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Basic practical facts about types and operation of vacuum pumps

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Posted July 3, 2019

Vacuum pumps have been around the mid-1600s; they have been used for many reasons and upgraded several times since then. But what exactly is the function of a vacuum pump?

A vacuum pump is a tool or device used to ‘suck out’ gas molecules from a sealed mass and leaves behind a partial vacuum (a space without any matter). The simplest example of usage would be someone travelling with a bag of toiletries but does not want the air in the bag to take up space.

Image credit: Pixabay via Pexels (Pexels licence)

Image credit: Pixabay via Pexels (Pexels licence)

A vacuum pump in this case would be especially useful as it would take out all the air (gas molecules) and leave the partial vacuum for the toiletries within the bag. Although this is a very basic example, vacuum pumps are used for many different reasons and have several different jobs. Below are some things no one tells you about the different types of vacuum pumps.

There are Three Main Types of Vacuum Pumps:

A) Positive Displacement Vacuum Pumps (piston pumps, diaphragm pumps)

B) Momentum Transfer Vacuum Pumps (turbopumps, diffusion pump)

C) Entrapment Vacuum Pumps (Cryopumps, sorption pump)

The pumps listed after each category are not the only ones which fall under the umbrella of vacuum pumps. However, these are some of the most common ones.

Positive Displacement Vacuum Pumps

So, what is a positive displacement pump? A positive displacement pump moves fluid by repeatedly surrounding a volume of fixed mass and moving the fluid ‘mechanically’ through a system.

There are two different types of positive displacement pumps: reciprocating and rotary. Reciprocating positive displacement pumps, which are most common, work by repeating the movements back and forth called strokes, these use pistons, plungers, and diaphragms. Piston pumps have two main phases, suction phase and the compression phase. The suction phase is when the first ‘stroke’ constructs a vacuum, creates an inlet valve (a valve in which allows for fluid to be drawn into the cylinder), then proceeds to close the outlet valve (a valve that controls the escaped fluid) and takes fluid into the ‘piston chamber’ (where the pistons move). In the compression phase, the piston reverses and the inlet valve closes, and the outlet valve opens, which then allows the fluid to be discharged.

The diaphragm pump uses a malleable membrane to move fluid, instead of a piston. The diaphragm expands and the chamber which pumps the fluid also expands, allowing for fluid to be drawn within the pump. Diaphragm pumps also have a compression phase where it decreases the volume of the chamber and takes out some fluid. The best feature about diaphragm pumps is that they are sealed off well, which allows them to be especially useful when pumping dangerous fluids.

Momentum Transfer Vacuum Pumps

A momentum transfer vacuum pump is a type of pump which works alongside a positive displacement pump. Although a positive displacement pump can work without a momentum transfer pump, the opposite is not possible. The latter works as follows: gas molecules are taken from the ‘vacuum’ side to the ‘exhaust’ side. In order for that to happen, a positive displacement pump maintains the pressure and reduces it to a rate that is plausible to work with. The two types of pumps which fall under this are diffusion pumps and turbomolecular pumps, with the latter being more common.

Entrapment Vacuum Pumps

An entrapment pump, which is most commonly a cryopump, uses cold temperatures to turn the gases into a solid or absorbed state. A ‘chemical’ pump then reacts with these gases to make a residue and then ionizes the gases to solid substances.

Vacuum Pumps Need Maintenance

Similar to all devices, vacuum pumps need maintenance. According to a comment from Provac Sales, modern vacuum pumps are designed to be properly maintained in a timely manner, so never hesitate to contact the professionals to keep your equipment running without failures. But there are things you can do to make that help more efficiently.

The first thing you must do is document everything, from oils to other fluids, to regular versus irregular vibration, and so on and so forth. Secondly, depending on the type of vacuum pump, it may need oil changes and inspections, at least monthly. You must also check for any oil leakage and seals, which in case of breakage should be replaced immediately. If you have documented everything in the beginning, then your last maintenance tip is to cross-check whether the pump works as it first arrived or not.

Image credit: Jesper Markward Olsen via freeimages.com (FreeImages.com Content License License)

Image credit: Jesper Markward Olsen via Freeimages.com (FreeImages.com Content License License)

The Right Fit for You

When choosing a vacuum pump, you must know which purpose you need it for. Vacuum pumps are used in machinery such as cars, as well as on their own in chemical labs for example. The first step is to jot down why you need it, and read the pros and cons of the type of pump available for your kind of work. At the end of the day, you want something that makes your life easier.

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