What Exactly is Vacuum Pressure?

Vacuum is nothing. The word vacuum is defined as “a space entirely devoid of matter”. Taken literally this is something so physically difficult to achieve. Most scientists and physicists say it’s impossible. The only natural vacuum that we know of in the universe is space – and technically that’s not even a real vacuum since there are many other things in it (things like planets and even small particles). What this means is that ‘complete’ or ‘100% vacuum’ is only theoretical.

Achieving Small Amounts of Vacuum

It’s pretty easy to create a small amount of vacuum. For instance: the noise created by clapping one’s hands together actually results from the creation and subsequent exhaustion of a small amount of vacuum. To maintain this vacuum without exhausting it, however, is much more difficult.

Aristotle actually noticed this thousands of years ago. He noted that “nature abhors a vacuum” essentially predicting what modern advanced scientific techniques and systems would prove much later. Defining vacuum properly requires a bit of a dive into some basic physics and scales of measurement. These are simply measures of pressure. The physics part of this becomes very complicated very quickly – so bear with me for this next part.

3 Systems of Measurement for Vacuum

There are 3 systems of measurement for Vacuum: Torr, mbar, and Pa. There are a few reasons why these three scales exist, but we will keep it simple for now. Torr is widely used in the vacuum industry and is sometimes referred to as “millimeters of mercury” or “inches of mercury”[1].

Mbar is used when referring to atmospheric pressure, and subsequently is the scale used in meteorology science.

PA is the official SI[2] unit for vacuum pressure and as a result it is widely used in the study of physical sciences. Most measurements are taken in mbar, so we will try to stick to that when describing various pressures.  Here’s a handy scale to put things in perspective for the next part.

Getting Your Head Around Vacuum Pressure

To help with defining vacuum, let’s get an idea of how much vacuum is present in some everyday things.

1 bar is roughly equal to earths atmospheric pressure at sea level, and an mbar is a thousandth of a bar. A good home use vacuum cleaner may pull around 85 inches of water. This is equal to about 6.2 inches of mercury or roughly 209 mbar. A good industrial vacuum pump, like the rotary vane ones we make here at Fruitland, can maintain 28.5 inches of mercury. Which is roughly 965 mbar – which is around 96% of a perfect vacuum!

Lastly, a small compressor used inflate an air mattress has a vacuum capacity of roughly 500 mbar depending on the design. It is worth noting at this point that the best natural example of vacuum we can observe in this universe is space, and it becomes more vacuous the farther away from planets you go. The pressure of space at 50km from earth is about 10^–3 mbar and about 10^–6 mbar at 170 km away. That is roughly 0.000001 of a thousandth of an atmosphere – that’s very vacuous!

Just for fun -the sparsest example of distant space has roughly 1 particle per cubic meter in it, and the best ‘vacuum’ ever made here on earth (at the LHC at CERN[3]) has around 1000 particles per cubic cm (much denser). Even intergalactic space isn’t a true vacuum because there’s particles floating around. In space the presence of something like a photonic particle (light) or energy waves from background radiation would negate the existence of a vacuum as its defined.

Understanding Vacuum Pressure Science

Obtaining and understanding vacuum and advanced vacuum systems is a key part of some of the most complex scientific inquiries known to humans. For instance: the LHC (Large Hadron Collider) in Switzerland currently boasts the largest and most advanced vacuum system in the world. The experiments that the scientists at the LHC perform are so exact that most of them need to be encased or assisted by advanced vacuum systems to, as much as possible, prevent the presence of other particles which may skew results.

What all of this means is that any ‘vacuum’ here on earth is imperfect and temporary at best. When we talk about vacuum in industry  – we’re really talking about changes in pressure, which when harnessed as desired, can-do loads of different things for different reasons. The focus in industry revolves around ‘recovery time’ and maintaining consistent vacuum or replenishing that vacuum as fast as possible when its exhausted. In the next blog we will focus more on how a vacuum pump creates vacuum – and take a dive in to some of the variations of pumps and systems used in the market today.

Further Reading, sources, and references.

• https://en.wikipedia.org/wiki/Vacuum
• https://en.wikipedia.org/wiki/Atmospheric_pressure
• https://en.wikipedia.org/wiki/International_System_of_Units
• https://solarmfg.com/wp-content/uploads/2016/02/Understanding-Vacuum-9.pdf
  https://en.wikipedia.org/wiki/General_Conference_on_Weights_and_Measures
• https://www.quora.com/Is-it-possible-to-create-an-absolute-vacuum
• https://guide.directindustry.com/choosing-the-right-vacuum-pump/
• https://en.wikipedia.org/wiki/Evangelista_Torricelli
• https://en.wikipedia.org/wiki/Pascal_(unit)

[1] Thank you USA.

[2] SI is the International System of Units, the internationally accepted standards of measurement throughout the world.

[3]LHC (Large Hadron Collider) CERN (European Council for Nuclear Research)