Understanding filtration › 4. Diagnosing a cloth

CHAPTER 4.2

Filter press cloth failure: the classic causes

A cloth that tears prematurely is almost never "a bad cloth". More often than not, it tells you what is happening in the press. Here is how to read a failure and where to start the investigation.

Nicolas Ract · 8 min read · October 2026

Start by locating the failure

Before looking for an explanation, lay the used cloth flat and identify where it gave way. Five areas recur:

• The neck (the sleeve that passes through the plate's feed eye): tear at the base of the neck or around the eye.
• The sealing edge, where two plates close onto each other.
• The drainage surface: holes or thinned areas opposite the plate's pips or ribs.
• Seams and fastenings: broken threads, grommets or ties torn out.
• Widespread wear: cloth hardened, brittle or discoloured over its whole surface.

Also note the position of the plate in the pack (head, middle, tail) and whether several neighbouring cloths show the same failure.

Cause 1: pressure imbalance between two chambers

When two neighbouring chambers do not fill at the same rate, the cloth separating them is subjected to a pressure difference from one side to the other. It is then pressed against the plate, stretched, and the neck works on every cycle. A plate and cloth manufacturer explains that most plate damage comes from these out-of-balance pressures, and that the visible sign is a cake noticeably thicker in one chamber than in the next [1].

The causes it cites [1]:

• a feed eye blocked by leftover cake that did not discharge properly in the previous cycle;
• a feed passage "bridged" between two plates;
• a blocked filtrate outlet;
• an excessive feed rate;
• cloths of different permeabilities in the same pack, or chambers of different depths.

Cause 2: too abrupt a start-up

At the very start of the cycle, the cloth is clean and the cake does not yet exist: the cloth alone absorbs the flow and the pressure. Too rapid a pressure rise then puts heavy stress on the fabric and the seams, especially around the feed.

Field experience: a gradual increase in flow, then in pressure, at the start of each cycle spares the cloths. The exact settings depend on the pump and the product; they are validated by trial.

Cause 3: a damaged plate

The cloth follows the shape of the plate: every defect in the plate ends up marking the fabric. A sharp edge on the sealing edge, a broken pip, a hard deposit embedded in the drainage surface or a chipped feed eye cause very localised wear, always in the same place, on that particular plate.

Field experience: if the failure recurs in the same place on the same plate, examine the plate before ordering another cloth.

Cause 4: cake discharge

A sticky cake that is helped to fall with a metal scraper, a bar or a pointed tool is one of the most frequent sources of cuts. Poorly adjusted shakers and vibration systems also fatigue the fastenings.

Field experience: clean cuts, often at the bottom of the cloth, point to cake discharge. A cloth better suited to the product (smoother surface, calendered finish) can make discharge easier; this needs to be validated by trial.

Cause 5: washing

High-pressure washing is essential, but a nozzle held too close, at too steep an angle or for too long in the same place wears the fibres and eventually perforates the fabric. Incorrectly dosed chemical washes, for their part, attack it over its whole surface.

Cause 6: temperature and chemistry

Each fibre has its limits. As an order of magnitude, published charts give maximum continuous operating temperatures of around 80 to 90 °C for polypropylene, 100 to 110 °C for polyamide and 130 to 135 °C for polyester [2]. Beyond these, or in contact with a product the fibre does not tolerate well, the cloth hardens, becomes brittle and fails more or less everywhere rather than in one specific place.

Chemical resistance depends on the fibre, the concentration, the temperature and the exposure time: general charts [2] give an initial indication, but an immersion test or an on-site trial remains the only reliable check for a given process.

Cause 7: a poorly chosen or poorly fitted cloth

A cloth that is too large forms folds that wear; too small, it is under permanent tension and pulls on its fastenings. A cloth fitted askew leaks at the edge and works poorly at the neck. Finally, a highly abrasive sludge (minerals, residues) wears a fine fabric, or one with low abrasion resistance, more quickly: the choice of fabric construction matters as much as the choice of fibre.

From symptom to cause: a starting table

This table is meant to guide the investigation; it is not a rule. Several causes often combine.

What to record at every cloth change

Without a history, you replace cloths without ever finding the cause. One line per cloth is enough:

• the date, the plate number and its position in the pack;
• where the failure occurred, with a photo;
• the approximate number of cycles since fitting;
• everything that has changed since: product, temperature, setting, operator, washing.

After a few months, the dominant cause becomes apparent on its own. This is the subject of chapter 4.5, Keeping a service-life history. To examine removed cloths, see chapter 4.1.