CFM vs kPa: What is most important?
Most people do not understand the difference between seal suction and velocity suction. To comprehend the two, you need to measure air intake of a vacuum suction in various ways. Lets look at seal suction and velocity suction to understand how they relate to specific uses.
First lets look at velocity suction, typically measured in cubic feet per minute (CFM or cu ft/min) or liters per minute (LPM or l/min). CFM or LPM are a measurement of the velocity at which air flows into or out of a space. CFM or LPM is a great way to measure things like blowers, fans, air purifiers, HVAC units, leaf blowers, wet/dry vacuums or suctions in general. These items frequently are designed specifically to move large amounts of air very fast. The movement of air in these units is a critical measure of the velocity of suction.
Next lets look at the seal suction which is measured in many different ways such as kiloPascals (kPa), pounds per square inch (psi), millimeters of mercury (mmHg), or millibar (mbar). Seal suction, also known as water lift suction, involves sealing a suction and connecting a tube containing water. The higher the water rises, the higher the seal or lifting suction. Seal or water lift suction (Kpa) is important in vacuums that require lifting liquids such as water over a great distance.
So, which is most important when looking at suction? It depends.
Since suctions are designed for specific uses, suctions are typically high velocity and low seal suction or high seal suction and low velocity. If you are trying to suction a large volume of air including particulates, vapors, bacteria, and viruses through a filter, you want high velocity or high CFM. If you are wanting to pull a liquid through the suction you want high seal suction or high kPa.
Many of the aerosol suction units on the market tout high kPa. These units were designed for high volume evacuation (HVE) of saliva, a viscous liquid. These units have been converted to the current market demand for aerosol suctions. You will notice that the CFM of their products are significantly lower than our aerosol suctions.
For the suction of air or aerosols, you want high velocity suction which will pull more particulate, vapors, bacteria, and viruses at higher CFM.
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Resources
https://www.greatvacs.com/pages/cubic-feet-per-minute-testing-of-vacuum-power
http://blog.bartellglobal.com/cfm-vs.-water-lift-dust-extraction-equipment
https://www.vacuumsguide.com/best-vacuum-suction-power/