Suck It Up
Putting Vacuum Excavators to Work on Utility Jobsites
By Jason Morgan
 When someone says “excavation,” the first machine that comes to mind might be an excavator or backhoe loader. Or maybe hand digging around sensitive utilities. But there’s more than one way to dig a hole. Vacuum excavation is a minimally invasive excavation method that offers advantages for contractors who dig around buried utilities.
Vacuum excavators are self-contained units that use pressurized air or water to displace soil and create dry or wet spoil. The displaced dry or wet spoil is removed from the area through a hose using high-velocity suction and stored in a holding tank on the vacuum. Vacuum excavators can be mounted to a trailer or the back of a truck and range in size from 100 to 1,200 gal of capacity.
“Since vacuum excavators use low-pressure air or water to remove spoil, they are perfect for potholing to identify existing utilities during underground construction projects,” says Mike Moore, Vice President of McLaughlin, a manufacturer of vacuum excavators, boring systems and utility locating solutions. “In fact, the air and water move around the existing utilities, giving the operator a clear view. Operators can select the amount of air or water pressure depending on the utility. A lower pressure of 1,500 psi should be used for gas and fiber lines in order to not damage the line coating. A higher pressure can be used for water lines.”
As Moore alluded to, there are two basic types of vacuum excavators — water and air. A hydro-excavator uses a concentrated jet of highly pressurized water to excavate and an air excavator uses a concentrated jet of highly pressurized air to excavate. The vacuum is used to clear excavated material from the hole for visibility and access. Depending on the nature of the excavation, material vacuumed into the tank may be used for backfilling the site or off-loading into a separate container or site.
“Either pressurized air or water can be used effectively for excavating,” says Jared Dippel, Product Manager, Vactor Mfg. “Excavating with air produces a drier payload, which allows immediate use of excavated material as backfill. Excavating with water produces slurry, which can be difficult to use as backfill.”
Air provides an infinite digging medium. With water, you’re limited by the truck’s tank capacity. For utility applications, the air compressor on an air unit can be used to run various tools such as saws and jackhammers. Hydro units can be equipped with an add-on air compressor. Water — especially heated water — at certain pressures will cut better in frozen ground and clay; whereas air has limited effectiveness in these conditions, explains Dippel.
Water is an effective method for digging in a wide variety of soil types. It’s quicker than air in reducing the soil, but the downside is that you’re left with spoil that’s muddy. Air, on the other hand, is not as fast, but is neater. You’ve got dry material to put back into the hole, but dense soil tends to give air more problems.
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| Operators need to understand and avoid the potential dangers that can be associated with working with highly-pressurized air or water. Likewise, if operators are working with units that use heated water, they should be aware of and avoid coming in contact with hot surfaces or hot water. |
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The primary use of using vacuum excavation on a utility site is unearthing utilities. Water can be dialed into pressures that will not harm underground utilities, but will still be effective separating the soil particles and carrying them into the vacuum.
Air is compressible, so if it hits something hard, it will compress and flow around it, avoiding any damage. But there are a myriad of applications beyond carefully unearthing utilities.
Contractors are finding new uses for vacuum excavators that save time and labor. A wide array of attachments can expand their applications.
Different size-reduction tools allow cleaning of smaller water valve boxes and catch basins. A valve exerciser attachment, which mounts to the vacuum trailer, can save crews countless hours of exercising valves from one stationary location, eliminating the old-fashioned hand cranking method.
“Some contractors are even using these units to remove grain and coals trapped in the corners of barges, clean gutters and remove the chips from stump removal projects,” says Dippel. “An expanding application for vacuum excavators is their use to excavate post holes for road guard rails and traffic signs, as well as small excavation projects. If you need a larger hole, you can repeat the process in spots. Using a vacuum helps eliminate the chance of damaging an existing underground line and requires less labor and time than using an auger.”
To accomplish these wildly varied tasks, vacuum excavators can be configured in a multitude of ways. While attachments like augers and valve exercisers extended the vacuum ex’s applications, nearly every component of the system is customizable — from the spoils tank to the vacuum power.
“You can set larger [hydro excavators] up to be a mud cleanup for an HDD system and smaller capacity vacuums for cleaning and exercising valves,” says Richard Levings, Ditch Witch Senior Project Manager. “If you’re going to do lots of hydro excavation, you can have larger volume tanks, higher pressure systems for higher vacuum capabilities. It depends on if you need to have a large number of potholes in a day’s time? You’re probably going to go more powerful. If you don’t have that many and have a lower tow vehicle, you’ll go with the smaller setups.”
Vactor makes sure to distinguish if the application calls for fan or positive displacement (PD) units. A PD blower is used in applications that involve excavating over long distances and at excessive depths. PD units are more powerful but slower than fan units.
PD is ideal for oil field work or large excavations. Fan air conveyance is preferred for applications where speed is a factor.
These units are easy to operate and maintain. They also have lower noise levels and add less overall weight to the unit.
It’s also important to pay attention to the filtration system — both before the purchase and afterward during maintenance checks. “With air, you need better filtration to overcome the tendency of dry material particles that get caught up in the stream and carry over to the vacuum source. In hydro applications, material typically settles out more completely and has less chance for carryover,” says Dippel.
If you’re torn between deciding between two systems, a new breed of vacuum ex has ben spotted on jobsites.
In the past year, manufacturers, including McLaughlin, have offered machines that provide both hydro and air solutions in one machine. This provides an additional level of flexibility and ensures that the contractor would be able to tackle any task, regardless of soil condition.
“McLaughlin uses a three-stage filtration system that allows for both wet and dry vacuum excavation,” says Moore. “First, material enters the tank at 130 mph and the large soil particles lose velocity and fall out of the filtration system. Next, the air moves to a pre-filter cyclone where the remaining small particles drop into a collection tank. Finally, the pre-filtered air enters a washable micron-poly filter that traps the remaining fine particles.”
Because of the vast customization vacuum systems offer, prices for a basic unit can start around $70,000 and sky-rocket upwards of $400,000 for large truck-mounted systems with 12-yd capacities. Another example would be a 6-yd truck, which can range from $180,000 to $250,000, depending on the options. That’s is no small chunk of change in a tight economy.
“Customers generally have become more price-conscious, sometimes leaning toward smaller units,” says Dippel. “On the other hand, at Vactor, we’ve seen an increase in demand for combination units despite their somewhat higher price point because people are interested in the versatility and ability to get more use out of the machines.”
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| When unearthing utility lines, water can be dialed in to pressures that will not harm underground utilities. Air is compressible, so if it hits something hard, it will compress and flow around it, avoiding any damage. |
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If you’re new to vacuum excavation, the wizardry of sucking up earth with no conventional digging apparatus to wield might seem counter-intuitive. But have no fear, your local dealer can handle all the training you’ll need to hit the jobsite running.
“That’s where our local dealers offer added value — in service and operational training,” says Levings. “They often know where vacuum excavation is most effective and where there is work to help provide direction. They also take care of the parts and repairs.”
Operators need to understand and avoid the potential dangers that can be associated with working with highly pressurized air or water. Likewise, if operators are working with units that use heated water, they should be aware of and avoid coming in contact with hot surfaces or hot water. Eye and face protection should always be worn to guard against injury from the debris that can be expelled through the excavation process.
Additionally, operators must be aware of their surroundings — whether they are power lines above or gas in the ground.
When you’re aware of the hazards, you can determine the best ways to work around them and complete the job safely.
If you’re using a hydro vacuum excavation, some job specifications might have you dealing with contaminated soils.
In these cases, it’s important to check your local legislation for the proper way to handle hazardous materials.
“Depending on the municipality and location, many times the municipality will designate an area where you can dump,” explains Levings. “If you’re going to clean up a site somewhere, you need to know the state’s regulations for as hazardous materials, where you have to dump it and that you are qualified to be on that type of jobsite. You need to be properly certified to handle that material.”
Beyond that, if you have a problem you can always contact your dealer or consult the operator’s manual. As long as you know what you’re digging in and the One Calls are done, you’re in good shape to start potholing the jobsite, cleaning up trench boxes and any other application you think your vacuum excavator can handle — the ground’s the limit.
Jason Morgan is Associate Editor of Utility Contractor.
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