Filter Press

A filter press is a batch (discontinuous) filtration device used for dewatering sludges. It consists of a series of plates covered with filter media, between which filter cakes form during pressing. GKD primarily supplies the filter cloths—the fabrics used in these filter presses. 

Operating principle: The filter press has a stack of filter plates covered with filter fabric or cloth. When the press closes, the plates are pressed tightly together, creating cavities (filter chambers) between every two plates, bounded by the filter cloths. The sludge to be filtered is pumped into these chambers. The liquid passes through the fabric into drainage channels (filtrate), while solids remain trapped between the cloths inside the chambers, forming filter cakes. Once the chamber is full (indicated by a pressure increase), the sludge feed stops. The press is then opened, the plates separated, and the solid cakes either drop out or are scraped off. 

The filter cloths (filter fabrics) must be very durable: they are subjected to high pressure every cycle (typically 5–30 bar) and must support the weight of the cake. At the same time, they must be fine enough to minimize solids passing into the filtrate (low turbidity). Typical materials include polypropylene, polyester, or polyamide fabrics; occasionally PTFE is used for aggressive media. The weave is often plain weave but frequently satin weave as well, since the smoother side helps the cake release more easily. 

To improve filtration performance and cake release, the sludge is often pretreated (flocculation, conditioning). Cake washing is also possible: after filling, washing liquid can be pumped through the cake to rinse out residual chemicals. Uniform flow through the filter fabric is critical here. 

Modern filter presses also use membrane plates, where flexible membranes squeeze the cake further after filling. The filter fabric requirements remain similar but must be elastic enough to accommodate membrane movement. 

Important: Filter cloths need regular cleaning or replacement because fine particles clog the pores (blinding). In-situ cleaning is done via high-pressure flushing or chemical cleaning (e.g., acid washing). Therefore, fabrics must be resistant to cleaning processes. 

For GKD, the main task is to provide fabrics that combine long service life, high permeability, and easy cleaning. Special surface finishes (calendered, coated) can help the cake release more easily or increase filtration fineness. 

Summary: The filter press is a classic filtration device for achieving high degrees of dewatering. The filter fabrics inside are key components—they determine throughput and separation quality. Continuous fabric improvements (material, weave, seam technology for attaching to plates) have steadily enhanced the performance and efficiency of filter presses over the years.