Figure 1: Vacuum generators
Vacuum generators create a level of vacuum that is required for object handling tasks. These devices create a vacuum either pneumatically using compressed air or electrically using a displacement pump. Electrical generators are often called vacuum pumps.
The main differences between them are:
Vacuum generators are often used in conjunction with vacuum suction cups. A vacuum suction cup is connected to the vacuum generator’s outlet and is what is attached to the object being handled. Read our vacuum suction cup article for more information.
The vacuum generators are generally classified into pneumatic vacuum generators and electric vacuum generators (vacuum pumps).
The pneumatic vacuum generators, also known as vacuum ejectors, uses a pneumatically driven nozzle to generate a vacuum. They are suitable if the application requires short and rapid cycle times. They can be integrated directly into the system due to their lightweight and compact design. Depending upon the number of nozzle pairs, they are divided into single-stage, multi-stage, and compact vacuum generators. The vacuum generator operates based on the Venturi effect.
Figure 2: The Venturi effect: intake (A), vacuum formation (B)
A single-stage vacuum generator consists of a jet nozzle or a Venturi nozzle through which the compressed air is passed. The narrowing of the jet nozzle causes the air to accelerate. As it passes through the narrow nozzle and starts to expand, a vacuum is created at the expanded side. The air is drawn through the inlet and the compressed air exits through the silencer.
A multi-stage vacuum generator has multiple venturi nozzles(A) arranged in a row. The compressed air is supplied through the connection port. This compressed air passes through the several Venturi nozzles. As the vacuum is created, the air is drawn through the inlet (B). The suction rate from the inlet is the total of suction from the individual nozzle of the generator. The multi-stage vacuum generator can provide a much higher suction rate for the same amount of compressed air than the single-stage vacuum generators.
Figure 3: Multi-stage vacuum generator
The compact vacuum generators have integrated valve with system monitoring technology. This generator makes it easier to control the pick-up and blow-off without the aid of any external valve. They are generally used for completely automated handling systems.
Figure 4: Single stage (left), multi-stage (middle), and compact vacuum generator (right)
Vacuum generators have some clear advantages over vacuum pumps. The most important ones are listed below:
Generators have some drawbacks too. Compressed air must be available at the location. Furthermore, compressed air is relatively expensive, which increases the total cost in the long run.
Vacuum generators are mainly used in pick and place robots in virtually all industries. A few examples are feeder applications in the automotive industry, end-of-line applications such as food packaging, etc.
The electric vacuum generators, also known as vacuum pumps, are used when high suction capacity is required or when there is no availability of compressed air. The vacuum pumps operate by removing the air molecules from the vacuum chamber. It consists of an eccentrically mounted rotary impeller with carbon blades (A). The impeller is pressed against the wall of the housing by the centrifugal force which provides an excellent seal. The size of each chamber (B) changes with the rotation of the impeller. As the chamber becomes larger in size, the air inside it expands. This causes the pressure to drop in the chamber creating a partial vacuum. The air is thus drawn in, compressed, and expelled through the outlet. The high compression factor helps the vacuum pump generate a high vacuum and provide high suction capacity.
Figure 5: Vacuum pumps: carbon blades (A), chambers (B)
The main advantages of vacuum pumps are:
Drawbacks are that they are less simple than vacuum generators and larger in size with a higher initial investment.
Some examples of applications:
The main selection criteria for vacuum generators are listed in the sections below.
We recommend unlubricated air. The reason is that dirt particles can settle in the vacuum generator and silencer when you use lubrication. This impairs the performance of the device.
Vacuum generators create a vacuum level that is required for lifting tasks.
You can create a vacuum using a venturi nozzle. When the air flows through, the air is accelerated and compressed. After passing the constriction, the accelerated air expands, and a vacuum is created.