Vacuum Pumps Overview
, by Mike Pabich, 7 min reading time
, by Mike Pabich, 7 min reading time
This post discusses vacuum pumps in depth and covers all related topics from vacuum pump selection, vacuum pump type, vacuum pump maintenance and care, as well as specific vacuum applications. It also includes a list of recommended vacuum pump pairings.
What is a Vacuum Pump?
Vacuum pumps are devices that remove gas molecules from a sealed chamber or container so that the atmosphere inside becomes extremely reduced or non-existant. Vacuum is space void of matter. If you were to leave the Earth's atmosphere, you would quickly find there is no air to breath because outer space is a vacuum. Vacuum has become a valuable tool in the industrial, scientific, and material processing fields for it's ability to create differential pressure zones, imitate deep space, lower boiling points of molecules, and allow temperature differentials not usually achieved at standard atmospheric pressure. The use of vacuum in our industry allows us to do many of the things mentioned above. As you will see from this post, vacuum pumps are not a new technology, and their range and birth have been in use across the world for many years.
Types of Vacuum Pumps
The following is a comprehensive list of vacuum pump types. Many of these pumps are not used in our industry.
- Dry Rotary Lobe
- Dry Screw and Piston
- Dry Scroll
- Dry Semiconducter
- Roots Blower
- Rotary Piston
- Rotary Vane
- Turbo Molecular
We will discuss the main types of vacuum pumps we use in our industry as well as a few deep vacuum pump types that will most likely be in use in the next few years as our industry progresses. As you can see, there are many different types of pumps. Each of these types of pumps work well for specific applications. But for simplicity sake we will discuss the two major types we use in our industry first. These are; rotary vane pumps and diaphragm pumps. We will then discuss a few of the other major pump types that are not as common but are still worth exploring.
Rotary Vane Pumps
Rotary Vane vacuum pumps are the most common types of vacuum pump on the market. This is because they are easily made, have fewer moving parts, and generally allow for a deeper vacuum than other types of pumps. Rotary vane pumps are commonly called oil pumps because they have an oil reservoir. The oil in the reservoir is used to lubricate the moving parts and in some cases, actually helps create the vacuum seal. Many HVAC style pumps are rotary vane pumps. Many rotary vane pumps have multiple stages, and when using a pump you can tell when you enter a second stage because the pump noise will change. This will happen as the pump gets deeper. You can think of this like the gears in a car transmission. As you increase the speed/vacuum, a new gear/stage must be used to continue moving faster/deeper. Rotary vane pumps can range anywhere from 1CFM to 100+CFM. They may cost anywhere from $100 to 10K+. Rotary Vane Pumps are especially helpful for evacuating large spaces such as vacuum ovens. The more air displacement the pump can provide, the faster the vacuum will be pulled. They will also achieve a relatively deep vacuum, which makes them ideal for distillation systems.
Maintenance and care for rotary vane pumps is relatively simple. You should change the oil often. If your vacuum pump oil becomes dark and smelly, change the oil immediately. You want to change the oil before it reaches this point. To keep a rotary vane pump at peak performance, it is recommended to change the oil after each use. Do not let dirty oil sit inside the oil reservoir. The dirty oil could contain corrosive chemicals which might eat away at the interior of the pump. Rotary vane pumps do have to be rebuilt occasionally. If a rebuild is needed, it is recommended to have this done by a professional vacuum servicing company to make sure you do not damage any parts, and put the pump back together correctly. Before each use, run your pump for up to an hour to allow the motor and oil to warm up. This will ensure your pump is pulling at maximum speed and efficiency.
Diaphragm Vacuum Pumps
Diaphragm Vacuum Pumps are another common type of vacuum pump in our industry. They are extremely chemically resistant and do not use oil. These pumps are "oil-less" and most contain PTFE diaphragms to keep harsh chemicals from destroying essential components. They are excellent for applications such as evaporation and filtration. They do not achieve the same depth as rotary vane pumps but, they do not need costly oil changes. Maintenance for diaphragm pumps is even simplier and often not needed. Diaphragm pumps are often extremely quiet and do not emit oil mist like rotary vane pumps do. They often run much cooler compared to rotary vane pumps. They are more expensive though, but the added benefit is less maintenance and oil changes. Having a diaphragm pump for applications such as evaporation and filtration, and also a rotary vane pump for applications such as distillation and vacuum ovens is recommended. Diaphragm pumps are often referred to as 2-head, 4-head, 8-head, etc. As the amount of heads increase, the CFM also increases. Diaphragm pumps generally will not reach the same CFM as rotary vane pumps but, do work for evacuating large spaces.
Dry Scroll Vacuum Pumps
Dry Scroll Vacuum Pumps are not as common but are extremely popular in other industries. These pumps are usually quite expensive but they are considered by many to be "all-in-one" pumps. They have high CFM for evacuting large spaces and they also acheive very good depth for applications like distillation. Dry Scroll pumps can be difficult to maintain and rebuilds are often costly depending on manufacturer. Many dry scroll pumps are extremely loud as well. They are oil-less and chemically resistant though, making them a serious consideration for some users.
Diffusion Pumps and Turbo Molecular Pumps
If you need to get to extreme vacuum depths for applications such as distillation, you will need a diffusion pump or Turbo Molecular Pump. These pumps can achieve vacuum depth deeper than .01 Micron. In fact some pumps can achieve depths of .0000001 micron+. Without discussing to much of the theory behind these pumps, they work based on a pressure differential created between the top and bottom of the pump. A diffusion pump has no moving parts and creates this pressure differential by allowing heated vapor to rise, recondense, and then drop back down creating a low pressure zone at the top of the pump. As the vapor drops back to the bottom it pulls gas molecules with it, spreading the molecules at the top of the pump very thin hence "diffusing" them. A Turbo Molecular Pump works on a similar principle. Inside a Turbo Molecular pump, a set of rotors spin at an extremely high speed (75000+RPM, that's 1200+ RPM per second.) The rotors pull the molecules of gas closer and closer together creating a similar pressure differential as a diffusion pump. Diffusion and Turbo Molecular pumps both need a backing pump. This is a vacuum pump such as a rotary vane pump that pulls the initial vacuum and holds the vessel at a designated level. Once the vacuum is pulled down, the Diffusion or Turbo Molecular pump kicks on and begins to pull even deeper, as the backing pump then pulls the remaining molecules directly out of the Diffusion or Turbo pump. These pumps are often setup as stations which include the backing pump, Diffusion or Turbo Molecular pump, and a computer system to automate the entire process. They may include other pumps and electronic proportioning valves and cathode ion gauges to measure and control vacuum at extreme levels. These pumps are extremely expensive and require extensive maintenance.
Recommended Vacuum Pumps for Specific Applications:
Vacuum Chambers 1 Quart to 3 Gallon: 1-3CFM Single or Dual Stage Rotary Vane Pump
Vacuum Chambers 5+ gallon: 6-21CFM Single or Dual Stage Rotary Vane Pump
Vacuum Ovens .9CF to 1.9CF: 6-10CFM Single or Dual Stage Rotary Vane Pump or 2/4 Head Diaphragm Pump
Vacuum Ovens 3.2CF+: 11CFM-21CFM Single or Dual Stage Rotary Vane Pump or 4/8 Head Diaphragm Pump
Extractors 1lb+: 6-10CFM Single or Dual Stage Rotary Vane Pump or 4 Head Diaphragm Pump
Extractors 5lb+ 11CFM-21CFM Single or Dual Stage Rotary Vane Pump or 4 Head Diaphragm Pump
Rotary Evaporators 2L to 5L: 2 Head Diaphragm Pump
Rotary Evaporators 10L to 20L: 4 head Diaphragm Pump
Rotary Evaporators 50L+: 8 Head Diaphragm Pump
Distillation Systems: 6-21CFM Single or Dual Stage Rotary Vane Pump