When the term velocity is used in dental suction it should be referring to the speed at which the air is moving through the suction system. The velocity can be very different at many points along the way.

Velocity has a formula: V (velocity) = Volume going through an opening x 114 Size of the opening The volume going through a hole or suction tool is determined by the vacuum level created by the vacuum pump and the size and shape of the hole. A simple chart can be found in the BaseVac web site: www.basevacdental.com

The stronger the vacuum, the faster the air moves and the more volume you get into the system. At a vacuum level of 15’’hg (mercury) the volume moving through the hole is said to have reached critical flow and cannot get any larger with stronger suction. What does increase with stronger suction is the velocity or speed of that fixed volume of air trying to get into the suction nozzle.

Why does velocity matter in dental suction? Velocity has energy and as the air is whizzing around it bangs into things pushing them and carrying them with the flow of air. So the more aggressive the velocity in speed and power, the better able the air stream is at picking up and moving liquids and debris.

It is the extra velocity associated with higher vacuum dental systems (10-20’’hg) that allow low volume systems to compete and excel over systems with a much higher flow capacity.

Predictable science at work, you can only get so much air through a given size hole, how fast you can do it (velocity) with a stronger suction creates the excitement.