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When is a precoat filter the right choice for fine coolant filtration?

As of November 2026

Reading time: 3 minutes

Brief Explanation

Precoat filtration is used to remove very fine solid particles from suitable coolants, such as grinding oils. A filter aid forms a layer on a support medium and traps particles as the coolant passes through. The layer is rebuilt after cleaning. Whether a precoat filter suits the application depends on the coolant, the solids load and the required filtrate quality.

How does precoat filtration work?

The process is divided into three phases that are repeated cyclically:

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Precoating: In a separate precoat tank, an agitator mixes the filter aid with clean process fluid. The mixture is circulated through the filter so that the filter aid forms an even layer on the filter candles.

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Filtration: Contaminated coolant flows through the precoat layer, which traps fine solid particles. The filtered coolant is returned to the process.

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Cleaning: The used precoat layer is removed along with the trapped particles. A fresh layer is then applied for the next filtration cycle.

The precoat layer is renewed in each filtration cycle. It captures fine particles that the support mesh alone may not reliably retain. For more details on the system design, see our precoat filter.

Where is precoat filtration used?

Typical applications include grinding, honing and lapping when the process generates fine particles and requires clean coolant. Clean coolant can help maintain surface quality and extend tool life. VDI 3397 Part 2, 2014 edition provides guidance on coolant maintenance. A precoat filter can also serve as a fine filtration stage in a central coolant filtration system that supplies multiple machines.

Precoat filter or belt filter?

 

KEP precoat filters

Belt filters, depending on the design

Filtration task

Removal of very fine solid particles using a precoat layer

Separation of fine to coarser solids, depending on the filter medium and design

Application Examples

Filter aid renewed after each cleaning cycle

Turning, milling, drilling, as well as grinding and honing

Filter media

Filter media that is replaced after cleaning

Filter fleece or reusable endless filter belt

Media

Oils and suitable aqueous solutions. Emulsions require a different filtration method.

Emulsions and oils, depending on the model and configuration

Limitations of the process

When the coolant contains coarse chips or a high solids load, a chip separator can reduce the load on downstream fine filtration. A belt filter may be sufficient if it already achieves the required filtrate quality. When sizing a precoat filter, match the filter aid and filtration cycles to the coolant and the solids load.

Frequently asked questions

When is a precoat filter a better choice than a belt filter?

A precoat filter may be suitable when very fine particles need to be removed and a belt filter cannot achieve the required filtrate quality. The more economical option depends on the coolant, the solids load and the required flow rate. 

A filter aid that is slurried onto the filter support prior to filtration and forms the actual, very fine filter layer there.

Often, yes—as a fine filtration stage in a partial flow. Whether this makes sense in a specific case depends on the process, available space, and required purity; we’ll clarify this during the plant design phase.

It describes the particle size at which the filter begins to reliably remove particles. Details and an explanation of the difference between nominal and absolute filtration are provided in the entry “Filter Fineness.”

Suitable solutions from KÖBO ECO>PROCESS

Filtration Technology

Precoat filter

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Filter Technology

Coolant filtration system

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KÖBO ECO>PROCESS Technical Editorial Team
Questions about this entry: Contact us

Contents

How does precoat filtration work?

Where is precoat filtration used?

Precoat filter or belt filter?

Limitations of the process

Related Terms

Precoat filtration

Precoat filter

Filter aid

Filter candles

Coolant

Belt filter

Filtration rating

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