Industrial vacuum systems have been part of municipal fleets for decades, used for a host of tasks from cleaning sewers, catch basins and water valve boxes, to removing slurry from horizontal directional drilling projects.
Truck-mounted combination units offer high-pressure waterjets for cleaning and powerful vacuum for picking up debris. Besides cleaning chores, they can be easily adapted for hydroexcavation, which enables digging safely around buried utilities and exposing those utilities for repair work.
Because these machines are versatile and highly efficient, municipalities and contractors who buy one often find it fully utilized within a short time. Faced with a large expenditure for a second truck-mounted unit, many instead choose a trailer-mounted system. This lets them keep the truck unit free for major projects that require maximum power and use the trailer unit for the small- to medium-sized jobs.
Small package
A wide array of attachments can make combination units even more versatile. For example, reduction tools in different sizes allow cleaning of smaller valve boxes and basins. A valve exerciser attachment, which mounts to the vacuum trailer, can save crews the manual labor of hand cranking valves.
Sometimes ground conditions or confined spaces make a work site unsuitable for a truck vacuum. Here, a more mobile trailer vacuum can provide easy access.
An expanding application for combination units is for excavating post holes for road guard rails and traffic signs. Hydroexcavating prevents damage to buried utilities and requires less labor than using an auger.
Trailer-mounted vacuum excavators are well suited for these applications because they are portable. A city or utility can choose anything from a 100-gallon unit that fits in the bed of a 1-ton truck to a full-size trailer unit with up to a 1,200-gallon capacity. The larger units have the power to move displaced soil up to 200 feet from the source, yet require only one person to operate.
Trailer-mounted vacuums have some limitations. Most trailer units deliver vacuum capacity of about 15 inches Hg, providing a solid water lift of 15 feet from the port without introducing air into the stream. It is possible to go 30 or 40 feet deep if some air is mixed with the material being vacuumed.
Large vacuum trucks typically deliver at least 20 inches Hg and so can lift a column of water from a greater depth without introducing air.
In addition, the positive displacement blowers on trailer-mounted systems are typically smaller, providing 575 to 1,025 cfm air flow, compared to 3,000 cfm and up from some larger truck units. Smaller units use only 3- or 4-inch hoses, compared to the 6-inch hoses found on truck models. The smaller hoses provide less suction, but do allow access to tighter spaces.
Making sound decisions
In choosing a trailer-mounted combination machine or vacuum excavator, contractors should look at a variety of factors that affect proper sizing and the selection of equipment and accessories. Major considerations include:
What is the main application? Will the unit be used for jetting small sewers and cleaning of valve boxes and catch basins? Heavy-duty sewer cleaning? Potholing? Major hydroexcavation projects?
What options are desirable? Is there a need for a valve exerciser? Sewer jetter? Reduction tools? Heater for excavating in heavy clay soil or in frozen conditions?
Is there a need for dry as well as wet excavation? Water-based excavators typically dig faster through a wide variety of soil types and reduce the volume of the displaced material. They also move more displaced wet spoil to the 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 both systems in one package, letting the user choose the best option for the job.
The heart of the system
In comparing machines, users should look for a high-quality vacuum blower. They should also select a tank with capacity to hold a half-day’s or day’s worth of spoil, as this reduces the number of trips needed to empty the debris tank.
If a hydroexcavator will be used in areas with cobble rock, then a unit with a 4-inch hose and a blower with about 1,025 cfm air flow is desirable. Cobble soils require a larger blower to remove spoil effectively, and the larger hose helps limit clogging.
In areas without cobble rocks, a 575-cfm system and 3-inch hose will generally suffice. Blower size affects the amount of engine power required: A larger blower increases the cost of the unit.
Communities should select a filtration system that filters the spoil without clogging. Also important is a strong trailer frame that will support the weight of the unit and a full tank of spoil over a long equipment service life. Options on trailer units can include:
• Controls that allow the user to reverse the flow of the vacuum to blow the spoil back into the hole.
• Booms that support the weight of the hose, reducing operator effort.
• Automatic tank clean-out systems.
• Auxiliary hydraulic systems that allow users to run a concrete saw and other tools off the unit.
Trailer vacuums are a great complement to a truck vacuum and a versatile tool for busy municipal crews and the contractors who serve them.
Mike Moore is vice president of sales with McLaughlin, a manufacturer of vacuum excavation and auger boring equipment and underground locator technology in Greenville, S.C. He can be reached at 864/277-5870 or mmoore@mightymole.com.
