When planning your office setup, it’s important to take into account the strength of your dental vacuum pump. When measuring vacuum strength, a term that's mentioned a lot is “Hg.” But where does the term “Hg” come from, what exactly does it mean, and how does it relate to dentistry?

Check out these 5 facts about Hg and vacuum pump strength.

Fact 1: Hg = Mercury

Hg refers to the 80th element of the periodic table, mercury.

Fact 2: Hg is a Unit of Measurement

Simply put, Hg is the unit of measurement for the work output of a particular vacuum. It is described as the measurement of "inches of mercury", which translates to millimeters of mercury for the metric system.

This measurement is a comparison between the barometric pressure and the pressure within the vacuum. The difference is the measurement itself. For example, if the mercury rises 3", the vacuum has 3" Hg of pressure, or 3” Hg less pressure than barometric pressure.

Fact 3: Hg Can Be Measured in 2 Different Ways

The first way to measure Hg is known as the Hg gauge (HgV). The scale goes from 0" Hg (atmospheric pressure) to 29.92" Hg (perfect vacuum).

The second way to measure Hg is the Hg absolute (HgA). This measurement is the reverse of the Hg gauge. In this measurement, the gauge starts 29.92" Hg for atmospheric pressure, and 0" Hg is perfect vacuum.

Fact 4: The Hg Measurement was Invented because of Galileo

Yes, you read that right. A contemporary of Galileo, Evangelista Torricelli, invented the Hg measurement in the 1640s to help Galileo study vacuums.

Galileo’s experiments involved filling a tube partway with mercury, turning it upside down with the open end in a bowl of mercury, and noting how far the mercury in the tube fell before the vacuum inside the tube prevented any additional mercury from coming out.

Fact 5: In Dentistry, Hg is Used to Determine the Number of Pump Users

The practical dental application of the Hg measurement is determining the efficiency and power of vacuum pumps. Hg tells us the number of users who can simultaneously use the same vacuum pump.

Most pumps can support a number of users equal to half the Hg rating.
 
If the pump produces enough Hg, the office will have enough suction to evacuate all necessary materials even when fully staffed. However, if the pump isn't strong enough to evacuate all materials, it's time to upgrade.

Further Reading

And those are the basics on how Hg strength relates to dental vacuum pumps.

If you have more questions about vac pumps, check out our Vacuum Pump FAQ.

Or, if you’re looking for tips on purchasing a new or replacement vacuum pump for your office, here are 4 things to consider when buying a dental vacuum pump.