Vacuum generators - How they work
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.
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The main differences between them are:
- Vacuum generator builds up a vacuum quickly and have short cycle times. Thanks to their simple and compact design, they can be integrated directly into the system close to the vacuum suction cups.
- Vacuum pumps can create very high suction rates and high levels of vacuum when needed. Since the vacuum is created using an electric motor, they are suited for applications where compressed air is not available.
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.
Table of Contents
Types of vacuum generator
The vacuum generators are generally classified into pneumatic vacuum generators and electric vacuum generators (vacuum pumps).
Pneumatic vacuum generator
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)
Single-stage
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.
Multi-stage
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
Compact
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)
Pros and cons of vacuum generators
Vacuum generators have some clear advantages over vacuum pumps. The most important ones are listed below:
- Generators are very compact and low-weight, which allows them to be installed close to the application.
- A vacuum is generated very fast.
- There are no moving parts, which results in low wear and practically no maintenance.
- No heat is generated.
- Relatively low initial investment.
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.
Typical areas of application
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.
Electric vacuum generator (vacuum pump)
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)
Pros and cons of vacuum pumps
The main advantages of vacuum pumps are:
- They can create a very high vacuum, combined with a high evacuation volume.
- One vacuum pump can be used as a central location to generate a vacuum for multiple locations.
- Generally, they require little maintenance.
- No compressed air system is required.
Drawbacks are that they are less simple than vacuum generators and larger in size with a higher initial investment.
Typical areas of application
Some examples of applications:
- Central vacuum generator for gantry systems
- Packaging machinery
Selection criteria
The main selection criteria for vacuum generators are listed in the sections below.
- Suction rate
- You can compare vacuum generators on their suction rate. This is usually given in m3/h, l/min, or cfm. The values are based on standard conditions, which means ambient temperature (20 °C) and ambient pressure at sea level (1013 mbar).
- The maximum suction rate is defined as the maximum flow rate that the vacuum generator evacuates from the environment. This means free flow, so the flow rate when a workpiece is picked up will be lower.
- The required suction rate is a result of the internal volume of the suction pads and the piping. Furthermore, the handling of porous materials, such as cardboard, requires higher suction rates than air-tight materials. For these applications, a high suction rate is more important than a high vacuum level.
- Vacuum level
- The vacuum level is usually given as a percentage or relative value. The vacuum is specified in relation to the ambient pressure. A vacuum level of 80% means that the pressure is 80% lower than the ambient pressure. If the ambient air pressure is 1013 mbar absolute pressure (14.7 psi), an 80% vacuum means an absolute vacuum pressure of 202 mbar.
- Evacuation time
- Time in seconds that is required to create a specific vacuum level.
- Air consumption
- This is the consumption of compressed air (in l/min or scfm) by the generator to generate a specific vacuum level.
- Operation
- Depending upon the requirement for your application, vacuum generators can be used pneumatically or electrically. An electric generator is suitable for application where compressed air is not available.
FAQ
Do vacuum generators require unlubricated compressed air?
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.
What does a vacuum generator do?
Vacuum generators create a vacuum level that is required for lifting tasks.
How do you make a vacuum with compressed air?
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.
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