Vacuum pressure gauges - how they work

Vacuum gauges measure pressure below atmospheric pressure. Usually atmospheric pressure is set to zero and vacuum pressure is given as a negative value, so -1 barg (-15 psig) means full vacuum.

What is vacuum pressure?

Atmospheric pressure is the standard pressure at sea level and is 101.325 kPa. It is more common to express pressure in bar or psi. Vacuum pressure (Pvac) is expressed as a negative value relative to atmospheric pressure.It is different from absolute pressure (Pabs), which is measured relative to absolute zero. 

Different pressure definitions explained 

• Absolute pressure Pabs: relative to absolute zero.

• Atmospheric pressure Patm: sea level pressure (1.01325 kPa).

•  Gauge pressure Pgauge: relative to atmospheric pressure.

• Vacuum pressure Pvac: measured relative to atmospheric pressure.

How does a vacuum pressure gauge work?

Most pressure gauges use elbows.This tube is called a Bourdon tube.Under the pressure difference between the medium and the atmosphere,the tube deflects slightly.The tube deflection is translated to the needle position on the dial by a mechanism.This design principle is actually the same for ordinary pressure gauges and vacuum pressure gauges.If you want to learn more about the design principles,you can read our full article on pressure gauges.

Most meters are available with bottom connection or rear connection (panel mount).Meters are available in plastic or stainless-steel housings.Plastic is cheaper and corrosion resistant, but more sensitive to shock.They can be analog pressure gauges such as Bourdon tube pressure gauges or digital pressure gauges.

What are typical applications for vacuum gauges?

Vacuum is used in virtually every industry,from pick and place in the automotive industry, food and beverage,manufacturing, pharmaceutical, chemical, marine and more.A vacuum gauge is an important piece of equipment to ensure optimum system performance and safety.They can be used in pick-and-place applications,keeping workplaces free of contaminants,transporting materials, and more.

Absolute pressure gauge

It should be noted that a vacuum pressure gauge and an absolute pressure gauge are not the same thing.Ordinary vacuum gauges measure atmospheric pressure, while absolute pressure gauges measure absolute zero.For this purpose, the meters contain an almost completely evacuated reference chamber. These are high-end products,for example for monitoring vacuum pumps or vacuum packaging machines.

What is the difference between gauge pressure and vacuum pressure?

Both gauge and vacuum pressure are measured relative to atmospheric pressure. The difference is that gauge pressure is higher than atmospheric pressure, while vacuum pressure is lower than atmospheric pressure.