Industrial bag filters are classified primarily by cleaning mechanism rather than marketing label: pulse-jet, reverse-air, and shaker are the three dominant families in dry dust collection, with single-bag, multi-bag, and plastic variants used in liquid service [S2][S3].
Filtration media is the second axis of classification, with polyester (PE), polypropylene (PP), PTFE, Nomex, P84, fiberglass, and stainless steel selected for temperature, chemical resistance, and dust characteristics per the GB/T 6719 national standard for bag filters [S1][S7].
Cleaning method: the dominant classification axis
Pulse-jet bag filters use short bursts of compressed air (typically 0.4–0.6 MPa) injected through a venturi to dislodge the dust cake, allowing online cleaning without isolating the compartment from service [S2]. Pulse-jet systems dominate modern continuous-process plants because cleaning occurs in 60–100 ms pulses per row and the collector stays online, which is why most high-throughput cement, metal, and power-duty baghouses built since the 2000s are pulse-jet [S2].
Reverse-air bag filters stop forward gas flow in one compartment and pass low-pressure reverse air through the bags, producing gentler fabric stress and longer bag life on high-temperature or fragile felts (Nomex, fiberglass), at the cost of a larger footprint because one compartment is offline during each cleaning cycle [S2].
Shaker bag filters rely on mechanical vibration to drop the cake, which suits low-to-medium flow and intermittent duties, but cannot match pulse-jet on continuous operation and is generally specified for legacy or simpler service where online cleaning is not required [S2].
Configuration variants for liquid-service bag filters
Liquid-side bag filters split into single-bag (WF-1P1S through WF-1P6S, 1–6 bag positions) and multi-bag (2–24 bags, DN50–DN350 connections, 80–960 m³/h single-unit flow) configurations, with housings in SUS304/316/316L stainless steel or polypropylene for chemical resistance [S3].
Side-in/side-out and side-in/bottom-out flow patterns, plus top-entry designs, define how the filter is serviced; quick-opening clamps are standard for multi-bag units handling 960 m³/h at line pressures to 1.0 MPa, typical in food-and-beverable, RO pre-treatment, and electrocoat paint lines [S3].
Plastic (PP / UPVC) single-bag housings target acidic and alkaline duty where SS316 would still corrode, with seamless injection-molded shells rated for chemical service from pH 1–14 at temperatures typically to 60–80 °C depending on pressure rating [S3].
Filter media: material drives temperature and chemistry
Polyester (PE) filter bags handle continuous operating temperatures to roughly 130 °C with good abrasion resistance and are the workhorse for woodworking, grain, and general dust at near-neutral pH [S7].
Nomex (meta-aramid) felts operate continuously to about 200 °C and survive short excursions to 220 °C, making them the standard for asphalt plants and metal-melting furnace baghouses where sparks are routine [S1][S7].
P84 (polyimide) needles handle 240–260 °C continuous with excellent acidic gas tolerance, PTFE pushes continuous use to 260 °C and survives virtually all pH and moisture conditions, PPS sits at 190 °C with strong acid and hydrolysis resistance, and fiberglass is the baseline for 260–280 °C dry-gas service with mechanical fragility as the trade-off [S1][S7].
Air-side classification by efficiency grade
Synthetic multi-pocket bag filters in HVAC and cleanroom makeup air are classified to EN 779 grades M5, M6, F7, F8, and F9, with galvanized steel header frames and pocket counts typically 3–8 per filter module [S6].
Higher-grade pocket filters (F8–F9) target 90–95% efficiency on 0.4 µm particles in pharmaceutical and electronics cleanrooms, while M5–M6 grades are typical pre-filtration upstream of HEPA banks in commercial HVAC [S6].
How to select: a three-criteria comparison
For dust load, pulse-jet handles the highest inlet loads (up to 1000 g/m³ in cement kiln and metal-melting service), reverse-air sits in the middle, and shaker is restricted to low-loading batch duties [S2].
For gas temperature, reverse-air paired with fiberglass or PTFE media is the safe choice above 200 °C, pulse-jet with P84/PTFE/Nomex covers 130–260 °C, and shaker is limited to sub-130 °C service on PE or acrylic felts [S1][S2][S7].
Operating limits, failure modes, and common mistakes
The most common specification error is pairing PE felt with wet acid flue gas, which hydrolyzes PE and collapses bags in months; PPS or PTFE should be selected instead for sulfuric acid mist above dew point [S7].
Pulse-jet systems fail most often from wet compressed air in the manifold (water in the pulse valve freezes in winter, or carries oil that blinds the felt) and from over-pressure cleaning that mechanically punctures the felt; a 0.4–0.6 MPa dry-air supply with filtration to 1 µm and a regulator is baseline [S2].
Reverse-air and shaker systems share a different failure mode: compartment isolation valves leaking under differential pressure, which causes partial cleaning and uneven bag life across the house; valve seat inspection every 12 months is the working-engineer rule [S2].
Sourcing, standards, and cross-reference
The GB/T 6719 national standard defines the five-category Chinese classification system for bag filters, while EN 779 grades M5–F9 govern HVAC-side pocket filter efficiency, and ISO 16890 supersedes EN 779 for new European HVAC procurement [S1][S6].
For the broader field of how bag filters sit inside industrial filtration, the working engineer's map of industrial filter types and the spec-driven comparison of filter element media and ratings are the natural next reads. Closely related housings and strainers used upstream of bag filters are catalogued under precision filter and self-cleaning filter families.