The performance of the vacuum is actually determined by the air flow rate (lt/s) and the vacuum (mbar/kPa) and not by the power rating of the vacuum motor, which is very often wrongly being used for comparing performances. New motor designs are more powerful, need less energy and are cheaper to run. There are dry, wet and wet/dry vacuums with different filter systems, different tanks seizes, one to three suction motors or heavy duty motors for continuous operation for different applications.
Dry vacs for industrial applications
Dusts, thought to be harmless, can also be health endangering in very high concentrations per cubic metre air. Some dusts can have a highly toxic effect even at low concentrations and cause irritation of the skin, bronchial tubes and mucous membranes or illnesses such as asthma and cancer. Such dusts are formed in industrial production processes (including heavy metal dusts) and trades (asbestos, wood or plastics). Added to this is that some dusts, in high concentrations, irrespective of whether they are health endangering or not, can be highly combustible or potentially explosive.
The particle size is also significant for the hazardousness of dust. In contrast to coarse dust (particles with a diameter of > 10 µm), fine dust (particles with a diameter of < 0.1 to ≤ 10 µm) can enter the lungs via the respiratory passages. If such fine and ultra-fine dusts also happen to contain heavy metal such as lead, beryllium or mercury or substances such as sulphur, nitrogen compounds or hydrocarbons, they become even more harmful.
Until a few years ago, the so-called MAC value (maximum allowable concentration) was used as a standard for assessment of the hazards of dust concentrations at workplaces. With the introduction of the new international accepted Ordinance on Hazardous Substances, a new assessment concept known as the Threshold Limit Value (TLV) applies. In practice, this means the lower the TLV for dust, the higher the health risk.
The filter efficiency in particular is taken as a basis for machine classification. Based on DIN EN 60335-2-69 Appendix AA and E DIN IEC 61 J/94/CD, modern vacuum cleaners (vacs) are divided into the dust classes “L”, “M” and “H”.
L-class dust (slightly dangerous) vacs are suitable for dust with a TLV of > 1 mg/m³. This includes substances such as gypsum, mica, lime, kaolin, molybdenum or tantalum. Since the filter efficiency (separation efficiency) requirements of vacs can easily be maintained, the maximum dust permeability of the filters can be maximum one per cent. L-class dusts are therefore not subject to any disposal regulations.
L-class dust vacs are preferably used in trades for removing dirt. However, higher M-class vacs are also recommended for this purpose.
The filter separation efficiency of M-class dust (moderately dangerous) vacs refer to dusts with a TLV of > 0.1 mg/m³; the maximum permeability is < 0.1 per cent. M-class dusts also consist of copper, platinum, nickel, borax and wood. These vacuum cleaners are therefore used mainly in building and woodworking as well as in the automotive, restoration, chemical and pharmaceutical industry. Since the disposal or removal of dusts from the machine must take place with low dust turbulence, M-class dust vacs are provided with a paper filter bag with slide closure and dust disposal bag. These vacuum cleaners also have a flat pleated filter for cleaning the machine exhaust air or alternatively a polyester fleece flat pleated filter for wet applications and abrasive material.
All dusts with a TLV of < 0.1 mg/m³ fall into the H-dust class category (highly dangerous). The filter efficiency requirements of vacuum cleaners are very high with a maximum permeability of < 0.005%. The group of H-class dusts includes health endangering and pathogenic substances such as beryllium, lead, cadmium, cobalt, asbestos as well as dusts contaminated with bacteria, mould and viruses. H-class dust (also M class) vacs are called safety vacuum cleaners. They are used primarily by roofers, in building and installation as well as the electrical, pharmaceutical, chemical, metal and plastics industry.
The dust produced in these areas must be removed completely. For this reason, H-class dust vacs are provided with so-called H-class safety filter bag, which efficiently retains this class of dust. For dust-free replacement, this bag has a plastic cover, which is slipped over the bag and subsequently closed. The H-filter is usually flat pleated and cleans the exhaust air. The filter medium consists of glass fibre mats with a fibre diameter of about 1 to 10µm. For safe replacement, the H-filter has a frame for disposal together with the plastic bag in compliance with the statutory regulations. The classifications apply throughout Europe.
In the past, asbestos was regarded as a universal building material with many positive attributes such as good thermal insulation, excellent fire protection properties and a very good coefficient of friction, particularly brakes for motor vehicles. Today, asbestos dust is known to be extremely dangerous and can cause lung cancer. Only H-class cleaners approved for asbestos should be used for this purpose.
However, not only health endangering dusts pose a potential hazard to humans and the environment, explosive dusts must also be safely removed. This initially requires a precise knowledge of the types of fine dust powder, flour, wood or metal. A detailed knowledge of the combustion and explosion behaviour of these dusts allows meaningful and effective protective measures to be taken. These include the vacuuming of combustible dusts (except for dusts with an extremely low minimum ignition energy ME < 1mJ). Only vacuum cleaners complying with the ATEX Directive (94/9 EC 2003) may be used for this purpose. This directive regulates, among other things, the suitability of the machines for use in potentially explosive atmospheres. It distinguishes between explosive gas and combustible dust atmospheres and classifies the equipment intended for use in these areas.
Cleaning Filter systems
The most advanced solutions offer an automatic filter cleaning during vacuuming, i.e. the Karcher Tact² System which cleans continuously parts of the filter by air blasts, so no vacuum work has to be interrupted because of blocked filters or for cleaning the filter.
Even if vacuum cleaners are protected for use in combustible dust atmospheres, they cannot be used everywhere due to the varying requirements applicable to their use in potentially explosive atmospheres depending on the hazard potential. The ATEX directive therefore defines different unit groups and hazard categories.
Units of group 1 are intended for use in underground mines (M1 and M2: M = Mining). However, units of group 2 are approved for use in non-mining areas. Both unit groups are subdivided into three hazard categories “very high” (1), “high” (2), “normal” (3).
ATEX requirements for suction devices are defined analogous to these groups and hazard categories.
Machines in hazard categories 1 and 2 (combustible dust atmospheres Zones 20 and 21) are usually permanently installed suction devices.
Mobile vacuum cleaners, however, fall into the hazard category 3. These machines can be used in combustible dust atmospheres Zone 22. Explosive dust atmospheres only occur here rarely and briefly (including mills, warehouses, pharmaceutical, chemical, food, electrical, paper and powder processing industry). Since explosive dusts in Zone 22 can have a toxic effect, the filter efficiency requirements of vacuum cleaners are the same as for dust classes “M” or “H”.
Machines approved for Zone 22 are recognisable by the classification “B1” according to DIN EN 60335-2-69 Appendix AA . These machines therefore have the minimum classification “B1 M” or “B1H” and the degree of protection IP 54 (DIN 40050). In order to neutralise dangerous and explosive dusts, hazardous material is drawn through a water bath in the case of some vacuum cleaners. By contrast, water-reactive substances must be vacuumed dry and filtered. Today, there are vacuum cleaners that can do both.
Wet vacuums for industrial applications
Wet pick is less complicated as normally no filters are required. The dirt is captured by the liquid and just requires a water shut-off the tank lid full not to damage the vacuum motor. For bigger tank vacs a drainage or pump-out solution is required due to the weight. For certain applications a mesh filter in the tank is required to separate particles from the liquid so separate reuse or recycling can be done.
The required right filter system, optimal tank size, desired performance, selection of accessories and the right tools are needed for providing the best cleaning solution. Depending on more stationary use or a lot of transportation, required bigger and sturdier wheels should be chosen with ergonomic handles and storage place for tools and hoses. The clients should ask the supplier for different options and not relay on standard tools which might not give the optimum cleaning solution.
Ruediger Schroeder Managing Director-Karcher Cleaning Systems Pvt Ltd