Cruma Filters for Filtration of Gases, Solids and Aerosols in their Ductless Fume Hoods

All the activated carbon filters of Cruma fume hoods have been impregnated, manufactured and tested according to the requirements of the CEN-141 standard.

 

Type A: adsorption of vapours and organic solvents (ketones, ethers, alcohols, cyclics,...). Activated carbon without impregnation.

Type BE: Inorganic gases like Cl2, HCl, HNO3,... and volatile sulphur compounds (H2S, H2SO4, SO2, SO3,...). Activated carbon with impregnations of metallic compounds and neutralising salts.

Type K: specific for NH3 vapours and amines. Activated carbon impregnated with metallic complexes.

Type F: specific for formaldehyde and derivatives. Impregnated with Cu.

Type ABEX: mixed type among filter A, BE and K. It is able to retain molecules belonging to all 3 groups. It is impregnated with inorganic neutralising salts, metallic salts, complexes and Cu.

 

Specific types: there are special filters available for Hg (type MD) and radioactive iodine (type GD).

 

The designation D indicates that a HEPA absolute filter class H14 (UNE-EN-1822 standard) is fitted as a pre-filter before the activated carbon filter and is required for applications that generate particles and / or aerosols.

 

 

G-type hoods are those with a single activated carbon filter (impregnated or not) for filtering fumes.

GS-type hoods are equipped with a double HEPA carbon filter for filtering fumes and particles (solids and aerosols).

 

 

HEPA filters are the most important component in the Cruma laminar flow cabinets (CLFC), which have a wide range of applications in fields such as microelectronics, scientific and health research, etc. They are also known as ‘absolute filters’ and were developed during World War II to remove radioactive particles from the air in the nuclear industry. Since then they have undergone continual advances to satisfy the ever increasing demand for smaller particles.

A conventional HEPA filter consists of a special continuous v-shaped fibreglass sheet with corrugated aluminium separators between the pleats. This piece is the actual filtering component, which is fitted into a rigid frame using a special polyurethane composite. The more advanced ‘minipleat’ filters are the ones included in the Cruma LFC assembly. A very tight pleat in the filtering element characterises them. Several techniques may be used to reduce the space between the pleats. Thermoplastic spacers are also used as pleat separators.

The technique of arranging them in pleats gives the filters their filtration efficiency. The HEPA filters used by Cruma are Class H-14, according to the EN-1822 standard, providing a minimum efficiency of 99.995% for 0.3 micron particles, according to test DOP. The highest HEPA category is H-14. High quality filters such as those inserted in Cruma cabinets are tested for their efficiency on submicron particles, as well as to determine the pressure drop (airflow resistance) they cause.