Cleaning with air
October 1st 2004

Amajority of industry sectors have need for use of vacuum equipment of some sort. While for a majority of these the primary application is cleaning or fume extraction, for a significant minority the requirement is biased towards materials recovery for recycling or re-use. In neither case is the choice of equipment straightforward as both the type of material being handled and the working environment have to be considered.

Although most particulate materials are apparently benign the risk of generation of static electricity and the explosive properties of fine materials like sawdust and flour have to be considered. Equally, when dealing with highly abrasive materials such as casting sand their effect on the components of the system becomes an important issue. There are also some working environments such as refineries, offshore installations and on ships where equipment capable of generating sparks constitutes a flammability hazard.

For some years the Norwegian company Norclean, which was recently acquired by the Nederman group, has specialised in solutions for this type of niche market application. A key product line within its portfolio is the range of pneumatic ejector powered vacuum units, that offer intrinsically safe operation.

These are complemented by electric powered fan based systems. Both fixed/skid mounted and wheeled portable units are available and all can be customised to meet specific requirements.

Whereas an electric vacuum unit contains an electric motor and fan unit, a pneumatic ejector has no moving parts. Instead passing compressed air through a venturi-type ejector generates the vacuum. In simple terms the venturi is a constriction in a tube with a smooth aerodynamic entry and exit geometry. As air travels through the narrow section its speed increases and its pressure reduces. By tapping into the narrow section this pressure drop can be harnessed to generate a strong vacuum (up to 6800mm water column.)

The technology lends itself to applications in areas where electrically powered systems would be regarded as high risk. Additionally, with no moving parts it is very robust and therefore well suited to installations where corrosive or abrasive materials need to be handled on a regular basis. This can entail use of stainless steel or anti-abrasion materials for internal and external surfaces, while provision for earthing can be made to prevent the risk of static electricity buildup.

As controls and legislation affecting workplace safety become more widely implemented, what was a niche application is beginning to become more mainstream.

However, in many cases what at first looks like an additional safety related overhead can often prove capable of paying its way, especially where an element of materials recovery is involved.

Partly as a result of this, the basic reliability and flexibility of ejector powered high vacuum units has proved attractive to a wide range of industries from foundries and shipyards to chemical and food manufacture.

Motor industry examples include initial cleaning of machined components. Whereas it was once the norm to use air blast to remove coolant and loose metal chippings following machining, workplace environmental and safety considerations have made it less acceptable. In response to this some manufacturers have installed ejector powered vacuum systems to perform the ‘cleaning’ function without random soiling of the immediate working environment or the operator; in practice the vacuum systems have also normally proved more effective in the primary task.

Further advantages have accrued from the use of ejector type of extraction technology in foundries. The quartz sand, clay and coal used, together with fly-ash, cause heavy dust emissions that can cause wear or breakdown of sensitive production machinery and electronic control systems. Furthermore, environmental protection and workplace safety considerations demand that the workplace be kept as clean as practicable. In a situation like this an ejector-type extraction system can be configured as a reliable solution for local use. It is unaffected by the environment in which it operates and acts as a preventative maintenance measure for other equipment.

Along with shotblasting, chemical and food industry applications tend to focus on material recovery and cleaning in equal measure. Incorporating a preseparator allows expensive materials to be recovered that would otherwise be wasted, while use of an ejector system with anti-static measures removes any risk of dust explosion. This dual capability allows the cost of the installation to be offset against the value of the material that is recovered. Where there is no explosion hazard a similar system can be configured using an electric powered vacuum unit.

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