Technical questions on selection and sizing

How do we identify a filter element whose marking has worn away?

By its dimensions and its mounting, not by its appearance. Record the overall dimensions, the end cap or collar type, the direction of fitting, the visible nature of the medium and its weave, and whether a gasket or a reinforcing mesh is present. Photograph the whole part, then its end close up. Note the machine or housing it came out of, and what it filters: at equal dimensions, two elements can differ by the medium alone. With that, identification succeeds in the great majority of cases.

Further readingGlossary of industrial filtration

What decides the filter area of a dust collector?

The airflow to be handled, the filtration velocity you allow yourself, and the cleaning method. The ratio of flow to area gives the face velocity, and that is what sets the pressure drop reached and the service life. The admissible velocity is not a constant: it depends on the nature of the dust — fine, abrasive, sticky, hygroscopic — on the medium chosen and on the cleaning energy available. A value carried over from another installation is the commonest source of error.

Further readingGuide to choosing a filter medium

A nominal and an absolute rating — what is the practical difference?

A nominal rating states partial retention at a given particle size, and its definition varies between manufacturers. An absolute rating states near total retention beyond that size, established by a standardised test counting particles upstream and downstream. In practice: two elements at the same nominal rating can behave very differently, whereas two at the same absolute rating are comparable. As soon as fluid cleanliness is a process requirement, reason from the absolute one.

Further readingGlossary of industrial filtration

At what pressure drop should an element be replaced?

At the final value given by the builder of the installation and by the medium, and at no other. There is no universal threshold: the same pressure drop is normal on a fine stage and abnormal on a pre-filter. What does read across, though, is the shape of the rise. A slow, steady rise is the expected cycle. A sudden rise points to failing cleaning or an abnormal load; a drop that stays low while air leaves dirty points to a leak around the element, not to a clean one.

Further readingGlossary of industrial filtration

Can I fit an element from a brand other than the original one?

Often yes, on two conditions checked separately. Dimensional compatibility first: overall dimensions, end type, gasket, direction of fitting, restrainer basket or support mesh. Functional compatibility next: medium, fineness, temperature limit and chemical compatibility at least equivalent to the original. Both together, never just one — an element that fits the housing but whose medium cannot hold the fluid is more dangerous than one that does not fit. The brands we name belong to their respective owners, and we claim no connection with them.

What limits the operating temperature of a filter element?

The medium, but rarely the medium alone. The frame, the adhesives, the gaskets and the end caps each have their own limit, and the lowest of the four governs. A medium that easily withstands the temperature in a cold-glued cartridge fails through its adhesive, not through its material. So read the limit of the complete element, as the manufacturer publishes it, not the limit of the fibre. And beware a frequent confusion: a maximum limit is not the lower bound of a service range.

Further readingGuide to choosing a filter medium

How does moisture change the choice of medium?

In three ways. Through condensation first: a dust that takes up moisture cakes on the upstream face and no longer releases, which calls for a water-repellent surface treatment rather than a different medium. Through chemistry next: some materials hydrolyse in the presence of hot water and lose their mechanical strength without changing appearance. And through the dew point, which has to be stayed above at every point of the installation, drains and cold walls included.

Further readingGuide to choosing a filter medium

What should you send us to get a usable quotation?

Six items, and they are almost always enough. What you filter — the nature of the fluid or dust, with the product safety documentation if you have it. The service conditions: temperature, pressure, flow. The fineness expected, or the result expected if you do not know the fineness. The dimensions of the element in place and its marking, even partial. The type of machine or housing. And lastly the quantity and consumption rate, which decide the packaging as much as the price.

Do you supply elements that appear in no catalogue?

Yes, and it is part of the trade. When no market reference fits — a non-standard dimension, a medium imposed by the process, an unusual end cap, a length that no range offers — the element is made to drawing or to sample. That calls for a witness part or a recorded dimension, and the medium sought. Lead time and minimum quantity depend on the manufacturer chosen: they are part of the answer, not of the question.

Do combustible dusts change anything in the selection?

They change everything, and this is not a question a web page should answer. A combustible dust brings in the zoning of the location, the design of the collector and its explosion relief, the dissipation of electrostatic charge through the medium and its earthing, and the cleaning method. These hold together: dealing with one and not the others does not make the installation safer. A case like this calls for a specific study, with the people who know the installation — write to us and say so from the outset.

Which filter class does my installation need?

The question has no general answer, and being wary of anyone who gives one is a sound reflex. The right class depends on the air quality sought at the outlet, the air quality available at the inlet, the staging already in place, the pressure drop the unit can take and the replacement frequency you can accept. Two neighbouring installations on the same site do not call for the same class. The page on filtration classes explains what each group measures, and that is the right place to start asking.

Further readingAir filtration classes