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A depth stack filter cartridge is built by stacking individual “cells” on top of each other. Each cell is typically made from two circular discs of depth filter media bonded along the outside rim. Depending on the requirements, a cartridge can contain anywhere from 5 to 17 of these cells.
The media itself is usually a composite material, most commonly made from cellulose fibers combined with inorganic filter aids like diatomaceous earth. This creates a highly porous, rigid structure.
The filtration process in a depth stack cartridge relies on a combination of mechanisms.
The flow is typically from the outside to the inside. The fluid enters the cartridge housing, passes through the outer surface of the stacked discs, travels through the depth of the filter media, and then flows into a central channel where the clean filtrate is collected.
Mechanical Entrapment: Particles get physically trapped within the maze of pores and fibers as they travel through the media’s thickness. This is the primary mechanism of a depth filter.
Depth Filtration: The media has a gradient pore structure. The outer layers are more open to capture larger particles, while the inner layers are tighter to capture finer contaminants. This distributes the contaminant load throughout the entire cartridge, preventing premature surface blinding and extending its life.
Electrokinetic Adsorption: Many advanced depth stack filters use media that is chemically treated to have a positive charge. This allows them to capture very fine, negatively charged particles (like colloids, bacteria, and some organic contaminants) through electrostatic attraction, a process that goes beyond simple mechanical sieving.
The basic design can be modified for specific needs.
“Lenticular” Shape: This refers to the lens-like shape of the individual discs, which is a common term for this type of cartridge.
Double-Layer Designs: Some advanced cartridges use cells with two layers of filter media with different retention ratings. This allows for two-step filtration (coarse then fine) within a single cartridge.
Double Separator Concept: Many designs incorporate a separator between the media sheets to provide structural support and ensure an optimal flow path.
Backflushing Capability: Not all depth stack filters can be backflushed. Backflushing can damage the filter sheets and cause micro-cracks. However, some newer designs, like the Eaton BECODISC R+, are engineered with a honeycomb fabric between cells to allow for backflushing, extending the cartridge’s service life.
Enclosed System: They are designed to be installed in a fully enclosed housing. This is a significant advantage over traditional plate-and-frame filters, as it creates a drip-free, hygienic, and leak-proof system.
Depth stack filter cartridges are used in many industries where high-purity liquid filtration is required. Common applications include:
Food and Beverage: Filtration of wine, beer, juice, and other beverages.
Pharmaceutical and Biotech: Clarification of APIs (active pharmaceutical ingredients), vaccines, and biopharmaceutical fluids.
Fine Chemicals: Filtration of resins, solvents, and other chemical products.
A depth stack filter cartridge works by combining mechanical entrapment with electrokinetic adsorption within a thick, porous media. Its stacked disc construction, gradient pore structure, and ability to filter throughout its entire depth give it a high dirt-holding capacity and make it an effective and reliable solution for critical liquid clarification applications.
