In the market for a new vac? Don’t miss these technical tips.

While there are numerous applications for vacuum excavators, including locating underground utilities, cleaning up drill fluid on horizontal directional drilling (HDD) jobs and cleaning water valve boxes, potholing is becoming one of the most popular uses for this machine. As the underground infrastructure becomes more crowded, potholing is an increasingly important step in utility projects, especially in urban areas.

“More contractors and municipalities are turning to vacuum excavators for their potholing work,” says Jeff Wage, vice president at McLaughlin. “Vacuum excavators can help crews verify the exact location of utilities, cause less ground disruption than other methods and are less likely than a shovel or excavator to damage a line.”

A simple understanding of a vacuum excavator is that it uses pressurized air or water to loosen the ground, sucks up the debris through a suction hose and deposits that material into a tank. A deeper understanding of how the components of a vacuum excavator work, though, can help contractors maximize productivity by selecting a machine that is best-suited for the projects they take on.

Read these quick facts about the following technical components before purchasing your next vacuum excavator.

Vacuum blower

  • There are two primary types of blowers in vacuum excavators: positive displacement and centrifugal units.
  • With positive displacement blowers, air enters a blower and is trapped against a cylinder until it is forced — or displaced — through a discharge pipe. This type of blower is becoming the most common for potholing due to its ability to maintain velocity and airflow when in operation.
  • A centrifugal blower typically uses rotating impellers or blades to increase the pressure or the air before discharging it.

Hose size, velocity and cfm

  • The term “cfm” stands for cubic feet per minute and is a measure of the volume of air being moved.
  • For optimal performance, the cfm specification on a vacuum excavator must be in direct correlation to the diameter of the hose on the machine.
  • Optimal hose size will depend on the type of spoil most commonly being removed.
  • Cobble, for example, will be easier to remove with a 4-inch or larger hose and will require a larger blower. Less challenging ground conditions might only require a 3-inch hose and less cfm.
  • The key is to have enough velocity so the spoils that enter the hose are suspended until they reach the tank — if the material settles in the hose, it could clog the system.


  • Inches of mercury is a unit of measurement for pressure. It is more or less a function of how much material the vacuum excavator can move, or lift, at a time.
  • For example, 15 inches of mercury is the lift involved to be able to pull a column of water 17 feet into the air.
  • The industry standard for trailer-mounted units — and for potholing and most drill fluid cleanup applications — is 15 inches of mercury.
  • More inches of mercury may be beneficial when dealing with heavy fluid or slurry.

Proper maintenance

Once you understand these technical components, proper maintenance of the equipment is the next step in maximizing productivity.

  • Changing filters as scheduled is one of the most important service tasks a vacuum excavator owner should perform.
  • Proper lubrication of the blowers is also a priority. A blower running at 15 inches of mercury can reach 300 degrees Fahrenheit, so changing the oil every 500 hours is recommended.
  • Operators should ensure that V-belts have the proper tension. If left loose, a V-belt can slip or fray and come off the machine. V-belts that are too tight can cause the blower shafts to fail.


For more information about the different vacuum excavators available, visit or contact your local Vermeer dealer.

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