Selecting a Proper Vacuum Pump for your Acrylic Vacuum Chamber

In this article we will talk about Vacuum Pumps - but also about other equipment which is used to produce vacuum inside a closed system or chamber. We will talk about the workings of a vacuum pump, vacuum generation, pump down, pump horsepower. This article is intended to provide you a practical guide which should help you select the appropriate vacuum pump for your system.

Vacuum Pumps

In real simple laymen terms, a vacuum pump is a device which is capable of producing vacuum. A vacuum is a condition where the pressure is lower than the ambient pressure; hence there is a pressure difference between two systems. People often make the mistake of confusing a vacuum to an air pull, where in reality, a pull is the result of vacuum and not the condition itself. The "air pull" is created because the higher pressure system (ambient air) is flowing towards the lower pressure system (vacuum) due to pressure difference.

According to the Ideal Gas Law, the pressure is proportional to the number of molecules in an enclosed system. This means that a vacuum is created by removing the air molecules from an enclosed system such as an Acrylic Vacuum Chambers.

Classification of Vacuum Pumps

It would not be an overstatement to say that vacuum pumps come in all shapes and sizes and that we could go into pages and pages describing the workings of each type. However, and for practical reasons, we will keep this short and concise and concentrate only on pumps that are ideal for Acrylic Vacuum Chambers.

Rotary Vane Pump

Rotary Vane Pump Connected to an acrylic vacuum chamber
Rotary Vane Pump Connected to an acrylic vacuum chamber

A rotary vane pump is the most popular vacuum pump used today for various vacuum applications. There are literally hundreds of different vacuum pumps out there. Oil sealed Rotary Vane Vacuum pump are either one (single) stage or two (dual) stage.

Single Stage Rotary Vane Pump
The single stage vacuum pump has an eccentric rotor which is oil immersed. When the rotor turns, the vanes act as seals, by gliding against the inside of the housing wall and creating a positive displacement or vacuum. The ultimate vacuum rating of a single stage rotary vane vacuum pump is around 0.015 Torr (15 microns).

Dual Stage Rotary Vane Pump
A dual stage rotary vane pump operates in two stages. The first stage is the pump down stage while the second stage is the exhaust stage. This enables the dual stage vac pump to perform better at higher vacuums. In fact, the dual stage pump outperforms its single stage counterpart the higher the vacuum is - the higher the vacuum the better the outperformance. Additionally, the dual stage pump will go down to 0.001 Torr or 1 micron.

Advantages of Rotary Vane Pumps

The main advantage is that rotary vane pumps are very popular and common and can be purchased anywhere for any price. In addition, a rotary vane pump only requires electricity to run - all you have to do is plug it into electricity, flip a switch, and voila, you got yourself some pretty decent vacuum. Even a cheap two stage pump can reach vacuum levels of 100 microns; which is pretty impressive. The higher end models can reach 1 micron. A rotary vane pump is easy to maintain and to service.

Disadvantages of Rotary Vane Pumps

Rotary vane vacuum pumps can be somewhat loud. Vacuum pump oil can sometimes create a mess and be an inconvenience because you will have to maintain your pump and change the pump oil as needed. High end rotary vane pump models can cost you thousands of dollars while the cheap ones will go out on you after a few months use.

Aspirator Vacuum Pump - Venturi Pump

venturi vacuum pump schematics
Venturi Vacuum Pump Schematics

An aspirator vacuum pump is a device which produces vacuum by Ideal Gas Law. A Venturi effect produces a pressure difference by constraining, or slowing down the air molecules in a pipe, or system. This slowing down of air molecules causes the pressure to increase, if you connect an orifice to the larger diameter pipe and another orifice to the smaller diameter pipe, you essentially create a Venturi Pump - as simple as that.

Advantages of a Venturi Pump

The main advantage of a Venturi pump is that is it fairly cheap, "indestructible", and low maintenance - it is essentially a piece of metal which when hooked up to an air line, creates a vacuum.

Disadvantages of Venturi Pumps

The main disadvantage of the Venturi pump is that it requires compressed air to operate. Another disadvantage of a Venturi Pump is that fact that ultimate vacuum cannot go down below 40 Torr (40,000 micron) absolute pressure.

Sorption Vacuum Pump

A Sorption pump is made of an air absorbing material such Zeolite which is a porous material that has cavities small enough to trap air molecules such as Nitrogen, Oxygen, etc... The absorbing material is encased in a vessel. For a sorption pump to be effective, it must be cooled to lower, cryogenic temperatures which means that the vessel has to be immersed into a liquid nitrogen bath.

sorption vacuum pump schematics
Sorption Vacuum Pump Schematics

The best way to describe a sorption pump would be to imagine a bucket of water and a sponge; sponge representing absorbing material, water representing air, and the bucket representing your vacuum chamber. By dipping the sponge into the bucket, you essentially remove water from the bucket, hence creating vacuum. Sorption pumps usually go down to 0.1 Torr. Some types of specially designed Cryo-Sorption Pumps have the ability to go down to 0.00001 Torr or 0.01 micron.

Advantages of a Sorption Vacuum Pump

The main advantage of a sorption pump is that it has no moving parts and is essentially free of contaminants such as pump oil or debris. This pump is very clean and makes it an ideal choice where system cleanliness and being contamination free is critical.

Disadvantages of a Sorption Vacuum Pump

Obviously the main disadvantage of as sorption pump is the requirement for liquid nitrogen. Another disadvantage is that noble gases are not well absorbed by this type of pump. Lastly a sorption pump must be regenerated which means that it must be heated back up to room temperature in order to release the air molecules from the porous material once it gets saturated with air molecules.

How to Select your Vacuum Pump

1. The Ultimate Vacuum: This may be confusing because some list it as Torr, mbar, in Hg, etc. Make sure you compare units to units, apples to apples, oranges to oranges. The ultimate vacuum is determined by the pump type and design, whether it is an aspirator, a sorption, a single stage or a dual stage rotary vane pump.

2. Pump Flow Rate: Again, some list it as liters per minute, cubic feet per minute (CFM), or cubic meters per hour. The larger the chamber, the higher the flow rate you will need in order to pull your vacuum to a certain level. Obviously a pump with similar power but larger flow rate will be able to pull vacuum quicker. But, the flow rate decreases as the vacuum level increases that is because the more air is pulled, the harder it becomes for a pump to pull more air.

3. Pump Power: This is important because as you go into higher vacuum, higher power is required to pull the air which is now sticking to the walls of the chamber away from that wall. Imagine water droplets being removed with a vacuum cleaner. You can remove the big drops pretty easily, the smaller ones stick to the wall much stronger which is why you need a more powerful pump. The same thing happens to the vacuum chamber but instead of water you are pulling air molecules from the volume but mostly air molecules sticking on the wall.

4. Pump Quality: This is a very important question that you must ask yourself. It will require you to estimate how you are planning to use your pump. If you intend to use your pump 10 hours per day, 7 days a week, you may want to consider going with a continuous duty vacuum pump as these will last you longer and will run you better for a much longer time. There are drawbacks to getting a vacuum pump from for a couple of hundred bucks because you will be getting a lower quality pump with a much shorter service life. In addition, it is close to impossible to find spare parts or rebuilt kits for the cheaper vacuum pumps. So be aware that even though you may think that you saved yourself $800 by going with a cheap vacuum pump you purchased for $300. In fact, this pump could go out on you after 3 months and cost you much more in the long run - but that all depends on how you intend to use your pump.

5. Your Budged: Perhaps this should have been placed on top of the list; however, since we are talking about functionality and not finances, it was placed last on this list. Nonetheless, the cost of your pump is important. You want to get the best bang for your buck and as you have already noticed, the price of a vacuum pump can really start to rack up as you start to add features, specifications, and requirements.

Rule of Thumb for Selecting the appropriate Vacuum Pump for your Acrylic Vacuum Chamber

Plexiglass Vacuum Chmaber, Cube, 8 inch inside dimensions.jpg
Plexiglass Vacuum Chmaber, Cube, 8 inch inside dimensions

Generally speaking, the highest vacuum that you should expect in an acrylic vacuum chamber is about 0.1 Torr; you may go lower if you use a more powerful pump, but as stated above, acrylic is intended for low vacuum applications.

Vacuum Pump for an Acrylic Vacuum Chamber
The vacuum pump is the single most determinant of the vacuum levels you will achieve in your chamber. The air flow as well as the vacuum pump power will determine how fast and how high of a vacuum you will be able to pull. A good rule of thumb is to take the vacuum volume of the chamber and multiply that by 2.5. This will give you the CFM requirements of your vacuum pump.

Quick Vacuum Pump Requirement Calculation
For chamber volume of 1 cubic foot (28.13 Liters) or less, it is recommended to use a vacuum pump in the 1/4 HP to a 1/3 HP range and a flow rate of 1.5 cubic feet per minute (CFM) to 3.0 CFM. [Note: 1 cubic meter per hour is equal to 0.588577779 cubic feet per minute]. Higher vacuum volume will require a more powerful and a more flowing pump. Even though the pumps described in the paragraph above should work OK, it is recommended to implement a stronger pump. Pumps in the 1/2 HP to 3/4 HP and 3 CFM to 5 CFM will work for this range. For optimal performance, this vacuum volume will require pumps which are in the 3/4 HP and higher range and 7 CFM or higher.

You should reference the table below as a guide for your pump selection. Keep in mind that the table below is more of a rule of thumb than a gospel - you should contact us if you are not entirely sure which pump to use for your system application.

Acrylic Chamber Volume (cubic feet) Recommended Vacuum Pump CFM Recommended Vacuum Pump Horsepower
Less than 1 3.0 or less 0.25 (1/4) HP or more
1 to 2 3.0 to 5.0 0.33 (1/3) HP or more
2 to 4 5.0 to 7.0 0.50 (1/2) HP or more
4 or more 7.0 or more 0.75 (3/4) HP or more
NOTE: Table is for reference only. A pump with lower CFM or horsepower will get the job done as well but it may take longer to pump down to the desired vacuum levels.

Recommended Vacuum pump for Clear Vacuum Chamber

A Rotary Vane pump is the way to go in 99% of all systems involving an acrylic vac chamber - as simple as that. Just doing a quick search on rotary vane pumps, you will find that your selection is endless.

The choice of vacuum pump is completely up to you. You must however balance your budged with performance because, as with all things in life, performance comes at a price. Depending on what vacuum level you intend to get and how fast you are looking to get down to a certain vacuum level you should consider the pumps below.

Purchase Our Acrylic Vacuum Chambers Here

Contact us if you need help selecting your vacuum pump

We have done this long enough to know which pump will work with which acrylic vacuum chamber. You are very welcome to contact us with questions regarding vacuum pumps. And even though we neither carry nor sell vacuum pumps ourselves, we would be happy to assist you with your pump selection.

Copyright © 2018 Sanatron