How to choose the right filter insert: wound vs. washable SX insert

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How to Choose the Right Filter Insert: Wound vs. Washable SX Insert

The filter insert is the heart of every water filter. You may have a quality housing, properly dimensioned piping, and precise installation – but if you have the wrong insert, the entire system will either quickly fail or give you a false sense of security. In practice, we see dozens of customer cases every year where people have installed a cheap wound insert where a washable one was needed, or vice versa – they have used a washable SX insert with too coarse a filtration level where fine mechanical filtration was actually required. The result: clogged pumps, pressure drops, reduced equipment lifespan, or in the worst case, mud and sand in the tap water.

This article will walk you through everything you need to know about the difference between wound and washable SX inserts – from basic structural differences, through specific real-life scenarios, to a decision-making process that you can save and refer back to at any time.

What is a filter insert and how it works

A filter insert (in English: filter cartridge) is a consumable or reusable element placed in a filter housing. Water enters the housing from the outside of the insert, passes through its filter material, where solid impurities are trapped, and exits the filter cleaned through the hollow center. The whole principle is simple – the game is played on the filter material and pore size.

When we talk about mechanical filtration, we mean filtration of solid particles – sand, mud, rust flakes, organic residues, algal fibers. This is not chemical or biological filtration – that is handled by other stages (activated carbon, UV lamps, softeners). Mechanical filtration is always the first step and without it, other filters lose their meaning – they get clogged too quickly or simply do not work properly.

In the category Water Filters, you will find both types – wound and washable SX inserts, as well as the housings into which they are inserted. In order to know what to choose, you must know the difference in their construction, materials, and clogging behavior.

Wound (wound) filter insert – construction and properties

A wound insert is made of fiber wound in a spiral around a hollow central core. The fiber can be polypropylene (PP), glass, or cotton – each material has slightly different properties, but the principle is the same: the tighter the fiber is wound, the smaller the filter pore. The layers are not uniformly tightly wound throughout the entire thickness of the insert. The outer layers are a bit sparse (coarse pre-filtration), while the inner layers are tightly wound (fine filtration). This is called gradient (stepped) filtration.

The advantage of the gradient structure is that the insert has a higher capacity – for the same size, it can hold more impurities before the pressure drop (pressure drop before and after the filter) reaches an alarming level. Coarse impurities are trapped in the outer layers, fine impurities penetrate deeper and are retained in the inner, more tightly wound layers.

Typical filtration fineness of wound inserts: 1 µm, 5 µm, 10 µm, 20 µm, 50 µm. For well water conditions, the most commonly used is wound insert 10 µm – it captures fine mud, silt, and small organic particles, while still not acting as a too quickly clogging barrier for normally turbid well water.

When Wound Cartridges Excel and When They Fail

A wound cartridge is excellent where the water is not extremely turbid, or where municipal water supply is used and filtration serves only as an additional safety layer. In these conditions, it can last several months, sometimes up to half a year without replacement, until the pressure drop becomes noticeable.

Problems arise when the water has high turbidity or a lot of sediment — for example, with well water in the garden, surface water, or after a pipe break when silt gets into the system. In such cases, a wound cartridge clogs much faster — sometimes within days or weeks. And since it cannot be rinsed (the fiber deforms, tears, and loses its structure), you have to throw it away and buy a new one. This is costly and ecologically inefficient.

Another issue: a wound cartridge cannot be easily visually assessed. It may look relatively clean from the outside, but the inner layers are clogged. The customer thinks the cartridge is still working, but the pressure is dropping. That is why we always recommend having pressure gauges before and after the filter — pressure drop is the only reliable indicator of the cartridge's condition.

Washable SX Cartridge – Construction and Benefits

SX cartridges (the designation comes from the manufacturer Atlas Filtri, referring to a series of filtered elements made of solid polypropylene) are structurally completely different from wound cartridges. Instead of fiber, the filtering element is made of solid polypropylene discs (lamellae) stacked on top of each other around a central tube. The space between the lamellae forms the filtration opening — typically 50 µm or 100 µm for common well applications.

When water passes through the SX cartridge, solid impurities are trapped in the gaps between the lamellae and on the surface of the cartridge. Key property: the lamellae are solid and rigid, and when rinsed with water (under pressure or manually), the impurities are released and the cartridge regains its original functionality. This is a fundamental difference from a wound cartridge — you do not have to replace the SX cartridge every month.

For well conditions, a typical washable SX cartridge 50 µm is used. Fifty microns is an ideal filtration level for most well water — it captures sand, coarser silt, and larger organic particles. Finer sediment (under 50 µm) is addressed in a further filtration stage, for example, a wound cartridge 10 µm installed after the SX cartridge — but we will get to that later.

Material and Durability of SX Cartridges

Polypropylene is chemically inert and resistant to most common substances in drinking and well water. It can handle pH levels between 2–12 and temperatures up to 60 °C (in standard water supply applications, temperatures rarely exceed 20–25 °C, so this is not a limiting factor). SX cartridges do not absorb impurities into their structure like fiber — impurities remain on the surface, which makes cleaning easier.

The lifespan of an SX cartridge with proper maintenance is 2–5 years, sometimes even longer. Compare this to a wound cartridge, which you replace every 1–3 months in a turbid well water source. The economic difference over 5 years is significant — the SX cartridge pays for itself very quickly.

Filtration Fineness: 10 µm, 50 µm, 120 µm – Where They Fit

Microns (µm) are a key parameter when choosing a cartridge. The number indicates the minimum size of the particle the cartridge will capture. The smaller the number, the finer the filtration — and the faster the clogging.

In practice, we encounter these typical scenarios:

120 µm: Coarse pre-filtration, typically before the pump. It captures sand, stones, and coarse sediment. It protects the pump impeller from mechanical damage. An example is the sand separator filter 1" 120–130 µm — it is mounted directly on the pump suction outlet, not in the pressure system after the pump.
50 µm: Typical filtration level for washable SX cartridges in well systems. It captures sand, coarser silt, and sludge particles. It is used as the first stage in a filtration setup after the pump — ideally in combination with a SENIOR filter or a similar housing.
10 µm: Fine sediment filtration with a wound cartridge. It captures fine silt, sludge, and organic fibers. Typically the second stage after the SX 50 µm cartridge, or a standalone cartridge where the water is relatively clean but slightly turbid with fine sediment.
5 µm and finer: Prefiltration before RO membranes, UV lamps, or other sensitive equipment. In well applications, as a standalone stage, generally not suitable — it clogs too quickly.

A detailed comparison of filtration levels can be found in the article Mechanical water filtration: comparison of 10, 50, and 120 microns cartridges in the Knowledge Center.

Filter housing: MONO vs. DUO – relation to insert selection

The type of housing directly influences which combination of inserts you can use. If you have Filter SENIOR 10" MONO with 1" connection, you have only one housing – meaning one filtration stage. You must decide whether to install an SX washable insert or a wound insert. For a well with noticeable turbidity and sand, a MONO filter with an SX insert of 50 µm is a good start, but not the end – fine mud still passes through.

If you choose Atlas Filtri Senior 10" DUO 1" – a dual filter for SX inserts, you get two housings in one compact body. This allows you to connect two filtration stages in series – for example, an SX 50 µm insert in the first housing and a wound 10 µm insert in the second housing. Result: excellent combined filtration, with the SX insert protecting the wound insert from rapid clogging. A wound insert of 10 µm will last much longer if an SX 50 µm insert is used as the primary barrier.

We discuss the MONO vs. DUO filter issue in more detail in the article What filtration do I need: MONO vs. DUO filter – difference and when to use which in the Knowledge Center.

Decision-making process: how to choose the right insert for your specific case

Based on our experience in practical applications, we have created a simple decision-making process. Answer these questions in turn:

Step 1: Where does the water come from?

City water supply vs. private well is the first and most important distinction. City water is pre-filtered, microbiologically treated, and sediment is minimal. In such cases, a wound insert with a long replacement interval is usually sufficient – for example, a 25–50 µm wound insert that you replace every 6–12 months. Well water is a completely different situation – sediment, sand, mud, biology, seasonal changes in turbidity after rain. In this case, you need an SX washable insert as a base.

Step 2: What is the visual condition of the water?

If you can see visible turbidity, sand at the bottom of a glass, rainbow film (oil substances), or smell – we are talking about heavily contaminated water. A wound insert is not sufficient as a single stage here, because it would clog too quickly. The basis is an SX 50 µm insert, possibly supplemented by additional stages (activated carbon, UV lamp). If the water is visually clean, but you are concerned about fine sediment (mud after rain), you can try a wound 10 µm insert – but be prepared to replace it every 1–3 months.

Step 3: What is the frequency and willingness to clean the filter?

This is a psychological, not a technical question – but it is crucial in practice. An SX washable insert requires regular cleaning (every 1–4 months depending on turbidity). Cleaning takes 5–10 minutes: you remove the housing, take out the insert, rinse it under pressure, and put it back. It is a simple service, but you must think about it and perform it. If this is not feasible for various reasons (weekend cottage, rental, elderly owner), a wound insert may be a more practical choice – anyone who can use a screwdriver can replace it.

Step 4: What is the economics of your application?

A disposable wound insert typically costs 3–8 € per piece. With monthly replacement for well water, this is 36–96 € per year – just for inserts, without labor or waste. An SX insert costs more initially (15–30 €), but with regular cleaning, it can last 2–5 years. Savings over 5 years in such conditions are 100–400 €, which is a significant difference.

Step 5: What is the required filtration fineness?

If you need to filter below 25 µm (for example, before a softener or UV lamp), SX inserts with such fine filtration are not commonly available. The SX series typically ranges from 25 to 500 µm, with 50 µm being the most common. For fine filtration below 25 µm, you must use a wound insert – there is no alternative.

Practical examples from customer practice

Example 1: Cottage with a well and garden pump

The customer had a submersible pump in an 8-meter deep well with concrete rings and sandy soil around. In summer months, water was intensively pumped for garden irrigation, shower, and toilet. In the first year, he had only a wound insert of 10 µm in the MONO filter SENIOR. After a heavy rain, the insert lasted only 3 weeks – the water brought fine silt and sand, clogging the insert. He spent more than 80 € annually on inserts.

Solution: He installed a washable SX insert of 50 µm in the housing. Cleaning every 6–8 weeks, the SX insert has served him for the third year without replacement. The filtration cost has decreased by more than 80 %.

Example 2: Family house on municipal water + fine filtration before water softener

The customer wanted to protect the water softener from possible impurities in the municipal water (sometimes turbid after water supply repairs). The softener requires filtration of at least 20–25 µm before the inlet. An SX insert of 50 µm is fine for turbidity, but for the softener, finer filtration is more suitable. Solution: A wound insert of 10 µm in a MONO housing before the softener. Municipal water is not turbid, and the customer changes the insert once a year – an investment of about 5–6 € per year. Efficient and no need for cleaning.

Example 3: House on a well with long outages and weekend use

The customer uses the house only on weekends. The well is shallow (4 m), and the water has visible silt after heavy rain. The customer does not want to change inserts every month or clean the filter regularly. Compromise: A DUO housing with SX 50 µm in the first stage and wound 25 µm in the second. The SX 50 µm protects the wound insert, so the wound 25 µm lasts 3–4 months instead of 3 weeks. The customer cleans the SX insert during each major visit (every 2–3 months). The system works, and service requirements are acceptable.

Example 4: Surface water from a stream for garden irrigation

The customer pumps water from a stream for vegetable garden irrigation. The water contains leaves, algae, coarse organic impurities, and sand. A wound insert of 10 µm would last only a few hours. Solution: As a first step, a coarse filter of 120–130 µm before the pump, and a washable SX 50 µm after the pump. Cleaning the SX insert every 2–3 weeks. A wound insert has no place in this system – it would be too expensive to operate.

Compatibility of inserts and housings: what to watch out for

Not every insert fits into every housing. Before purchasing an insert, check the following:

Insert size: The standard length is 10" (inches), which is about 25 cm. There are also 20" inserts – they do not fit into 10" housings. Always check the length.
Outer diameter of the insert: For SX inserts from Atlas Filtri, precise dimensions of the SX series apply. SX inserts from other manufacturers may not fit tightly into Atlas Filtri housings and water leakage around the insert may occur.
Connection diameter of the housing: A 1" housing has an internal thread of G1". Pipes and fittings must match this. More about this parameter in the article Filter insert size 10" and connection 1" – what do these parameters mean? in the Knowledge Center.
SX series: SX inserts are optimized for Atlas Filtri housings (SENIOR, ATLAS, etc.). If you have a different housing, check compatibility with the seller.

Proper installation and first start-up

Even with the correctly selected insert, improper installation can cause problems – water leakage around the seal, vibrations, or housing damage. The seal (O-ring) must be properly seated in the groove and can be greased with vaseline (food-grade vaseline, not machine oil). Tighten the housing manually + with a special wrench, not too much – the plastic may crack. A detailed installation procedure is available in the article Wall mounting of a water filter step by step: bracket, connection, sealing in the Knowledge Center.

At the first start-up, fill the system slowly – open the inlet valve slowly to avoid water hammer, which can damage the housing or insert. Let the first 2–3 liters of water drain, until the insert is "filtered through" – wound inserts may initially release a small amount of fibers, which is normal and disappears after a short flush.

Cleaning the SX insert – procedure and common mistakes

Cleaning the SX insert is simple, but you need to know how to do it. Basic procedure:

Close the water supply, open the valve after the filter to relieve pressure.
Unscrew the lower housing – using a special lever key or manually (most housings can be done manually).
Remove the SX insert – it may be covered with mud, brown sludge.
Rinse the insert under running water from the outside, use your fingers to gently move the lamellas to release dirt. You can use a soft sponge, not a wire brush.
Optionally, soak the insert for 15–30 minutes in water with a bit of citric acid (about 1 tablespoon per 1 liter of water) – this helps to dissolve lime deposits and algae.
Rinse with clean water, reinsert, tighten the housing, and open the water.

Most common mistake: customers clean the SX insert but then do not perform a pressure loss test. If after cleaning the pressure after the filter still does not allow normal flow, it may mean that the insert is clogged deep in the lamellas (by grease, biofilm) – in that case, a longer soaking time or replacement of the insert may help. For more on cleaning and replacement topics, see the article Washable inserts for well water: how and when to clean them and when to replace them in the Knowledge Centre.

Common mistakes when choosing an insert – summary

Too fine a wound insert for well water: A 5 µm insert in well water clogs extremely quickly. Start with a coarser one and adjust accordingly.
SX insert without regular cleaning: A washable insert that is not cleaned for 6 months does the same as a clogged wound insert – it blocks flow and overloads the pump.
Lack of a sediment filter before the pump: If you do not have a coarse pre-filtration on the suction side, fine inserts will clog even faster. Before investing in fine filtration, ensure coarse pump protection – see the sediment filter 1" 120–130 µm.
Wrong water flow direction: The housing must be connected with the inlet and outlet according to the marking. Reversed connection reduces filtration efficiency.
Ignoring the pressure gauge: Without pressure gauges before and after the filter, the customer cannot know when it is time to replace or clean the insert. The filter works, but either for too long (risk of letting through impurities) or too short (unnecessary costs).

Most frequently asked questions (FAQ)

Can I wash the washable SX insert indefinitely, or do I need to replace it sometimes?

SX inserts have a long, but not unlimited lifespan. With regular cleaning, they can last 2–5 years. Replacement is necessary when the lamellas lose stiffness, become deformed, or when the flow is still unsatisfactory even after thorough cleaning. Visual inspection of the lamellas during each cleaning is a good practice – if you see mechanical damage, cracks, or permanent discoloration deep in the lamellas, it is time for a replacement.

Can I wash and reuse a wound insert?

No. A wound insert is not designed for repeated cleaning. When trying to rinse it under pressure, the fiber deforms, tears, or loses its gradient structure. The result: the insert may look cleaner, but its filtration ability is compromised – it may let through impurities that it would normally catch. A wound insert is a single-use consumable.

What is the difference between an SX insert of 50 µm and a wound insert of 10 µm in terms of captured impurities?

SX 50 µm captures sand, coarser mud, and particles larger than 0.05 mm. Wound 10 µm captures fine mud, fine organic fibers, and particles larger than 0.01 mm. In practice, this means that SX 50 µm is a coarser pre-filter stage, and wound 10 µm is a finer polishing stage. The ideal combination is to connect both in sequence: SX 50 µm protects the wound 10 µm and extends its lifespan.

I have a well, the water looks clean. Do I need a filter at all?

Yes, even if the water looks visually clean. Mechanical impurities such as fine sand or rust particles often become apparent only after some time – through worn seals in appliances, clogged aerators, or damaged membranes in pressure tanks – not immediately visible water turbidity. A filter also protects all downstream devices (softener, heater, washing machine), whose repair or replacement due to deposits costs incomparably more than the filter and its inserts. Therefore, we recommend at least a basic sediment filter as a safeguard, even with visually clean water.

Do you have a question on this topic?

Not sure or dealing with a specific situation in your household? Write to us – we are happy to help.