Polyester Felt Bag Filter

Name: Polyester Felt Bag Filter
Brand: Prosestim

Resistance up to 135 °C, 1–200 µm and High Efficiency in Oil Filtration

The polyester felt bag filter is a needle-punched felt depth filter that provides mechanical strength and high dirt-holding capacity at temperatures up to 135 °C.

Diameter

100–180 mm

Boy

230–810 mm

Micron Rating

1–200 µm

Max. Operating Temperature

135 °C (275 °F)

Polyester Felt Bag Filter

What Is a Polyester Felt Bag Filter?

Polyester felt is a nonwoven fabric produced by the needle-punched method. As liquid passes through it, this structure traps particles not only at the surface but throughout the depth of the filter fabric. This gives bag filters a higher dirt-holding capacity than many cartridge filters.

With dimensional stability that maintains its mechanical integrity at high operating temperatures, polyester felt gives long-lasting filtration in demanding liquid processes. In addition, its high mechanical strength and dimensional stability make it the choice for demanding processes that combine heavy particle loads, high flow and mechanical vibration. It is highly efficient in filtering oils and oily products, which is why hydraulic oils, lubricating oils and oil-containing process liquids are among its best applications. Paint and coating lines, hydraulic systems, automotive parts washing processes and chemical processing lines are this product’s most common applications.

Product Identity and Technical Summary

Polyester felt bag filters are made from 100% polyester fibres, free of binders and resins, by the needle-punched method. They offer a wide micron range from 1 µm to 200 µm and are used safely with liquids in the pH 4–9 range. Highly efficient in filtering oils and oily products, they are preferred on industrial, paint and coating, automotive and oil process lines.

The industrially stitched construction keeps the bag intact at operating temperatures up to 135 °C, while the thermo-mechanical surface finish reduces the release of loose fibres into the filtered line, contributing to a clear product output. For food applications, raw material suitability and documents are confirmed with our technical team.

Note: The values given are for standard production. Please consult our technical team for special application conditions.

Key Technical and Structural Features

Material: 100% pure polyester needle-punched felt; nonwoven depth fibre matrix.
Micron Rating: 1 µm · 5 µm · 10 µm
25 µm · 50 µm · 75 µm
100 µm · 150 µm · 200 µm
Max. Operating Temperature: 135 °C (275 °F) continuous operating temperature and thermal dimensional stability.
Recommended Change-Out Pressure: Bag replacement is recommended when the inlet–outlet pressure difference (ΔP) reaches 2–2.5 bar.
Seam Construction: 5-thread industrial stitching. Polyester felt bags are not made by ultrasonic welding; they are all stitched.
Chemical Compatibility (pH): Used safely in the pH 4–9 range; not recommended for liquids containing strong acids or strong bases.
Food Compatibility: For food applications, raw material suitability and documents are confirmed with our technical team.
Specific Gravity: High-density fibre structure of 1.38 g/cm³ with mechanical strength.
Binder Content: Pure mechanical needling with no binders, adhesives, silicone or resins.

Filtration Architecture and Working Principle

Polyester felt bag filters pass dirty liquid from the inside of the bag to the outside in a three-stage treatment process. First, coarse particles are retained on the inner surface, then finer particles in the depth of the felt; particles down to the selected micron rating are thus removed from the system.

Filtration takes place inside-out: dirty process liquid enters the bag; large particles are retained on the inner surface and finer particles in the depth of the felt. The filtered clean liquid collects in the space between the bag and the body and leaves through the outlet. The stainless support basket on the outside keeps the bag in shape at high differential pressures.

STEP 01

Surface Filtration

Dirty liquid enters the bag and meets the inner surface. Large particles above the specified micron threshold are retained in the inner layer of the bag and cannot pass the filter wall. This first filtration stage stops coarse contaminants from reaching the rest of the system, protecting pumps, pipelines and equipment from wear while reducing the load on the following filtration stages.

PROCESS BENEFIT Stops coarse contaminants before they reach equipment; protects pumps and pipelines from wear.

STEP 02

Depth Filtration

Smaller contaminants that get past the inner surface enter the fibre network of the polyester felt wall. As the liquid passes from inside to outside through this labyrinth structure, micro-particles are trapped deep in the fibres by mechanical entrapment, impaction and adsorption. The high mechanical strength of polyester fibre keeps the fibre structure intact even under heavy particle loads.

PROCESS BENEFIT Captures micro-particles invisible to the eye; helps maintain product purity and consistent process quality.

STEP 03

Differential Pressure

Contamination building up inside the bag gradually makes it harder for liquid to pass out through the filter surface. As the difference (ΔP) between internal and external pressure rises, the filter’s flow resistance increases. When the pressure difference reaches the set limit, it shows that the bag’s dirt-holding capacity is full and the bag filter must be replaced to maintain filtration performance.

PROCESS BENEFIT Replacing at the right time reduces unnecessary consumption and the risk of system failure; differential pressure monitoring makes maintenance planning easier.

Advantages of the Polyester Felt Bag Filter

The polyester felt structure retains particles not only at the surface but deep within the fibres. With high temperature resistance, high mechanical strength and a wide range of applications, polyester felt bag filters are widely used on industrial filtration lines.

Resistance to Oils and Fuels: Works stably with oils, fuels and industrial liquids in the pH 4–9 range; should not be used with strong acids and bases, ketones, esters or aggressive solvents.
Depth Filtration: Retains particles not only at the surface but throughout the thickness of the fabric.
Food Compatibility: For food applications, raw material suitability and documents are confirmed with our technical team.
High Flow Rate: Allows operation at high flow rates with low pressure loss.
Silicone-Free Production: No risk of cratering in paint and coating applications.
High Efficiency with Oily Products: The fibre structure provides high efficiency in filtering oils and oily products and a long service life on hydraulic and lubricating oil lines.
Easy Installation: Collar options compatible with standard housings.
High Temperature Resistance: Keeps its form under process conditions up to 135 °C; delivers reliable performance on high-temperature chemical and industrial lines.
High Mechanical Strength: Thanks to the high tensile strength of polyester fibres, the fibre structure largely keeps its form under heavy particle loads and mechanical stress.

Bag Diameter and Length Options

Polyester felt bag filters fit a wide range of housings with standard 100 mm and 180 mm diameter options. Four standard sizes, from short to long, meet different flow and volume requirements while offering direct compatibility with your existing system. For older or imported housings outside the standard sizes, custom production to sample is also available.

100 mm Diameter

Suitable for small-scale systems and laboratory-type filter housings.

180 mm Diameter

The industry-standard size and the most widely used size for high-flow systems.

Custom Manufacturing

Bags can be made to sample for older or imported special equipment.

180 × 430 mm: Standard Large Diameter • Short Length (~0.25 m² Filter Area)
180 × 810 mm: Standard Large Diameter • Long Length (~0.50 m² Filter Area • Most Common)
100 × 230 mm: Compact Small Diameter • Short Length (~0.08 m² Filter Area)
100 × 380 mm: Compact Small Diameter • Long Length (~0.14 m² Filter Area)

Custom-Size Production: Besides the standard housing sizes (Size 1, 2, 3, 4), bags can be made in lengths, diameters and collar types specific to your process or existing filter housing.

Micron Options and Precision

We offer a wide range from 1 micron to 200 microns according to the clarity your application requires. Efficiency in felt filters is nominal; the retention rate for particles of the stated micron rating is about 60–70%. The exact rate varies with the nature of the particles, the flow rate and the dirt load in the bag.

Micron (µm)	Precision Level	Typical Application
1–5	Very Fine	Final filtration, clarification
10–25	Fine	Fine chemicals, drinking water
50–75	Medium	Process water, pre-filtration
100–200	Coarse	Cooling towers, coarse particles

Collar Types and Adapters

A safe, leak-tight connection of the bag filter to the system starts with choosing the right collar. Six collar types, from PP rings to steel snap rings and from fabric flanges to drawstrings, can be selected according to the design of your existing housing, the operating pressure and the requirements of the chemical environment. If you are not sure which collar type fits your filter housing, send us a sample or photo and we will make an exact replica.

Critical Note: If you are not sure which collar type your filter has, you can send us a photo or ship a sample bag to our facility and ask us to produce an exact replica.

TECHNICAL ASSESSMENT BASED ON FIELD EXPERIENCE

Engineer's Note

The most common problem we see in the field with polyester felt bag filters is bypass caused by choosing the wrong collar type. Even if the filter medium has the right micron rating, filtration quality may fall short if the bag mouth does not seat fully on the housing’s sealing surface. The most important mistake made in the field is choosing a bag the same length as the basket. In that case the bag cannot sit fully on the bottom of the basket; as the pressure difference rises, the load falls not on the basket but on the bottom and seams of the bag, the bag tears, and the feedback from the field is that “the filter burst”. The bag should be chosen about 10 cm longer than the basket so that it sits on the bottom of the basket under pressure and the basket carries the load. When to choose it: in processes with a high particle load where the aim is to extend the filter change interval, a coarse + fine stage combination significantly extends the life of the main filter. When not to choose it: it should not be put into service with ketones, esters and chlorinated solvents or in acidic and alkaline environments outside the pH 4–9 range without confirming compatibility; PTFE filters should be chosen for these processes.

Caution In systems without differential pressure monitoring, bags may be changed too early or too late. Polyester felt can last longer than PP; however, temperature monitoring is recommended in systems running close to 135 °C, as excessive heat can cause a sudden drop in performance.

Application and Selection Criteria

Collar Type and Flange Fit: Choose the collar type based on a photo or sample of your current filter; relying on catalogue dimensions alone is not enough.
Bag and Basket Length: Choose a bag about 10 cm longer than the basket. A bag the same length as the basket cannot reach the bottom and will tear at the base under pressure.
Stage Combination: In processes with a high particle load, combining a coarse and a fine stage can significantly extend the life of the main filter.
Chemical Compatibility (pH): Polyester felt degrades outside the pH 4–9 range, with strong acids and bases and under prolonged hydrolysis conditions; it should not be put into service without confirming chemical compatibility.

Industry Applications

Bag filters suited to different process needs are used across a wide range of industrial applications to protect product quality, protect equipment and support production continuity.

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Performance Parameters

The field performance of a polyester felt bag filter is assessed on three main axes: its ability to meet the flow the line requires with low pressure loss, striking the right balance between micron precision, filtration surface area and service life, and keeping the risk of leakage at the bag-to-housing connection under control.

High Flow: Standard polyester felt media work with low pressure loss at high flow thanks to their open pore structure. The depth structure of needle-punched felt, combined with high dirt-holding capacity, extends the filter change interval and lowers operating costs.
Micron / Surface Area / Service Life Balance: Although bag life depends on the micron rating, it depends most on the filtration surface area. When enough surface area (the right bag length and number of bags) is chosen for the flow and solids load, the pressure difference rises more slowly; the right micron rating delivers the required clarity.
Sealing: With the right collar type and bag-to-housing fit, the risk of edge bypass (leakage) is minimised.

Filter Selection Technical Checklist

The wrong filter choice means early clogging, system failure and unnecessary cost. Choosing the right polyester felt bag filter requires ten critical parameters to be considered together, from the chemical nature of the fluid to the operating temperature and from the flow rate to the solids load. The checklist below is designed to help you make a fast, reliable choice on site and in technical discussions.

Chemical Nature of the Fluid: Polyester is suitable for liquids in the pH 4–9 range; for processes dominated by strong acids, strong bases or solvents, PP or PTFE should be considered.
Operating Temperature: If the liquid operating temperature is above 135 °C, high-temperature-resistant PTFE should be chosen.
Required Cleanliness Level: Choose the coarsest micron rating that will not harm the process; this significantly extends filter service life.
Flow Rate: The process flow rate in m³/h determines the right bag filter size and the number of bags/filter housings needed.
Viscosity: As liquid viscosity increases, pore resistance rises; size the micron rating and filter surface area accordingly.
Collar (Ring) Type: The bag filter collar must be mechanically compatible with the existing filter housing basket and sealing seat.
Solids Load and Contamination: If the particle and solids load in the liquid is high, larger filter housings or staged pre-filtration should be chosen.
Food & Hygiene Approvals: For applications in contact with food, verify the raw material's food suitability and the related documents.
Maximum Pressure & Strength: Check the maximum differential pressure (ΔP) limits that the filter body and bag can withstand before operation.
Ease of Change-Out & Ergonomics: A handle or loop on the bag shortens maintenance and change-out time and makes operation easier.

Points to Watch During Use

Getting maximum efficiency and life from a polyester felt bag filter depends on correct installation and operating practices. Sudden pressure fluctuations, incorrect installation or late replacement reduce filtration efficiency and put downstream equipment at risk. The points below have been compiled to prevent mistakes frequently seen in the field and to maintain system reliability.

Initial Start-Up: Avoid water hammer and sudden pressure surges when the filter is first put into service.
Correct Placement: The bag must be placed correctly in the filter basket and the housing without folds.
Timely Replacement: Replace the bag when the pressure difference (ΔP) between the inlet and outlet gauges reaches 2–2.5 bar. Exceeding this threshold can tear the bag and cause bypass.
Housing & Collar Fit: The collar type must match the sealing surface of the filter housing exactly.
Basket and Surface Check: If the old bag is deformed or bypassing at the edge, also check the basket and the seat surface.
Ring and Gasket Protection: The PP ring or snap ring must not be damaged during installation; avoid deformation caused by compression.
Washing & Reuse: Felt bags are single-use; washing and reusing them is not recommended.
Even Lid Tightening: Do not overtighten the housing lid; crushing the collar causes bypass and loss of sealing.

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Your Questions Answered

Frequently Asked Questions

At Prosestim, we are committed to answering your questions and providing technical support for our filtration solutions.

When should I replace the bag filter?

Replacement is generally recommended when the pressure difference between inlet and outlet reaches 2 to 2.5 bar.

Can polyester bags be washed and reused?

No. Because felt bags provide depth filtration, the dirt inside cannot be removed by washing, and the fibre structure breaks down, creating a risk of leakage.

Why does bag length matter?

The longer the bag, the larger the filtration area, giving higher flow and longer service life. The bag should also be chosen about 10 cm longer than the basket; a bag the same length as the basket cannot reach the bottom and may tear at the base under pressure.

Is polyester felt used for oil filtration?

Yes. Polyester felt is highly efficient in filtering oils and oily products; it is suitable for hydraulic oils, lubricating oils and oil-containing process liquids. All our polyester felt bags are stitched.

Do you have food-contact-compliant polyester filters?

Yes, we manufacture for food applications; contact our technical team for raw material suitability and documents.

What is the maximum temperature it can withstand?

Polyester felt bags withstand up to 135 °C. For higher temperatures, PTFE should be chosen.

Can it be used with acidic liquids?

Polyester is not resistant to strong acids and bases; it is used safely with liquids in the pH 4–9 range. For more acidic or alkaline liquids, consider PP felt, and PTFE at high temperatures.

Do you manufacture custom sizes?

Yes, we can manufacture to sample or technical drawing for all non-standard bag filter housings.

How do I know which micron rating to choose?

Our technical team will recommend the most suitable micron rating based on the type of contamination in your process and the clarity you need.

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