Portable vacuum excavators have been a regular sight on jobsites for years. These unique units were originally used to clean septic tanks and car wash pits and to remove slurry from horizontal directional drilling projects. Now contractors are discovering that these machines have a wide range of uses on the jobsite, from potholing for utilities to cleaning valve boxes to digging post holes.
"The vacuum excavator has come of age," says Dave Gasmovic, president and CEO of McLaughlin. "Contractors are discovering that vacuum excavators have multiple uses to help reduce labor costs and speed up projects."
Vacuum excavators are self-contained units that use pressurized air or water to displace spoil and a pump to remove the displaced spoil. The displaced dry or wet spoil is 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 1200 gallons (379 to 4542 L) of capacity.
Since vacuum excavators use low-pressure air or water to remove spoil, they are perfect for potholing or identifying existing utilities during underground construction projects.
"Damaging existing utilities can be costly in terms of project downtime and potential contractor fines," says Gasmovic. "The low pressure water and air will not damage existing utilities like a backhoe, compact excavator or shovel. 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 should be used for gas and fiber lines in order to not damage the line coating, while a higher pressure can be used for water lines.
Contractors are finding new uses for vacuum excavators every day 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. 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. Gasmovic says he’s seen holes of up to 4 square feet dug in this way. Using a vacuum helps eliminate the chance of damaging an existing underground line and requires less labor and time than using an auger.
According to Gasmovic, today’s trailer-mounted vacuum excavators are well-suited for these applications because they are more portable than older units. Contractors can choose a 100-gallon unit that fits into the bed of a 1-ton truck or trailer units of up to 1200 gallons. These units also have the power to move displaced soil up to 200 feet from the source and only one person is required to operate the unit.
"What we find is that when a contractor or municipality buys their first vacuum, everybody starts coming up with different ways to use it," says Dave Gasmovic, president of McLaughlin. "It might have been bought to just clean out water valve boxes, but soon the sewer department’s borrowing it to clean out catch basins and the electric department is borrowing it to expose electric lines."
Selecting the Right Unit
Vacuum excavators come in all sizes and options, so it’s important to select a unit that will best fit your intended use. Water-based units typically dig faster than air-based units through a wide variety of spoil types and reduce the volume of the material, meaning you can get more displaced wet spoil into a holding tank than with an air system. However, the displaced spoil is wet and cannot be returned to the site immediately without drying.
On the other hand, spoil from air systems can be directly returned to the site, but these systems do not cut as well in hard ground conditions, such as clay.
If you are working in areas with cobble rock, then a unit with a 4-inch hose and 1025-cfm blower unit will be more productive. Cobble soils will require a larger blower to effectively remove the spoil. The larger-diameter hose will help reduce the potential for clogging. In areas without rocks, a 575-cfm system and 3-inch hose will suffice. The blower size also affects the amount of engine power required: A larger blower will increase the cost of the unit.
"I encourage contractors to look for a unit with a good-quality vacuum pump, the heart of the vacuum," say Gasmovic. "They should also select a tank that has the capacity to hold one-half day’s worth of spoil. This will reduce the number of trips you need to make to dump the holding tank."
Gasmovic also encourages contractors to pay special attention to the filtration system and select a system that will filter the spoil and avoid clogging. Finally, be sure to select a strong trailer frame that will support the weight of the unit and a full tank of spoil.
Gasmovic recommends that contractors consider the following before purchasing a vacuum excavator:
- What is the main application? The contractor should consider whether they plan to use the unit for jetting small sewers, potholing for utilities, or cleaning valve boxes and catch basins. This will help determine the scope of uses for the unit.
- What options do they want on it? Depending on the application, the contractor may need to consider purchasing a valve exerciser, sewer jetter or various reduction tools to match the type of utilities and soil types when potholing.
- Do they need dry as well as wet excavation? Water-based units typically dig faster through a wide variety of spoil types and reduce the volume of the displaced material. These units move more displaced wet spoil into a holding tank than an air system. However, the displaced spoil is wet and cannot be returned to the site immediately without drying. While spoil from air systems can be directly returned to the site, these systems do not cut as well in hard ground conditions, such as clay. Some manufacturers offer the advantages of both systems in one package, which allows the user to decide if wet or dry excavation is best, based on the project at hand.
There are number of options available: controls that allow the contractor to reverse the flow of the vacuum to blow the spoil back into the hole; booms that support the weight of the hose, placing less effort on the operator; combo units that include a jetter to clean sewers and remove the resulting trash; automatic tank clean-out systems and auxiliary hydraulic systems that allow the contractor to run a concrete saw or breaker off of the unit.
When you have a vacuum excavator, the number of uses will just multiply with a little creativity, adds Gasmovic.
Greg Ehm is a Technical Writer with Two Rivers Marketing, Des Moines, IA