Vacuum pumps:  Technology and applications

When considering vacuum technology, a good starting point is with oil lubricated, rotary vane vacuum pumps. This technology operates via an eccentrically installed rotor which rotates inside a cylinder and centrifugal forces throw the moveable vanes towards the cylinder wall, separating the space into chambers. When the chambers are connected with the pump inlet, gas is sucked in, compressed during the rotation and then forced into the oil separator.

Differential pressure constantly causes the oil to be pulled into the pump cylinder and the oil and the process medium are discharged into the separator box. The oil and exhaust air are separated by filters and gravity. The oil is collected, filtered and drawn into the compression chamber and re-used.

Used extensively in food processing and packaging, these vacuum pumps are also used in plastics, woodworking, pneumatic conveying, metallurgy, chemicals and pharmaceuticals. The benefits include increased energy efficiency with reduced power requirements and optimised pumping speeds at low end pressures, enabling faster pump-down times and shorter process cycles.

Rotary vane vacuum pumps are reliable and suitable for continuous operation, while pumping large volumes of air when working at ultimate pressure. Maintenance is normally limited to oil changes and the periodic replacement of filters.

Another widely used method is dry running, rotary claw vacuum pumps, featuring shaft mounted asymmetric rotors or ‘claws’ which rotate in opposite directions within a chamber, synchronised by gears. The claw design causes air to be sucked into the chamber as it rotates, compressed within the housing and then discharged under pressure.

A key advantage is the oil-free, non-contact design of the rotors, resulting in virtually no wear, therefore requiring minimal maintenance. Energy efficiency enables cost savings of up to 60% in some cases. Variable speed control can also be used to match pumping speed, end pressure and flow to meet process demand.  

Another dry running technique is the screw vacuum pump. Two variable pitch screws rotate inside a cylindrical chamber, drawing gas into the pump and compressing it within the length of the screw and then the gas discharges into the pump silencer. As with rotary claw pumps, there is no contact between the screw rotors and they require no lubrication. Cooling is achieved via an external water supply running through the pump’s cooling jacket.  

Screw vacuum pump technology is used in many tough industrial environments including furnaces, heat treatment, metallurgy, coatings, drying and impregnation, chemicals and pharmaceuticals, plastic extrusion, rubber, absorption and degassing, remediation and the semiconductor/electronics sector.

Centralised vacuum systems

Pumps tend to increase noise levels and generate unwanted heat in production areas and require additional air conditioning to maintain safe working temperatures.  If production capacity increases, more pumps are needed adding further heat and noise, and environmental legislation requires the eradication of oil mist contamination. A solution to all these issues is a centralised vacuum system, thereby relocating the pumps to a separate plant room where the vacuum is supplied via pipework and control systems.

Centralised vacuum systems offer reduced energy costs due to lower installed power, as the system looks at overall vacuum requirements, often reducing installed power by 20 to 30% dependant on the process and necessary vacuum. Systems reduce heat emissions and the pumps are controlled by process demand, running when needed and reducing energy use. Fewer parts and repairs are required while maintenance is reduced with lower lubricant consumption and less waste oil disposal.

Selecting the right product at the outset is critical and involving equipment manufacturers at the planning stage will pay dividends. There are many kinds of vacuum technologies and solutions available, so calling on their knowledge and experience will ensure the best result.