Choosing the Right Vac Truck for Your Application

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Choosing the Right Vac Truck for Your Application

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With the miles upon miles of subsurface utilities being installed, repaired or replaced every day, the methods by which contractors unearth underground utilities are always evolving. Soft digging using hydro or air excavation units to safely locate and daylight underground utilities has grown in popularity due to its safety and accuracy. As the market for these machines continues to grow with more manufacturers and models available, proper education is vital to choosing the right machine for your specific application.

How it works

Hydroexcavators use high-pressure water (air excavators use compressed air) to penetrate through dirt, while the unit’s vacuum system is used to remove loose ground contents in a process referred to as potholing. This soft excavation method can quickly expose underground utilities without damaging any conduits, pipes or lines in the process. When choosing the right truck, there are many factors to consider.

Vacuum blower

One of the first components to consider is the vacuum blower. Essentially, the vacuum blower creates the suction required to actually lift the debris out of the ground. When it comes to blowers, there are two types commonly associated with vacuum excavation: positive-displacement blowers and fan units.

With a positive-displacement blower, air enters the blower and is trapped within a cylinder until it is displaced through a discharge pipe. This blower type is a favored option for potholing since it maintains consistent velocity and airflow while in use, making it reliable regardless of application.

A fan blower typically uses rotating impellers or blades to increase the pressure or the air before discharging it. These units are less popular, because while they are capable of higher air flow, any change in pressure can drastically lessen overall air flow.

One of the metrics used to gauge air displacement is cfm, which stands for cubic feet per minute and is a measure of the volume of air being moved. The hose size required for each application is directly related to cfm. The larger the diameter of the hose, the more cfm is required in order to maintain suction. There should be enough strength so that all the debris makes it to the holding tank, and none of it falls and collects in the suction hose.

Larger, denser material will likely require a 6- or 8-inch system to keep the vacuum hose clear of debris. Lighter material, like dry sand or loose dirt would lend itself to an air application with a 4-inch system.


Inches of mercury (Hg) determines hydroexcavation vacuum pressure. Inches of mercury determines how much material can be lifted at once and how high into the vacuum tube the material can be pulled.

For example, 18 Hg is the lift involved to be able to pull a solid column of water 20 feet. More inches of mercury may be beneficial when dealing with heavy fluid or slurry, as this pressure allows more volume of material to be displaced before air induction would be required to maintain proper velocity and suction. Standard hydroexcavation units provide 18 Hg, but can be upgraded to 27 Hg, depending on the application and material being vacuumed.

What brand is right for you?

With a number of truck manufacturers in the hydro and air excavation market, the amount of vacuum power a truck delivers is very important, but there are other features worth considering, such as available water heaters, boom reach, directional discharge system, debris tank size, water system enclosures, safety, ease of operation, etc. Buyers should ask sales representatives questions regarding operation to ensure the unit will meet their application.

It is also important to consider the quality of support that can be expected after the sale when choosing a reliable equipment dealer. Whether selecting a truck as a rental or for direct purchase, Rock Rental offers a large variety of new and pre-owned equipment available for immediate delivery. Rock Rental works with nationally recognized financial institutions to assist you in obtaining the financing you need to get you into the equipment your business requires. Contact 833-482-7625 for more information or email


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