Last week we got a better understanding of the suction requirements of a clinic based on open holes and the basics of pump performance High Flow vs. Low-flow. We have an understanding that at 10” of Hg, both High-flow and Low-flow systems theoretically should perform the same. Why then do some work better than others? First, let’s define “better.”
Velocity
Before we explore the answer, we must consider velocity and its effect on vacuum system performance. Velocity is the speed with which a given volume of air can pass through a hole. For a given volume and a fixed diameter hole, the velocity increases proportionally to the increase in vacuum energy. Simply put, a drink cup has a fixed volume. If you suck hard through the straw (vacuum energy) you can empty the cup faster than if you don’t suck hard. The volume stays the same; it just moves faster.
Vacuum pumps with higher suction energy can increase the speed with which air moves through the system if they are allowed to operate at a higher vacuum level. Higher than 10” of Hg. It is understood, the velocity of a given movement of air creates an energy that can be seen as an increase in volume. This may not necessarily be true, for the reason that the volume is determined by the pump capacity. Additional factors, such as hole diameter and vacuum level at intermittent moments in time, will create the induced flow syndrome.
Induced flow is the downward vertical movement of air through the rotor system due to the production of lift, often referred to as downwash. When a vacuum line achieves levels of near-perfect vacuum, there is less ambient air in the vacuum lines to affect flow. The induced flow becomes more noticeable from 10” of Hg to 20” of Hg. Velocity is the hissing sound that Dental Professionals love to hear coming from their HVE and SE.
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With a better understanding of velocity and what makes a good vacuum unit, our next few segments will be diving into a deeper understanding of High-flow and Low-flow systems.