The niche for venturi vacuum generators
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Venturi vacuum systems have long been the mainstay in pick and place operations, but given the need for energy conservation and efficiency, is there still a role for venturi vacuum generators and suction cups? We get some answers from Steve Sands, product manager of Festo.
Venturi vacuum generators have been around for years. Is there anything better on the market nowadays?
So has the wheel, but it's still a highly effective way of keeping things moving. The same goes for venturi vacuum generators - they are inexpensive to purchase, reliable, easy to fit, and have extremely fast 'time-to-pick' thanks to distributed placement.
Isn't it better to use continuous vacuum generation, or to incorporate some form of energy-saving device?
It really depends upon the application's vacuum cycle. Many venturi vacuum generators are extremely wasteful of energy - selecting the correctly sized component for the application and optimising the peripherals makes an enormous difference to the quantity of compressed air used. For intermittent applications, using venturi modules with built-in control solenoids and vacuum sensors ensures that the air flow is only on when it is actually required.
How else can you minimise compresses air usage in this area?
Understanding the needs of the application in terms of vacuum flow and vacuum level is critical - do you want to evacuate a vessel very quickly to a coarse vacuum level, or is a higher level of vacuum the most critical factor? Having a range of venturi nozzles optimised for the job makes an enormous difference to the air consumption. Also, simple things like ensuring that the tubing that is used has sufficient cross-sectional area are important. Many people try to minimise tubing diameter to reduce the volume to be evacuated - but calculations and tests easily show this approach can throttle the vacuum flow, reduce efficiency and increase cycle times.
Are venturi vacuum generators noisy?
The short answer is yes. When you dramatically accelerate air flow across a nozzle a sound is generated. Standard exhaust air silencers can cause a back pressure and again disturb the nozzle efficiency, particularly if they are allowed to become dirty, soiled and blocked. Instead, users should look out for open flow silencers, which absorb the sound without causing any back pressure, and don't lose efficiency over time.
Is air contamination a problem?
Without wishing to teach anyone to suck eggs, with pneumatics it's always a good idea ensure that you have a clean air supply. However, having said that, venturi vacuum generators - especially the single stage types - are relatively unsusceptible to contamination, the nozzle flow is self cleansing and there are no moving parts. In very dusty environments, it is possible to periodically back pressure a vacuum generator if need be, to blow away any particularly large particles.
Are venturi vacuum generators difficult to design-in?
Quite the opposite. They are low in weight and very compact, enabling them to be mounted at the point of need, directly on the end effector. What's more, this allows use of very short vacuum tube lengths - which helps minimise time-to-vacuum - and increases overall system operating efficiency. The calculations involved in choosing the correct type of venturi vacuum generator are reasonably straightforward, and there are a number of helpful guides on the market. Festo, for example, offers a free software program to help users select the most appropriate vacuum components for their application. You can download it from our website at www.festo.com/gb/vacuumsoftware.
For original equipment manufacturers, Festo can supply a whole range of precision venturi nozzles for direct integration within the manufacturers' own mechanical components. These can dramatically reduce the space needed, and provide a very neat and effective way of integrating components.
29 June 2006
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