The Basics of Vacuum Technology
Air-powered or pneumatic vacuum technology is one of the most misunderstood technologies in automation. Since compressed air is one of the most widely available power sources within manufacturing industries, it’s easy to add vacuum to an operation.
Using the venturi effect, air-powered vacuum is produced by forcing compressed air through a limiting orifice (nozzle). As the air exits the orifice, it expands and then increases in velocity to supersonic speeds before entering the diffuser. This creates a negative pressure (vacuum) at the vacuum inlet port located between the nozzle and the diffuser.
There are various types of venturi vacuum generators all with unique functions for different applications – that’s why it’s important to select the right vacuum generator and vacuum cups for each application to create an economic and efficient system design.
Vacuum applications all have variables that need to be considered; a major consideration is understanding how the combination of air consumption – vacuum level, force, flow, and cycle times – all interact to achieve the desired results.
Much like a vacuum cleaner at home, the vacuum generator will draw in anything near the vacuum port, including ambient air, dirt, and debris. Depending on the style of generator, dirt and debris can clog the vacuum generator. Single stage generators are far less susceptible to clogging, which reduces or eliminates maintenance requirements, but they are less efficient at low vacuum and tend to blow the debris out the exhaust port. On the other hand, multi-stage generators can consume less air but require filters to reduce clogging. The addition of filters adds required maintenance. When selecting a venturi vacuum generator, consideration should be given to cost of air versus cost of maintenance.
How do you properly size a venturi vacuum system for a basic pick and place application? The equation used for sizing a pneumatic cylinder similarly applies to sizing a vacuum system: the force required at the piston rod is equal to the pressure times the area (F=PxA). The force (or weight of an object) that a vacuum system can pick up is determined by the area of the vacuum cup multiplied by the vacuum level of the generator expressed in PSI.
For example, when using the (F=PxA) equation, a 2” diameter vacuum cup has an area of 3.14 in2 ; if the vacuum generator produces 28”Hg (or 14 PSI), the holding force of the vacuum cup would be 14 PSI x 3.14 in2 , which equals 43.96 lbs of holding force.
Emphasis should be placed on the vacuum flow path beginning with the object being handled or vessel being evacuated and ending at the vacuum source to ensure you have an efficient vacuum system. Improper sizing of the system components is one of the most common vacuum system design flaws known in the field. Vacuum effectiveness can easily be reduced by restrictions from tubing, valves, fittings, and other components.
To check that your system isn’t restricting any vacuum flow, place a vacuum gauge at the top of the generator. If the gauge reads vacuum when nothing is connected to the suction cup or a vessel is not attached, then the system is restricting flow. If the system is not working properly (i.e., not picking up a porous object or evacuating a vessel fast enough), using a larger vacuum generator will not fix the system until the flow path size is increased. In certain applications where restrictions cannot be eliminated, it is best to consider using a generator with a higher vacuum level in order to provide the fastest evacuation possible.
Contact us to receive more information and guidance on how to properly integrate vacuum technology into your system as well as the different types of vacuum generators, cups, and accessories that can solve your automation issues. If we can’t answer your questions, we can connect you to our vacuum experts partners.