Possible causes: Acute overload due to extreme dust ingress, incorrect cleaning parameters, irreversible clogging (blinding) of the medium, or an excessive air volume flow that exceeds the system's capacity.
Solutions: Check cleaning (operating pressure in the pressure tank depending on the medium 4-6 bar, impulse time depending on the medium 0.1 – 0.35 s), if necessary switch to Delta P cleaning to promote filter cake build-up and prevent deep storage, change filter medium (for very fine, sticky dusts, a change to special coatings may be necessary, for pleated media, reduce the pleat depth if necessary), control volume flow (if the actual volume flow is far above the design, this leads to high filter surface load and wear of the filter media), if necessary, the filter surface must be enlarged or the volume flow reduced.
Possible causes: Mechanical defect in the filter medium (tear, hole), inadequately secured element on the perforated plate (bypass), check volume flow (if the actual volume flow is far below the design, this leads to very low filter surface loading and barely measurable differential pressure)
Solutions: Check filter paper for dust traces, visually inspect the perforated plate for correct seating of filter elements and seals, examine filter media for damage and replace defective elements, if necessary increase volume flow (reduce constrictions or install bypasses).
Possible causes: The internal valve membrane is torn, the upstream solenoid valve (pilot valve) is faulty or blocked by dirt particles in the compressed air and no longer closes.
Solutions: Depressurise the compressed air tank, open the affected valve, check the diaphragm and spring for breaks and clean them or install the repair kit (diaphragm kit), replace the solenoid valve if necessary.
Possible causes: Too frequent cleaning (continuous pulsing) causes deep penetration of particles into the filter medium, abrasive or oily/greasy dusts.,
Solutions: Extend cleaning intervals or switch to delta p-dependent control, for abrasive fine dusts use polypropylene filter media, for oil-/grease-containing dusts switch to oleophobic filter media.
Possible causes: The seal on the filter plate or filter cartridge is missing or damaged, incorrect installation of the filter element, fabric too coarse for the fine dust present (conditioning failure), too frequent cleaning (continuous pulsing) prevents the formation of a protective filter cake, fine particles pass through the medium instead of being trapped by the filter cake.
Solutions: check seals and correct installation of filter media, switch to filter media with a PTFE membrane or solid body (Sinbran) for fine dust, extend cleaning intervals, or switch to Delta p-dependent control.
Possible causes: Dropping below the dew point in the filter housing (condensation formation), wet or oily compressed air from the compressor network in combination with hygroscopic dusts.
Solutions: Insulate or heat the filter housing, check the compressed air system's water separator and refrigerant dryer, use media with a PTFE membrane or oleophobic treatment for sticky dusts.
Possible causes: Residual dust remaining in the housing cools down during downtime, attracts moisture and settles on the elements as a sticky film.
Solutions: Activate post-cleaning phase (after-cleaning cycle). After the main fan is switched off, the cleaning process must continue to run automatically for 10–15 minutes while stationary, in order to completely discharge the dust into the hopper.
Possible causes: The tank volume of the compressed air reservoir is too small, the air supply line to the pressure tank is undersized, so that air cannot flow in fast enough, the impulse time is set incorrectly (too long)
Solutions: Enlarge the cross-section of the compressed air supply line, install a larger pressure tank, correct the pulse time (pulse time 0.1 – 0.35s depending on the medium).
Possible causes: The operating pressure in the compressed air tank is too low, the valve opens too slowly due to a defect, or the blow pipe is misaligned and does not hit the element opening centrally.
Solutions: Set the pressure regulator to the set point (usually 4–6 bar), check the alignment of the blow pipe with the filter inlets, and check the diaphragm valve and solenoid valve.
Possible causes: The downstream discharge unit (rotary vane feeder, screw conveyor or flap) is blocked, defective or overloaded, material clumping in the hopper and not feeding down sufficiently.
Solution: Stop discharge components and remove mechanical blockages, retro-fit a fill-level sensor in the hopper to prevent overloading early on, retro-fit knockers or vibratory pads.
Possible causes: The flushing pressure is too low; the filter element is blocked.
Solutions: Check the cleaning pressure at the pressure tank (4–6 bar depending on the medium); check the filter elements.
Possible causes: Abrasive dust strikes the filter media directly at too high an inlet velocity, or the support baskets have sharp edges or are damaged
Solutions: Fit baffle plates or a deflector in the raw gas inlet of the filter to redirect the air flow; check the support baskets and replace them if damaged.
Possible causes: The internal support frames are incorrectly dimensioned or damaged.
Solution: Check correct fit of basket and filter medium, check support frame for damage.
Possible causes: Use of pleated elements with sticky, fibrous, or very wet dusts. The narrow pleat spacing leads to mechanical bridging.
Solutions: Conversion of the filter to media with a larger pleat spacing, possibly filter bags or sintered elements (Sinbran).
Possible causes: Chemical reactions in the dust cake due to incomplete drying or falling below the dew point.
Solution: Increase process temperature, add thermal insulation to the filter housing, and if necessary, electrically heat it.
Possible causes: No power supply to the filter control unit, fault on the circuit board, main compressed air supply to the system is shut off.
Solutions: Check power supply and fuses for the control system, measure output signals to the valves, check the main shut-off valve on the compressed air line.
Possible causes: Missing or faulty earthing of the filter elements.
Solutions: Use exclusively antistatic filter media with a woven-in guide, Ensure that the grounding strands have metallic contact with the earthed perforated plate.
Possible causes: The filter is operated with excessively high negative or positive pressure, exceeding the static design of the housing.
Solutions: Immediately stop the plant, install safety valves, rupture discs or pressure relief devices, and, if necessary, reduce the operating pressure.
Possible causes: Deformed slot plate, missing filter media fastenings, damaged filter media support.
Solution: Check mounting plate for deformation, check fasteners, replace damaged elements (Caution: overtightening filter fasteners can damage filter elements!)
Cause: The pickup speed at the extraction points is too low, the extraction pipes are blocked
Solution: Check lines on flaps/throttles and open if necessary, check piping system for deposits, reduce filter differential pressure (e.g. by cleaning or changing filter media) to increase volumetric flow.
The actual filter is not the fabric (the needle-punched felt), but the dust that accumulates on it – the filter cake. A new or freshly cleaned bag has relatively large pores. Fine dust would simply pass straight through. Only when the first layers of dust build up on top of one another do they mechanically block the pores. It is only thanks to the cake that the separation efficiency rises to almost 100 %.
Rule of.
The residual cake (or base layer) is the very first dust layer that adheres directly to the fibres of the filter medium. With an optimally adjusted jet pulse cleaning system, the pressure pulse only removes the excess, heavy surface cake. The residual cake deliberately remains on the fabric as a protective skin, ensuring that filter performance is immediately high again after the cleaning pulse.
If it is cleaned continuously or at intervals that are too short, the protective residual cake will be completely destroyed. The consequences are:
Emissions peaks: With every shot, the medium is bared, and fine dust penetrates the clean gas side unimpeded.
Blindness of the medium: As no cake layer protects the pores, fine individual particles are drawn deep into the fibre structure by the suction flow and become irreversibly wedged there. The filter becomes clogged from the inside.
A simple timer control rigidly cleans based on seconds (e.g., a valve every 20 seconds), regardless of whether the filter is clogged or clean. This leads to increased compressed air consumption, dry cleaning (destruction of the cake), and blockage during shock loads in cases of low dust load. The delta p control is intelligent: it only starts when the filter is loaded (e.g., at 1,400 Pa) and stops (with optimal setting) as soon as the protective residual cake is reached (e.g., at 900 Pa). This saves expensive compressed air, protects the material, and increases filter performance.
The most common misconception is: „If the filter is blocked, the valve must remain open for longer to clean it with more air.“ The opposite is true. The cleaning effect depends solely on the shock-like pressure wave (rate of pressure rise) in the first few milliseconds. The optimum pulse duration is an extremely short 0.1 to 0.15 seconds for filter bags and hoses (the bag is suddenly inflated and shakes off the dust), and 0.3 to 0.35 seconds for filter plates, cartridges and sintered elements (initial pulse with a short follow-up flush).
If the valve remains open for too long, only unused compressed air will flow through afterwards. This wastes energy, overloads the compressed air tank, and mechanically blows dust particles through the medium.
If the pressure gauge on the compressed air receiver drops by more than 1.0 to 1.5 bar during an impulse, then either the tank volume is too small or the supply line from the compressor is undersized. The subsequent valves then clean with too little pressure. The filter cake is no longer cleanly ejected, and the differential pressure of the entire system rises massively.
Sintered elements (such as Sinbran) are rigid sintered lamellar bodies with an extremely dense PTFE coating. Unlike needle-punched felt, they operate entirely on the principle of surface filtration.
No breakthrough possible: Because the PTFE surface forms an absolute mechanical barrier, particles cannot be pressed through the material even at extremely high pressures (e.g., 2,500 Pa).
Calculated load: These elements are more expensive to purchase. To operate them economically, they are deliberately run with a very high filter surface loading ($v_s$) – meaning a lot of air is forced through a small area. This artificially created, higher flow resistance is completely normal, factored into the system design, and unlike fabric filters, does not lead to the destruction of the medium.
A retrofit with pleated elements (cartridges/panels) is a potential problem solver when:
The system needs to handle more air volume (m³/h) through production expansion, but the housing cannot.
This is a single-filter system in continuous operation that suffers from extreme \(\Delta p\).
For damp, hygroscopic or sticky dusts (e.g., fine sugar, salt, damp.
In depth filtration, particles penetrate the filter medium and are deposited within it. The entire filter volume acts as a reservoir for the separated substances. This type offers a very high separation efficiency, but it cannot be fully regenerated because the particles become firmly embedded in the material. It is typically used, for example, in intake air or final filtration.
Mixed filtration begins with partial impaction of particles into the medium. After this, a so-called filter cake forms on the surface, which carries out the actual separation. The pressure loss increases during operation, but can be reduced again by cleaning, for example with pulse-jet. This type of filtration is often used for aspiration, dust removal and product transport.
In surface filtration, particles remain directly.
For the safety-related design (housing construction, relief areas or suppression systems), the following four dust parameters must be considered in advance:
K_St-value [bar·m/s]: The specific characteristic value for the severity of a dust explosion. It describes the maximum pressure rise rate in a defined vessel.
P_max [bar]: The maximum explosion overpressure generated in a closed space at optimal dust concentration.
Minimum ignition energy (MIE) [mJ]: The smallest electrical or thermal energy (e.g. from a spark) sufficient to ignite the dust-air mixture.
MIT (Minimum Ignition Temperature) [°C]: The lowest temperature of a hot surface at which a dust cloud ignites.
Dusts are divided into three explosion classes based on their K_St value, which defines the hazard potential:
St 1 K_St > 0 to 200 bar·m/s: Weak to moderate explosion (e.g. coal dust, wood dust, flour).
St 2 K_St > 200 to 300 bar·m/s: Strong explosion (e.g. cellulose, some plastics and pharmaceutical dusts).
St 3 K_St > 300 bar·m/s: Extremely strong explosion (metal dusts such as aluminium, magnesium or titanium).
Passive systems (like rupture discs, panels, or flameless venting systems) simply vent the overpressure and flames of an explosion to the outside. For St 3 metal dusts, this is generally no longer permissible or physically possible for two reasons:
Extreme Druckanstiegsgeschwindigkeit: Bei St 3 explodiert das Gemisch so rasant, dass passive Klappen mechanisch zu träge reagieren. Der Druck im Filter steigt schneller an, als die Berstscheibe oder Klappe die Masse der Luft entlasten kann. Das Gehäuse reißt.
Unlöschbare Metallbrände und Sekundärexplosionen: Metallstäube entwickeln extrem hohe Explosionstemperaturen (oft über 2.000 °C). Die austretende Flammen- und Glutwolke ist riesig und reagiert heftig mit der Umgebungsluft. Zudem lässt sich ein solcher Metallbrand nicht mit Standardmitteln löschen. Das Risiko für die Umgebung ist bei passiver Entlastung unkontrollierbar hoch
Tritt im Filter eine Explosion auf, schlägt die Flammen- und Druckwelle mit enormer Geschwindigkeit durch die Rohrleitungen zurück in die Produktionshalle (Flammendurchschlag). Die Rohgasseite muss zwingend entkoppelt werden, um nachgeschaltete Maschinen und Mitarbeiter zu schützen. Dies geschieht über:
Explosionsschutzklappen (Rückschlagklappen): Im Normalbetrieb hält der Saugstrom die Klappe offen. Kommt es zur Explosion, drückt die Druckwelle die Klappe schlagartig zu und verriegelt sie mechanisch.
Schnellschlussschieber / Schnellschlussventile: Diese werden über optische Sensoren (Funken-/Flammendetektoren) oder Drucksensoren im Filter elektronisch angesteuert und schließen die Rohrleitung mittels Gasdruck oder Federkraft in Millisekunden gas- und flammendicht.
Zellenradschleusen (flammendurchschlagsicher): Beim Staubaustrag am Trichter verhindern speziell ausgelegte Schleusen mit geringen Spaltmaßen und einer Mindestanzahl an Rotorblättern, dass eine Explosion nach unten durchschlägt.
Auch auf der Reingasseite (hinter den Filterelementen) besteht das Risiko, dass bei einem unbemerkt defekten Filtermedium (Schlauchbruch) zündfähiger Staub auf die Sauberluftseite gelangt und sich am Gebläserad entzündet. Folgende Schutzkonzepte sind üblich:
Raus ins Freie (sicherer Bereich): Die Reingasluft wird direkt über Dach ins Freie geleitet. Im Explosionsfall verpufft die Energie in der Atmosphäre.
Reingasseitige Entkopplung: Ist das Reingasleitungssystem sehr lang oder führt durch sensible Gebäudeteile, werden auch hier Schnellschlussschieber oder Entlastungsventile verbaut, um den Flammenweg zu blockieren.
Passive Systeme (Reaktiv ohne Eigenstrom): Sie benötigen keine Elektronik oder Sensoren. Sie reagieren rein mechanisch auf die physikalischen Kräfte der Explosion (z. B. Berstscheiben, die bei einem bestimmten Überdruck reißen, oder Explosionsschutzklappen, die durch die Druckwelle zugeworfen werden). Sie sind günstig, erfordern aber oft große Sicherheitszonen im Außenbereich, da Flammen ungehindert austreten.
Aktive Systeme (Präventiv mit Sensorik & Aktorik): Diese Systeme erkennen die Explosion bereits in ihrer Entstehungsphase (im Millisekundenbereich). Drucksensoren oder Infrarot-Flammendetektoren melden den beginnenden Druckanstieg an eine Zentrale. Diese löst blitzschnell Gegenmaßnahmen aus (z. B. Explosionsunterdrückungssysteme, die Löschpulver in den Filter jagen, bevor der Druck zerstörerische Ausmaße erreicht, oder pyrotechnisch schließende Schnellschlussschieber). Aktive Systeme sind bei St 3-Stäuben oder bei Innenaufstellung von Filtern oft die einzig zulässige Lösung.
