1. String-wound Filter Cartridges
True Depth Filtration
Sedifilt depth filters have revolutionized filtration with a superior technology that overcomes the limitations and drawbacks of other filters.
Superior Filtration Technology
Sedifilt filters have high structural integrity combined with a greater void volume, giving a lower pressure drop, much improved dirt holding capacity and efficiency compared to conventional filters. Sedifilt technology produces superior depth filters with increased filtration capacity, longer lifetime, and higher performance that reduce overall costs.
Superior filtration technology

2. Sedifilt string-wound filter cartridges: New developments in filter media
No media migration
Yarn consists of continuous filaments.
No short fibers to come loose and migrate.
The extruded media consists of continuous filaments of multi-lobal cross-section with numerous micro voids between each individual filament. These continuous filaments are then randomly oriented to each other, intermixed, looped and entwined into a non-round, highly stable, bulky yarn. See figure.
When this media is wound into a filter cartridge, each of the filaments continues, without a break, throughout the length of the yarn, making the cartridge free from any media migration problems. There are no short fibers that can come lose and migrate, a common problem with conventional string-wound filters.
Sedifilt media

3. No media migration No chemical leaching
Sedifilt string-wound filter cartridges: New developments in filter media
No media migration
No chemical leaching
No chemicals to leach out with new melt spinning and yarn forming process (patented).
No downstream foaming in filtrate.
100% pure polypropylene.
The process (patented) of making the new media begins with 100% pure polypropylene that is melt-spun (extruded) without the use of any chemicals.

4. No media migration No chemical leaching True graded density
Sedifilt string-wound filter cartridges: New developments in filter media
Illustration: Sedifilt graded density structure
Finer inner layer
Medium middle layer
Coarse outer layer
No media migration
No chemical leaching
True graded density
New winding technology.
Continuously controlled pitch, number of crossings and space between each strand of yarn.
Denser winding in inner layers, coarser winding in outer layers.
Consistent winding tension. high structural integrity, more consistent performance.
Through improved winding technology, the pitch, number of crossings and space between each strand of yarn is continuously varied and controlled from start to finish in making the cartridge. The inner layers of the yarns are wound close together and the space between yarns is gradually increased towards the outer layers, while the yarns remain locked together because of the random protruding loops. This winding technology gives improved true density grading, trapping coarser particles in the outer layers and finer particles in the inner layers. By maintaining the same winding tension, the structure has the same firmness throughout the depth of the cartridge, giving more consistent and better performance.

5. High dirt holding capacity
Sedifilt string-wound filter cartridges: New developments in filter media
Illustration: Sedifilt graded density structure
Finer inner layer
Medium middle layer
Coarse outer layer
No media migration
No chemical leaching
True graded density
High dirt holding capacity
Longer life as particles are trapped throughout the cross-section of the filter.
With the improved media, there are no typical diamond-shaped open spaces (a characteristic winding pattern of typical string-wound media) and the yarn media covers all the area. The liquid flows through the entire yarn structure and contaminant particles are forced to change direction as they proceed through the depth of the cartridge. The physics of flow is such that it becomes possible to trap particles smaller than the size of the complex pathways.

6. Multi-lobal cross section
Sedifilt string-wound filter cartridges: New developments in filter media
No media migration
No chemical leaching
True graded density
High dirt holding capacity
High bulk media Better performance
Media with high bulk, stable, three-dimensional random structure with multi-lobal cross section filaments.
Captures more particles compared to conventional filters.
Improved solid to void ratio gives higher flow rates with low pressure drop.
High bulk media
Multi-lobal cross section
The chemical-free continuous filaments are randomly oriented to each other, intermixed, looped and entwined into a non-round, highly stable, bulky yarn. See figure. The multi-lobal cross-section of filaments combined with the random yarn structure gives much improved solid to void ratio. This improved porosity provides for higher dirt holding capacity and reduced resistance to flow.

7. High dirt holding capacity High bulk media Better performance
Sedifilt string-wound filter cartridges: New developments in filter media
No media migration
No chemical leaching
True graded density
High dirt holding capacity
High bulk media Better performance
100% polypropylene
100% pure homopolymer polypropylene.
Wide chemical compatibility.
Excellent micro-organism resistance.
Environmentally safe.
Ease of disposal.
Incinerates to trace ash.
Sedifilt filters are made of 100% pure homopolymer polypropylene, a recognized environmentally safe and recyclable material for purity and ease of disposal. Polypropylene incinerates to trace ash with no hazardous volatiles.
A chemical compatibility guide is available in the brochure.

8. High dirt holding capacity High bulk media Better performance
Sedifilt string-wound filter cartridges: New developments in filter media
No media migration
No chemical leaching
True graded density
High dirt holding capacity
High bulk media Better performance
100% polypropylene
High structural stability No particle unloading
Firm, stable structure.
No shifting of media.
Improved resistance to particle unloading.
More consistent performance.
Excellent knife-edge sealing.
Each yarn traps the randomly protruding short loops of adjacent yarns resulting in a highly stable media structure wherein the yarns are locked in place and prevented from rolling or shifting to a side. The stable structure provides an excellent knife-edge sealing property to the cartridge. Under conditions of flow and pressure fluctuations, the new cartridge is more resistant to particle unloading.

9. High dirt holding capacity High bulk media Better performance
Sedifilt string-wound filter cartridges: New developments in filter media
No media migration
No chemical leaching
True graded density
High dirt holding capacity
High bulk media Better performance
100% polypropylene
High structural stability No particle unloading
Environmentally friendly
Environmentally friendly disposal.
Incinerates to trace ash.
No hazardous volatiles.
Sedifilt filters are made of polypropylene, a recognized environmentally safe and recyclable material for purity and ease of disposal. Polypropylene incinerates to trace ash with no hazardous volatiles for environmentally friendly disposal.

10. 5 micron, 10” polypropylene cartridge: Test results
Test Method: Retention Efficiency and Capacity per ASTM F795 Instrumentation: LD 400 SN
Fluid: Water Flow Rate: 3 gpm (US) Temperature: Ambient Contaminant: ISO Fine Test Dust
Shut Off delta P: 21 PSI
Test Method: Water at ambient temperature (25 °C.) Flow in US gallons per minute
Test Method: Efficiency and Capacity per ASTM F Instrumentation: LD 400 SN
Fluid: Water Flow Rate: 3 gpm (US) Temperature: Ambient Contaminant: ISO Fine Test Dust Shut Off delta P: 21 PSI
Test Results
Test results have shown that this new process provides up to twice the dirt holding capacity and filter life at equivalent competitive efficiencies, while reducing pressure drop up to half. All this translates into improved filtration performance and reduced costs.
Pressure drop vs. flow rate
Every filter cartridge has its pressure drop vs. flow rate curve, which is dependent on the permeability of the media. Compared to standard media, the new media has a higher permeability, which means a lower resistance to flow. The graphs show a pressure drop vs. flow rate curve for a 10 inch (2½ inch diameter) 5 micron nominal rated cartridge made from the new media.
Dirt holding capacity
Dirt holding capacity determines the useful life of a filter cartridge. This is determined by adding a specified amount of contaminant upstream at regular intervals and recording the differential pressure across the filter. The dirt holding capacity is then established by a limiting value of pressure drop (differential pressure) across the filter. The higher the amount of dirt held by the filter upon reaching the cut-off differential pressure, the longer the useful life of the filter. The graph shows the dirt holding capacity of cartridge made from the new media, which is much higher compared to standard filters.
Initial and final efficiency
Depth filter cartridges of fibrous media have a variable pore size, and thus no absolute rating. Instead they are given a nominal filter rating or a nominal efficiency figure expressed in terms of percentage retention by weight of a specified contaminant of given size. This applies over a range of particle sizes considered, down to the absolute cut-off size. At this point the number of emergent particles will be nil and the efficiency 100%. The graphs give the results for 5 micron rated cartridge made from new media. As a natural phenomena, the efficiency of a depth cartridge increases with the passage of time due to partial clogging of the voids.
When a new filter is put to use, initial efficiency is an important consideration to determine filtration suitability as the most amount of contaminants would pass through at this stage.
A final efficiency curve shows the amount of finer particles being filtered out before reaching the cut-off pressure.

11. Sedifilt string-wound filter cartridges: Economic benefits of Sedifilt
Increased filtration capacity
Higher dirt holding capacity
Longer lifetime
Fewer change outs
Reduced costs
Less labour requirement
Less equipment downtime
Lower inventory levels
5 micron 10"
Dirt holding capacity
Ordinary string-wound
30-55 gm
Sedifilt string-wound
108 gm
Sedifilt filters have high structural integrity combined with a greater void volume, giving a lower pressure drop, much improved dirt holding capacity and efficiency compared to conventional filters. Sedifilt technology produces superior depth filters with increased filtration capacity, longer lifetime, and higher performance that reduce overall costs.

12. Sedifilt string-wound filter cartridges: Filter cartridge range: End adapters and extended cores
Various types of cores, extended cores and end adapters are available.

13. Sedifilt string-wound filter cartridges: Filter cartridge range
The standard pure polypropylene cartridge is extractable-free and engineered for superior filtration performance. Available in up to 50 inch (1270 mm) length and 4.5 inch (115 mm) diameter.

14. Sedifilt string-wound filter cartridges: Applications
RO Pretreatment (SDI Reduction)
Drinking Water and Beverage Processing
Sea Water Desalination
Deep Well Injection
Gas Purification
Cooling Tower Water Filtration
Electronics and Electroplating
Industrial Process Water
Pharmaceutical & Healthcare
Chemical Industry
ED Automotive Paint
Photographic Solutions
Wastewater Disposal
And more …
Pure polypropylene Sedifilt filter cartridges are free from any extractables and contain no lubricants, wetting agents, emulsifiers, ant-oxidants or anti-static agents, etc. They are suitable for use in applications like RO Pretreatment (SDI Reduction), Drinking Water and Beverage Processing, Sea Water Desalination, Gas Purification, Electronics and Electroplating, Photographic Solutions, etc.
The standard pure polypropylene cartridge is extractable-free and engineered for superior filtration performance. Available in up to 50 inch (1270 mm) length and 4.5 inch (115 mm) diameter.

15. String-wound Filter Cartridges
Comparison with conventional media

16. Conventional media cross-section
Round cross-section
Fewer micro-voids
Lower dirt holding capacity
Higher resistance to flow
Conventional media cross-section
The short fibers used in making friction-spun yarn, melt blown or felt/paper media normally have a round cross-section. Conventional round cross section of individual fibers has fewer micro-voids giving lower dirt holding capacity and higher resistance to flow.

17. Sedifilt media cross-section
Multi-lobal cross-section
More micro-voids
Higher dirt holding capacity
Lower resistance to flow
Sedifilt media cross-section
The new media for string wound cartridges are made from continuous filaments with a multi-lobal cross-section. When this is combined with the yarn’s highly bulked structure, it provides for excellent solid to void ratio, giving lower pressure drop, improved dirt holding capacity and efficiency.

18. Comparison with conventional media: Conventional media vs
Comparison with conventional media: Conventional media vs. Sedifilt media
Sedifilt media has a higher void to solid ratio, giving higher flow rates, improved dirt holding capacity, and lower pressure drop.
Conventional media cross-section
Sedifilt media cross-section
The voids formed by a round cross-section fiber are fewer as compared to the spaces formed by multi-lobal cross-section filaments. Fewer micro voids mean higher resistance to flow and lower dirt holding capacity as illustrated above.

19. Conventional string-wound filter cartridges: Problems with conventional media
Media migration
Short fibers are not properly or fully locked into the main body.
Fibers tend to come loose and migrate into filtrate with flow of liquid and pressure surges.
Loose fiber ends protruding from the surface can be seen clearly in friction-spun yarn media.
Conventional string-wound filter cartridges
Polypropylene string wound cartridges, due to their inertness and wide range of chemical resistance, are among the most commonly used filters for reducing sediments and other suspended impurities in liquids and water. Traditionally these cartridges are made from ‘friction-spun’ yarns. Friction-spun yarns are a product of the standard textile yarn forming process.
Media migration
Despite their great popularity, these string wound cartridges have many major drawbacks. Friction-spun media comprise short fibers, usually about 50 to 75 mm in length. Some of the fibers get broken into even shorter lengths as they pass through the various mechanical textile processes of bale opening, carding, drawing and spinning. Many of these short fibers on the yarn’s surface are not properly or fully locked into the loosely twisted main body, resulting in media migration problem. Fibers on the surface of yarn tend to come loose with flow of liquid and pressure surges in the system.
Friction-spun yarn media

20. Media migration Chemical leaching
Conventional string-wound filter cartridges: Problems with conventional media
Media migration
Chemical leaching
Spin-finish chemicals (lubricants, surfactants, antioxidants, antistatic agents, emulsifiers, bactericides, etc.) leach out.
Evident as foaming in filtrate.
Washed media is never 100% ‘clean’.
Chemical leaching
In the standard textile yarn manufacturing process, by which polypropylene or other synthetic yarn media are made, a spin-finish has to be necessarily applied on the surface of the fibers. Spin-finish contains a number of chemicals like lubricants, surfactants, antioxidants, antistatic agents, emulsifiers, and bactericides, etc. Without the use of these chemicals, synthetic fibers cannot be converted into yarn media on textile machines. The quantity of these chemicals can vary from about 0.5% to as much as even 2% by weight of the filter media. Unless the media is pre-washed (though some residue will remain), these chemicals start to leach out and can be often observed as foaming in the filtrate. The leaching out of these chemicals can be detrimental for the filtrate as well as downstream treatments.
Friction-spun yarn media

21. Media migration Chemical leaching Particle unloading
Conventional string-wound filter cartridges: Problems with conventional media
Media migration
Chemical leaching
Particle unloading
Round cross-section media have unstable structure.
Under conditions of flow and pressure surges, unstable round yarns shift, giving rise to ‘tunneling’ effect and particle unloading.
Unstable structure of conventional cartridge of friction-spun yarn allows a paper clip to be pushed through the media.
Particle unloading
Friction-spun yarn media have a compact round cross-section. Cartridges made from these yarns do not form a stable structure, and when subjected to conditions of flow and pressure surges, these unstable round yarns shift, which gives rise to a ‘tunneling’ effect and particle unloading.
In string wound cartridges, different micron ratings are basically achieved by winding the yarn close together or with some gap. As the gap between the yarns is increased, the round yarns tend to roll or move to one side or the other. The liquid takes the least resistant path between the yarn gaps, rather than through the whole media, giving inconsistent filtration. As can be seen in the figure, a paper clip can be made to easily pass through a typical cartridge wound from friction-spun media with little pressure and effort. If a paper clip can pass through the filter, any contaminants can, too. Pushing in the paper clip has shifted the yarns to a side, which shows the unstable nature of the media.

22. Conventional cartridge of friction-spun media
Conventional string-wound filter cartridges: Problems with conventional media
Media migration
Chemical leaching
Particle unloading
Poor knife-edge sealing
Unstable edges cause seal by-pass problems.
Conventional cartridge of friction-spun media
Poor knife-edge sealing
Most filter housings use a ‘knife-edge’ sealing principle and unstable edges give poor sealing and cause by-pass problems.

23. Conventional melt-blown cartridges: Melt-blown media
Only Advantage:
Freedom from process chemicals
Disadvantages:
Tendency to collapse under moderate pressure differential
Requires supporting core
Very poor knife- edge sealing
Particle unloading
Melt-blown cartridges
Melt-blown filter cartridges were developed several years ago as a lower cost substitute for string wound cartridges. They are made using a one-step process in which high-velocity air blows molten polypropylene resin from an extruder die tip onto a take-up screen or a mandrel to form layers of self bonding fiber web. The only real advantage melt-blown cartridges have over conventional string-wound filters is freedom from process chemicals. These cartridges do not have a supporting core and tend to collapse under even moderate pressure differential. The figure shows the very poor knife-edge sealing ability of a melt blown cartridge – the edges can be easily separated giving poor sealing and cause by-pass problems.
Higher density and more compact melt-blown cartridges are also made for improved resistance to collapsing and better edge sealing. But this is achieved at the cost of much higher resistance to flow and decreased dirt holding capacity.
Melt-blown filter cartridge

24. Resin-bonded filter cartridges: Resin-bonded media
Disadvantages:
Higher cost
Limited chemical compatibility
Bonding agent compatibility problems
Poor density grading
Lower dirt holding capacity
Prone to media migration – media crumbles easily
Poor knife-edge sealing
Bonded filter cartridges
Bonded cartridges are usually of core-less construction and consist of resin bonded fibers of solid particles. A popular type is made from short cellulose fibers using phenols or melamine as the bonding agent. As these cartridges comprise more than one material, incompatibility can lead to ineffective filtration and costly process errors. The popularity of these cartridges is decreasing due to their relatively higher cost and suitability being mostly limited to viscous fluids. The dirt holding capacity of these filters is not good as density grading of the depth medium is poor. As such these cartridges are made with grooves cut on them to increase surface filtration area. See figure.
The structure of the cartridge does not have any ‘springiness’ and as such does not form a good knife-edge seal. The housings have to be specially designed to provide spring loading. Also the media crumbles easily and a paper pin can be pushed through it.
Resin-bonded filter cartridge

25. Pleated paper cartridges: Pleated paper media
Pinched pleat
Only Advantage:
Absolute ratings are possible
Disadvantages:
Consists of more than one material
Weak strength of thin paper media
Pleat pinch-off and pleat collapse problems
Collapsed pleat
Pleated paper cartridges
They are fabricated in pleated form for extended area using filter sheet or a thin fibrous felt. These cartridges essentially work on the principle of surface filtration but some depth filtration also takes place, which can have a profound effect on the characteristic and life of the filter. When surface type filters are exposed to the flow of contaminated fluid, some of the pores become partially blocked by small hard particles as well as by partial intrusion of soft deformable particles. These particles can form a slime or gel that can completely clog a filter and a ‘cake’ or bed of trapped particles starts to build on the surface of the medium as operating time continues. As such these filters are suitable only in situations where the incoming water or fluid is relatively clean. A major drawback of pleated paper cartridges is the weak strength of the thin media. The edges of the pleated media are prone to abrasion by hard particles like sand, etc. leading to complete filtration failure. See figure. A paper clip can be easily pushed through the thin weak media.
Another major problem with pleated paper cartridges is pleat pinch-off and pleat collapse. As the liquid flows from an outside-in direction and pressure differential rises, the pleats begin to pinch-off and collapse, drastically reducing the life of the cartridge. See figure.
Pleated paper cartridge

26. Comparison of surface and depth filtration
Direct interception
Particles larger in size than the pores deposit on surface of media
Numerous tortuous flow passages
Direct interception and dirt retention within depth of media
Complex mixture of mechanisms
Surface filtration (straining)
Surface filtration or straining works largely by direction interception. Particles deposit on the surface of a medium, provided they are larger in size than the pores of the mechanism, as shown schematically in the figure.
When surface filter are exposed to the flow of contaminated fluid, certain effects start to take place almost immediately;
Finer filtration: a gradual reduction in the effective pore size of the medium, as some of the pores become partially blocked by particles, so the filter starts to become ‘finer,’ that is more efficient in removing fine particles.
Clogging: however, the partial intrusion of soft, deformable particles into the pores, acting under the forces generated by fluid flow can block the pores causing the filter to clog.
Cake formation: a ‘cake’ or bed (thick layer) of trapped particles starts to build on the surface of the medium, itself forming a filter.
Depth filtration
The mechanism of depth filtration is very complex. The path through the filter is much longer and random, providing greater possibility for both direct interception and dirt retention. Larger particles will tend to be trapped in the surface layers, with the finer particles trapped by succeeding layers.
The depth filtration mechanism continues within the depth of the medium, at any point where a flow channel narrows down to be smaller than the size of solid particles. Particles are trapped within the depth of the medium, even though they can be smaller than the flow channels. This involves a complex mixture of mechanisms. Particles are first bought into contact with the channel walls (or very close to them) by inertial or hydraulic forces or by Brownian (molecular) movement). They then become attached to the walls, or to each other, by van der Waals and other surface forces.
The Sedifilt graded density structure consists of numerous tortuous flow-passages or pores in which the particles are trapped and held by the mechanisms described above.

27. String-wound Filter Cartridges
Increased filtration capacity
Higher performance
Reduced costs
Longer lifetime
String-wound Filter Cartridges
True Depth Filtration
Sedifilt depth filters have revolutionized filtration with a superior technology that overcomes the limitations and drawbacks of other filters.
Superior Filtration Technology
Sedifilt technology produces superior depth filters with increased filtration capacity, longer lifetime, and higher performance that reduce overall costs.
Superior filtration technology