Multi Pocket Filters

Bag filters are the most common type of filters used in HVAC systems for industrial and commercial applications to improve air quality and comfort. The filters in the supply air are used as first and second filter stages, either as complete filtration solutions for these applications or as prefilters for cleanroom process applications. The filter bags are also used in the exhaust air or in recirculation systems to protect the air handling units. Bag filters have a significantly higher dust holding capacity and longer lifetimes than other filters.

The multi-pocket design uses synthetic media to achieve maximum efficiency, with minimal resistance penalties and high dust loading capacities.

Types filter bags

There are four different finishes available for multi pocket filter bags:

• Standard polyester; 
• Antistatic; 
• Universal Chemical Finish;
• Nomex. 

Standard Glazed multi pocket bag filters are made from a polyester needlefelt. They are used for general dust collection.

Antistatic finish pocket filters are suitable for applications where static electrical charges can build up from certain combustible dusts such as ground plastics, sugar and flour. To control the risk of explosion from electrostatic discharge, anti-static bags that are effective conductors of electricity are available. These bags are very effective at dissipating electrical charges from the powder and dramatically reducing the risk of explosion. Very small amounts of dust in large volumes of air have a high risk of explosion. Ignition sources need to be carefully controlled. A charge of static electricity can build up as particles move in the airflow, producing a potential ignition source. DSEAR (The Dangerous Substances and Explosive Atmospheres Regulations 2002) requires all workplaces where substances that could give rise to fire or explosion are handled or stored must be fully assessed and protected. ATEX directives concern the supply of equipment and components where they are for use in potentially explosive atmospheres.

Universal Chemical Finish resists Moisture & Oil. Liquid Repellent finishes are recommended for the filter media when the filter bags need to be either hydrophobic (repels water) or oleophobic (repels oil). There are several reasons for using a liquid repellent finish. As air cools in the filter unit, the gas can pass through the dew point and water or other vapours can condense onto the filter media. This will help the dust particles cling to the filter media and make the cleaning mechanism less effective. If the dust is hydroscopic or the particles react chemically with water, then the dust particles that collect on the damp surface of the filter bags can form an impermeable layer that is firmly attached to the filter media. In some circumstances dust particles can even carry oil. This would lead to untreated bags becoming saturated with oil and consequently a much reduced effectiveness and a significant fire hazard.

Nomex filter bags are flame retardant and are often used in higher temperature dust filtration applications such as Asphalt mixing plants, cement kiln smoke filtration in cement plants and smoke filtration on steel melting furnaces. The Nomex coating allows for continuous use in temperatures up to 200° celcius in dry conditions.

Ducting Express stock multi pocket bag filters to fit the whole range of DCE Donaldson filter units. Each size is available in three different finishes mentioned above depending on your process needs. Filter bags are available in the following sizes:

• UMA 40 - 9 pockets
• UMA 70 - 12 pockets
• UMA 100 - 18 pockets
• UMA 150 - 18 pockets
• UMA 250 - 29 pockets
• UMA 350 - 28 pockets (2 x 14 pocket bags)
• UMA 450 - 36 pockets (2 x 18 pocket bags)
• UMA 750 - 48 pockets (2 x 24 pocket bags)

Multi pocket filter bags are also available for use with the following dust extraction filter units:

• Airmaster
• DCE
• Dustraction
• DustX / DEI / Dust Extraction International
• Filtex
• Heaton Green
• Mardon MS50 & MS100

How to Install Pocket Filters

It is important that the bags are installed with the pockets running vertically from top to bottom. This allows the pockets to fully inflate and operate efficiently. Failure to install in this way will result in higher pressure loss, uneven filtering through the pocket length, increased energy usage and a much reduced filter life span.

If you are not sure what pocket filters you need, or require further information about any of our multi pocket bag filters give us a call on 01455 616 444. A member of our knowledgeable team will be able to help answer any questions that you may have.