What is the difference between Suction Lift and CFM?
First, let’s define each term. CFM or Cubic Feet per Minute is the measure of air flowing through a vacuum system. CFM is the the speed of the air flow. CFM equates to a car’s top speed. Suction Lift is the measurement of the vacuum’s ultimate power. This can be compares to a car’s horsepower. It’s measured in inches of Mercury (Hg) or water. Mercury is 14 times heavier than water, so to convert inches of water to inches of Hg, just divide inches of water by 14.
A pump is constantly trying to create a vacuum. When you place a hose in a sump with the open hose end submerged, the CFM or vacuum air flow will decrease and the suction lift will increase. A vacuum is created pulling the sump contents into the hose. It is the suction lift, not CFM, that creates the suction for lifting solids and fluid out of the sump. The more suction lift, the faster weighty solids can be picked up. If you can’t lift the heavy stuff, your vacuum will be of limited help with the tough sump cleaning jobs.
When the open hose end is not submerged, suction lift will decrease and vacuum flow will increase. The speed of the vacuum flow will allow for faster recovery when suction lift is lost and increase nozzle velocity to help pick up dry metal chips or very shallow puddles. Depending on your application, you may look for a balance between CFM and suction lift. Most shop size, high CFM units must sacrifice suction lift to produce that high CFM. This will hamper your ability to effectively clean a sump. At CECOR, we have some units that have good CFM without sacrificing suction lift. Call us 1-800-356-9042 to discuss your application.