Filter Press Cloth 15L: the open 25 micron grade for throughput and cake release

When the problem is not the fineness but the clock

Most filter cloth enquiries are about retention. This page is for the other case. The filtrate is fine, but the press takes too long. Chambers fill slowly, differential pressure climbs early, or too much cake stays on the fabric when the press opens.

For those situations the 15L is the answer in this range. As a high permeability filter press cloth it carries 15 ± 6 l·dm⁻²·min⁻¹, the highest documented air permeability of all the direct grades, five times the 3L and two and a half times the 6L.

One word about expectations before you order. A more open fabric can lower the resistance of the cloth. Whether the cycle gets shorter is decided by the cake. Once a load-bearing layer has formed, that layer sets the resistance and the fabric no longer does. With well draining suspensions the difference is clear. With strongly compressible cakes it is much smaller.

The construction behind the low fabric resistance

The 15L is the lightest and thinnest of the four direct cloths: 320 ± 40 g/m² and 0.5 mm. The 3L weighs almost twice as much and is almost twice as thick.

Add to that the most open thread grid in the family at 44 warp and 14 weft threads per centimetre, and a plain weave, the simplest and most regular construction, where warp and weft alternate over and under. The result is an even, clearly defined structure.

The yarn combines monofilament and multifilament. In construction terms that puts the 15L closer to the 6L than to the 7L, even though it shares its nominal rating with the 7L.

Poor cake release: what a calendered filter cloth can and cannot do

The fabric is calendered, that is, smoothed under pressure. A smoother face gives the cake fewer places to hold on to, and the monofilament content supports that, because smooth single strands trap less solid material between them than a pure multifilament yarn.

That makes the 15L the grade we suggest first when cake release is the complaint. We cannot promise good release. Whether a cake lets go is decided first of all by what it is made of, how much moisture is left in it and how compressible it is. A smooth fabric improves the starting position. It does not replace a change to the process.

If residues still stick, the right tool belongs with it, and that tool is not a metal scraper.

What the figure 15 ± 6 l·dm⁻²·min⁻¹ actually means

The tolerance is worth a moment. The band runs from 9 to 21, so the top end is more than double the bottom end. That is not unusual for openly built fabrics, but it shows how carefully a single number should be handled.

There is a second limit. The value is determined on dry air through flat fabric, and for the 3L and the 15L no test pressure is documented in the papers we hold. That restricts a direct comparison with the 6L figure at 200 Pa. A short cycle time cannot be derived from it. The question only becomes answerable through a comparison on the real medium.

Technical data for the 15L filter press cloth

15L or 7L: the decision in four lines

Common questions about the 15L filter cloth

The questions here are about throughput expectations and about the line between this grade and the 7L.

Does a high permeability filter cloth automatically shorten the cycle?

No. A more open fabric lowers the resistance of the cloth. As soon as the filter cake has built, the cake sets the resistance. With well draining suspensions the effect is clear, with strongly compressible cakes it is small.

What separates the 15L from the 7L?

The nominal rating is 25 micron for both. The 15L has a documented mono and multifilament construction in plain weave, 320 ± 40 g/m², 0.5 mm and 15 ± 6 l·dm⁻²·min⁻¹. Those values do not exist for the 7L.

Does higher permeability mean cloudier filtrate?

Not necessarily, but the possibility is there, above all in the start phase before the cake has formed. If filtrate quality is already marginal, move to a more open grade carefully.

What does the tolerance of plus minus 6 mean?

The documented value lies between 9 and 21 l·dm⁻²·min⁻¹. Bands like that are normal for openly built fabrics. For sizing, do not treat the mean as if it were an exact figure.

Does the 15L help with cakes that stick?

The calendered face and the monofilament content improve the starting position. Whether your cake releases also depends on its composition, its residual moisture and its compressibility. We do not give an assurance.

Is the 15L made as a head or end cloth?

Yes, like all five grades. For a quotation we need the plate size, the position in the plate pack, the inlet, the edge and the fixing method.