for a specific application, the “fiber content” can be critical as fibers withstand specific chemical and thermal environments.

Surface filtration Surface carriers remove contaminating particles at their surface. They are generally two-dimensional woven structures and are only as deep as the diameter of the yarn from which they are woven. They only capture particles larger than the window opening of their structure. The advantage of surface media is that they can be woven with great precision. Their disadvantage is that they offer a lower particle load or “dirt holding capacity” because they have little depth. As a result, they tend to silt up or “blind” more quickly than their “depth media” counterparts.

Not all surface media are woven. Some are composed primarily of matted fibers bonded together with heat or binders and are known as “spun-bonded” or “point bonded” structures. They are primarily used in multilayer applications as covers for bypass and transfer layers because of their low inherent strength property.

Depth Filtration
Depth media remove contaminant particles both at the surface and in the depth of the structure. They are usually of needle-felt or melt-blown, three-dimensional construction. This structure creates a tortuous path for particles to follow, which often results in particles with sizes smaller than the actual pore openings being captured.


High dirt holding capacity.
Higher void volume or pore volume
Ability to remove gelatinous particles
Ability to remove particles smaller than the average pore size opening
Long service life