In the past industrial vacuum pumps were synonymous with high oil carryover, excessive noise and prohibitive energy costs. In parallel with developments in other air movement technologies, vacuum pumps have recently undergone substantial advances in terms of reliability, performance, quiet operation, and energy economy. To assist end users in selecting the best type of equipment for their application, here is a brief overview of the operating principles and current developments in the four main categories of industrial vacuum pump.
Operating on the simple principle of centrifugal force acting on an eccentrically mounted rotor with radially movable blades, this tried and tested technology has been subject to a host of design innovations to improve performance and reduce total operational costs. Compared with earlier generations, power demand at the same volume flow is now about 15 per cent lower. In general, the latest units are more compact, with vibration levels that are 3 to 5 dB(A) quieter than their predecessors. They can also now operate at lower temperatures, which protects oil consistency and extends service life as well as maintenance intervals.
The reliability of these ubiquitous machines is attributable to their basic, sturdy construction and good oil retention at all operating pressures. In the latest designs, the pumps incorporate internal injection channels. This reduces the number of gaskets and the amount of external piping required. In some cases, the number of components has been reduced by as much as 20 per cent, further minimising the risk of leaks and subsequent failures.
Capable of an ultimate pressure between 0.1 and 0.5 mbar, rotary vane vacuum pumps are suitable for packaging, woodworking, plastics, paper and printing, material handling and other demanding applications.
Liquid ring vacuum is regarded as the optimum technology for handling extreme vapour loads and pumping wet or dry gasses with a high tolerance for liquid carryover, especially on condensable processes such as distillation, drying and evaporator duties. Single stage pumps have very good efficiency above 200 mbar and are ideal for general process applications such as filtration and dewatering, pump down or evacuation duties.
Liquid ring pumps are equipped with a fixed blade impeller, located eccentrically within a cylindrical casing. As the impeller rotates, liquid (usually water) is thrown out by centrifugal force to form a liquid ring around the circumference of the casing. This seals the tips of the impeller and creates separate enclosed gas chambers between each blade. In general, capacities range from 170 to 37,500 m³/h.
Dry claw vacuum pumps offer the advantage that there is no lubrication in the main pumping chamber, which eliminates the possibility of any contamination of the application process.
These types of vacuum pump employ two claw-shaped rotors running in opposite directions that don’t touch each other or the pump chamber. This makes them virtually free from wear. They are also among the quietest vacuum technologies; which contributes to an agreeable working atmosphere in a wide variety of dry pumping applications ranging from packaging lines, pneumatic conveyors, and clamping systems for CNC machines, to moulding machines, drying processes, and central vacuum supply systems.
In two-stage versions, two synchronised pump chambers work in series to achieve high performance at operating pressures below 200 mbar and improved efficiency on continuous process duties such as drying, degassing exhausting and solvent recovery.
Multiple units are also available, which combine between two and four dry claw vacuum pumps, depending on the application, in a single compact housing. In this configuration one of the pumps in each multiple unit features variable speed drive, allowing the vacuum to be adapted precisely to the application requirements. This results in improved efficiency and economy by reducing the power required and therefore reducing cost of ownership.
Volume flows for dry claw vacuum pumps vary between 65 and 1230 m3/h and units typically have an ultimate vacuum of 140 mbar(a). Some of the latest pumps on the market can reach 50 mbar(a).
Rotary Screw pumps are based on proven compressor screw technology and provide significantly higher performance levels and reduced maintenance, noise and heat emissions compared to conventional oil-sealed and dry vane vacuum pumps. With the application of variable speed drive, it’s possible to tailor vacuum production to precisely meet process demand. When installed as part of a central vacuum system, energy consumption can be reduced by up to 50 per cent. With a maximum flow rate in the region of 5004 m3/h, they are particularly suited for large industrial vacuum users in the glass, plastics, canning and food packaging industries.
This technology has been designed for specific industries and is optimised to perform at 400 mbar and below. At operating pressures above that, and in certain applications, other types of vacuum pump technology may be more suitable. For instance, a dry claw pump on a conveying line in a harsh operating environment, or a liquid ring pump where excess water is present, or an oil-injected vane pump in smaller point-of-use applications.
Rotary screw vacuum pumps are usually equipped with electronic process controllers and variable speed drive, which makes them extremely economical to run. Additionally, a pressure set point control function ensures the pumps deliver the lowest possible vacuum flow with which the required vacuum can be maintained. As a result, no excess energy is wasted and life cycle operating expenses are significantly reduced.
Finally, it’s also worth considering the merits of remote monitoring when specifying an industrial vacuum pump. Recent advances in connectivity technology mean that central vacuum systems and individual machines can now transmit live performance data to a company’s engineering team via their smartphone, PC or tablet. This makes it possible for plant and service engineers to receive all the information required to take a proactive approach to the maintenance of their industrial vacuum pumps: from machine alarms and faults to visualised representations of demand and load for complete site installations.
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