Round Cassette Filter Box for Air Ducts

A round cassette filter box (inline air filter housing) is a vital protective and purification component designed for supply, extract, and recirculation ventilation setups. Installed directly into round duct runs, this unit addresses the critical challenge of raw outdoor pollution by acting as the primary defense line for the system. The filter box efficiently traps coarse particulates such as road dust, airborne fluff, sand, pollen, and pet dander. By introducing this inline filtration node, building owners can prevent the premature fouling of expensive downstream HVAC assets—including inline fan impellers, electric or water duct heaters, and delicate heat recovery cores—thereby extending equipment operational lifespans and drastically reducing system cleaning overheads.

The robust rectangular enclosure is manufactured on automated industrial machinery from high-grade structural hot-dip galvanized sheet steel, grade DX51D, featuring a dense protective zinc passivation layer of Z275 (275 g/m²). This selection of raw materials provides exceptional casing rigidity and resistance against system static pressure loads. It safeguards the structure from developing localized rust spots or structural sagging, even when subjected to high-humidity environments, coastal air pockets, or extreme seasonal temperature fluctuations ranging from -40°C to +70°C.

Key Benefits of the Cassette Filter Box

• Tool-free inspection cover for effortless maintenance: The top access service hatch is secured with convenient ergonomic wing nuts. This enables building operators or homeowners to perform routine filter inspections and swap out clogged elements completely by hand, eliminating the need for specialized screwdrivers, nut drivers, or wrenches.
• Factory-fitted EPDM gaskets to eliminate sealant expenses: The round connection collars feature integrated double-lipped EPDM rubber seals. These elastomeric rings create a tight friction fit inside adjoining pipes, preserving calculated static pressure parameters and removing the need for messy liquid mastics, silicones, or external duct wrapping tapes.
• Precision-engineered internal guide tracks for bypass prevention: The internal tracking rails are tailored to match the exact dimensional depth of standard G3 or G4 coarse filtration media frames. This prevents the filter frame from tilting or vibrating under heavy airflow pressure, forcing all incoming air through the media and blocking unpurified air bypass.
• Sustainable inline architecture for long-term cost reduction: The rigid galvanized sheet steel enclosure is built to serve as a permanent part of the building infrastructure. When the filter material reaches its maximum dust-holding capacity (at a recommended final pressure drop of 250–450 Pa), only the low-cost inner disposable media insert needs replacement, bypassing the expense of purchasing a whole new housing.

Technical Specifications and Dimensional Matrix

The structural configurations, linear dimensional data, and collar manufacturing tolerances fully comply with European engineering standards EN 1505:2000 and EN 1506:2007 for round sheet metal ventilation networks. The double male connection ports are optimized for smooth inline sliding inside straight ventilation pipe tracks.

• Enclosure Structural Material: DX51D structural hot-dip galvanized steel (Z275 zinc mass coating)
• Metal Thickness Range: 0.5 mm to 1.0 mm scaled relative to nominal casing dimensions
• Compatible Media Classes: Pre-configured for coarse G3 or G4 pleated/panel cassette inserts
• Connection Interface Type: Double male nipple profile with factory-pressed EPDM gaskets
• Custom Engineering Configurations: Optional stainless steel outer casing versions are available upon request for facilities bound by strict sanitary-hygienic regulations

Assembly, Operational Placement, and Service Guidelines

Position the cassette filter box near the intake node of the air supply run, downstream of the external weather louver and motorized shut-off damper, but upstream of the inline fan or heating coils. Slide the male connection ports directly into straight round pipes until they sit flush against the pre-rolled mechanical stop beads. Secure the overlapping connection perimeter mechanically using blind structural rivets or self-tapping sheet metal screws. When choosing the installation site, ensure adequate clearance space is provided on the side of the removable service cover to allow smooth, unhindered withdrawal of the dirty filter element. Wrap all outer joint lines with high-adhesion aluminum tape to verify compliance with design system airtightness targets.