What are vacuum pumps and vacuum chambers and how do they create low pressure ?

At Double Stone Steel, one of the most crucial pieces of equipment we rely on to produce coloured stainless steel is a vacuum chamber. We use vacuum chambers in all our plants worldwide and, to be honest, we forget just what a marvel of engineering these chambers are. We take all our vacuum chambers and the immense engineering they contain for granted.

A vacuum chamber is an enclosure made from a solid material such as stainless steel and pumps are attached to the chamber to allow the atmosphere inside the chamber to be pumped out. Today, we understand that there is no such thing as a perfect vacuum, even in outer space there is one atom per cubic centimetre.

Invention of the vacuum pump

The British polymath, Robert Hooke, was born in 1635 in the village of Freshwater on the Isle of Wight. He was the son of the local clergyman and when his father died in 1648, Hooke used the £40 he was left in the Will to further his education in London. He bought an apprenticeship and, after proving himself to be an apt student, was able to enter Westminster School and immerse himself in his love of science.

Posthumous portrait of Robert Hooke by Rita Greer (2004) depicted with a spring, pocket watch and map of London which he helped to rebuild after the Great Fire in 1666.

Posthumous portrait of Robert Hooke by Rita Greer (2004) depicted with a spring, pocket watch and map of London which he helped to rebuild after the Great Fire in 1666.

Hooke made tremendously important contributions to the science of timekeeping, being intimately involved in the advances of the age. He invented the anchor escapement which introduced pendulums to regulate clocks, and is still used in watches today. He also developed the balance spring, which meant for the first time a portable timepiece could keep time with reasonable accuracy.

Robert Hooke was also an architect. He was Christopher Wren’s chief assistant, and in this capacity, he helped Wren rebuild London after the Great Fire in 1666. He worked on many famous buildings including the Monument to the fire in Pudding Lane and Wren’s masterpiece, St Paul’s Cathedral.

In 1671, while he was working as a researcher for the great Robert Boyle, Hooke invented the first vacuum pump along with the first altitude or hypobaric chamber. This vacuum chamber allowed Hooke to carry out experiments on himself at an artificial pressure equivalent to approximately 2.5 kilometres above sea level.

Hooke was also an early adopter of microscopes, put forward the theory that combustion required air and was an early proponent of gravity. British historian, Allan Chapman described Hooke as England’s “Leonardo”. This prolific scientist, inventor and architect died in 1703 at the age of 67.

Microscope manufactured by Christopher Cock of London for Robert Hooke in 1665. Hooke inspired the use of microscopes for scientific exploration with his book, Micrographia.

Microscope manufactured by Christopher Cock of London for Robert Hooke in 1665. Hooke inspired the use of microscopes for scientific exploration with his book, Micrographia.

Creating low pressure vacuums

Let’s do a simple thought-experiment. Imagine we have a container that holds one cubic metre of air and the container is completely sealed so nothing can get in or out. Next, we stretch the container until it is two cubic meters. We have managed to double the size of our container so the air pressure inside the container will fall by half.

As the air pressure has halved, we can understand that the distance between each air molecules in our container has now doubled. If we double the size of our container again to four cubic metres, the pressure will again fall by half, and the distance between the molecules will double again.

It is the air molecules forced into and contained in a space that gives us air pressure. Think of a bicycle tyre or a scuba lung.

To get down to only 26,000 molecules per cubic centimetre in our container – the very low pressures achievable in a modern vacuum chamber – we would have to increase the size dramatically. We would need to increase the size of our container to a staggering 970,299 cubic kilometres – that is more than 200 times the volume of the Grand Canyon. If the air molecules were the size of a grain of wheat, they would be approximately 1500 meters apart. That is low pressure!

Vacuum chambers at Double Stone Steel

In each of Double Stone Steel’s vacuum chambers, we can approach these low pressures between 12 to 24 times per day. The vacuum chambers are reliable and relentless.

The world’s largest vacuum chamber at Nasa’s Space Power Facility in Ohio. The chamber has a volume of 22,653 m³, measuring 30.5m in diameter and 37.2 m high.

The world’s largest vacuum chamber at Nasa’s Space Power Facility in Ohio. The chamber has a volume of 22,653 m³, measuring 30.5m in diameter and 37.2 m high.

Double Stone Steel’s vacuum chambers are engineered to withstand all the immense stresses involved. The lids alone on our largest chambers weigh over two tons and the walls are over 100mm thick.

When we take the lid off our larger vacuum chambers at sea level, there is approximately 2.65 x 10 to the power of 19 or an astonishing 26,500,000,000,000,000,000 (256 quintillion) molecules in every cubic centimetre of air. The chambers are 19m³ so that is 503 500 000 000 000 000 000 000 000 (503 septillion) molecules in total.

To find out more on the vacuum process that Double Stone Steel uses to create its PVD product see The basics of Physical Vapour Deposition

Double Stone Steel PVD vacuum chamber Wimbledon, London, UK

Double Stone Steel PVD vacuum chamber Wimbledon, London, UK

By Daniel Groves
Richard Storer-Adam is MD of Double Stone Steel Ltd which fabricates PVD coloured stainless steel. Richard’s background is in design and project management, he lives in Spain and travels extensively writing about writes about architecture and sculpture in Richard is passionately interested in sculpture.