How do I choose a vacuum generator?

When choosing a vacuum pump, you must take into account several factors. First of all, your choice should be adapted to your intended use, as this will allow you to determine the technology, lubrication, chemical resistance, vacuum level and necessary flow rate.

The determining factor that should guide your choice of a vacuum pump is the quality and desired vacuum level. There are several types of vacuum: a rough or low vacuum, a high vacuum and an ultrahigh vacuum. The difference between the three lies in the scarcity of the number of molecules obtained, which is measured by the pressure of the residual gases. The weaker the pressure, the more the number of molecules per cm³ is weak. As a result, the vacuum quality is higher.

We refer to:

Vacuum type Maximum pressure (in mbars) Minimum pressure (in mbars) Molecules per cm³ Rough vacuum 1 10-3 1016 – 1013 High vacuum 10-3 10-7 1013 – 109 Ultrahigh vacuum 10-7 10-12 109 – 104

 

You will also have to take into account the following characteristics:

• the pump’s flow rate: the flow rate is related to the draining time of the machine. It is therefore necessary to evaluate the capacity of the vacuum pump to produce both the required pumping speed (volume flow rate) and the mass flow rate according to the process requirements. Generally, the higher the flow rate, the shorter the draining time. The table above shows the number of remaining molecules per cm³ depending on the type of vacuum chosen.
• chemical compatibility: it is necessary to consider the compatibility of the gases used in your application with the chosen vacuum pump by analyzing all possible problems that the device may encounter.
• lubrication: it is essential to ask yourself whether or not it is necessary to lubricate the vacuum pump. A lubricated vacuum pump has greater efficiency and resistance. It does however require very regular maintenance. In a laboratory environment, a dry vacuum pump is preferred.
• maintenance and cost : based on the criteria listed above, it will then be necessary to analyze the frequency of maintenance cycles. This will determine the overall cost of your installation, which must take into account the purchase price as well as the operating and maintenance costs.

EXAIR’s compressed air powered E-Vac single stage vacuum generators are a low cost way create vacuum for many operations including- pick and place, clamping, chucking, alignment, lifting, and many others.

The E-Vac provide instantaneous response and are commonly used for pick and place operations.

EXAIR offers the In-Line and Adjustable style of E-Vacs. Both are compact and easy to mount at point of use. With 18 total models available, there is sure to be one that meets any application.

How to Build An E-Vac System:

Step 1 – Select E-Vac type:

A – Determine if the part to be lifted is porous (Example, cardboard) or non-porous (Example, plastic sheet)

• Porous materials require a low vacuum generator which produces a lower vacuum in exchange for higher vacuum flow which is capable of maintaining a good vacuum level through material that aloows air to flow through itself.
• Non-Porous materials are best suited to use the high vacuum generator which is capable of producing more powerful vacuum for the application.

B – Select a style of E-Vac – In-Line Low Vacuum, In-Line High Vacuum, or Adjustable

• Porous – low vacuum generator, max vacuum = 21″ Hg (71 kPa)
• Non-Porous – high vacuum generator, max vacuum = 27″ Hg (91 kPa)
• Adjustable – max vacuum = 25″ Hg (85 kPa)

Step 2 – Find the weight of the part to be lifted:

Step 3 – Multiply the weight by a vacuum cup safety factor (2 for a horizontal vacuum cup position, and 4 for a sideways vacuum cup position)

Step 4 – Determine the number of cups needed, considering the following:

A – How many cups are needed to evenly distribute the weight for stable lifting and placement.

B – What is the weight that each vacuum cup can lift based on maximum vacuum available?

C – Select the appropriate vacuum cup from the different styles available.

Step 5 – Choose the E-Vac model, considering the entire vacuum system from the E-vac to the part:

A – Number of vacuum cups per E-Vac.

B – Length and size of the vacuum tubing.

C – Vacuum cup size and type.

• The volume of air to evacuate from your vacuum system and the vacuum flow of the E-Vac selected will determine the time it takes to build the lifting vacuum level.
• A lower volume of air in the system and/or higher capacity (SCFM/SLPM) E-Vac will result in faster pick-up times.
• It is difficult to calculate an exact pick-up time.

Example – Sheet of material 3′ x 3′ (0.91m x 0.91 m) that weighs 25 lbs. (11.3 kg). Each sheet is in stack and will be placed on a conveyor.

As you can see, there is a lot to consider when building an E-Vac system. Feel free to contact us and we can help go through the steps.

If you have questions about E-Vacs or any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer
Send me an email
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Twitter: @EXAIR_BB

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