Cause to filter

In general terms, air filtration requirements break down into four basic categories: • Particle filters remove dust, powder, smoke, spores, bacteria and other particles; • Activated carbon filters remove chemical vapours, pollutant, odorous and toxic gases; • Combination filters control both particle and gaseous contaminants in one unit; and • Special filters/housings are used for specific or unusual applications where standard types are unsuitable. Within each category there are many different filter types. At the lower end of the efficiency range particle filters can be supplied as disposable or cleanable panels. Disposable bag filters are also widely used for the removal of airborne particles where high dust loading capacities are required. For High Efficiency Particle Arrestance, HEPA filters are employed to achieve efficiencies of up to 99.997%. Due to their critical nature all filters should be individually tested and certified by the manufacturer as well as in situ if so desired. HEPA filters can be manufactured in either cylindrical or panel format. The panel filters, with compact pleats in depths of up to 95mm, have caseworks that are normally fabricated in galvanised steel, aluminium, stainless steel or PVC, but other materials such as MDF ( for incineration disposal ) are often specified.

Double protection Cylindrical filters are normally produced by moulding close pleated packs into rigid polyurethane circular end caps or by encapsulating the pleated packs within preformed spinnings. The pleated paper should be protected on both inner and outer faces with mesh screens to prevent damage during handling and installation. Sealing gaskets such as a leaf seal system can be moulded into the end caps to provide excellent sealing properties. Where there is a danger of operator exposure to hazardous contaminants during filter changeover, safe change filter systems must be specified. These ensure that as exhausted/contaminated filters are removed from the housing, any hazardous, toxic or radioactive contaminants will be sealed inside a safe change bag. Activated carbon filtration has for many years been recognised as a successful method of controlling/removing dangerous and noxious gaseous contaminants from airstreams where critical performance is necessary. At the heart of any carbon filtration system are the activated carbon cells contained within the filter unit. EMCEL carbon filter cells are manufactured to a patented design incorporating a honeycomb matrix that creates a strong, rigid and robust holding structure for the granular carbon. This technique prevents the problems of carbon granular settlement, pin-holing and carbon dust liberation that can be associated with loose-fill tray designs, as well as the sagging or bowing that can occur with bonded slab type carbon trays. For many applications standard grade carbon combines the high activity necessary to effectively adsorb a broad spectrum of odours, gases and chemical vapours, with the granular hardness to minimise attrition under the action of airflow. For enhanced removal of specific contaminants, such as acid gases, ammonia, arsine, formaldehyde, hydrogen sulphide, mercury vapour, nitrogen dioxide, phosphine, radioactive isotopes and sulphur dioxide, specially impregnated carbon grades are utilised. Carbon filters units are available in a vast range of casework designs/formats, with replaceable carbon cells or as completely disposable units. Safe change systems for carbon filters are also a requirement where exposure to dangerous contaminants must be prevented when filter cells are replaced. Combination filter units can be made in various configurations to provide two- or three-stage filtration formats. A typical three-stage unit would include particle pre-filter, a HEPA section and then activated carbon cells. This would provide the removal of dust/particles plus odours, vapours and gases within one unit – an advantage for applications with size or space restrictions and where disposal costs are an issue. Existing particle-only systems can also be converted to combination filtration, possibly without an increase in unit size. Safe change systems are also available for combination units. Disposable combination panel filters can be used to give good odour control performance and particle filtration in a lightweight format. A typical configuration for three-stage filtration is polyurethane foam particle filter bonded to high efficiency pleated media (F6-F9), then a carbon impregnated synthetic media, all encased/ bonded within a rigid card frame. Wherever possible standard sizes and shapes of filters should be chosen but some applications require special filters or housings. Recently, 13 purpose-built, in-line HEPA safe change units were manufactured for a leading pharmaceutical company. To comply with stringent on-site requirements 316L stainless steel was essential for the housings, mounting stands and HEPA element casings. Designed and produced to meet customer airflow, flange diameters and size parameters, the finished units were polished, engraved, individually tested and certificated prior to despatch.