Expert Vacuum Excavation

For a contractor working on a congested jobsite, locating an existing utility is only half the battle. Using a locator offers a very precise idea about where any specific utility is located, but owners and engineering specifications will often demand visual inspection to help verify these findings. Methods such as potholing then come into play, but the question becomes, “What do I do with the residual material that is removed after I’ve dug down to find the utility?”

More and more, contractors are turning to vacuum excavators to clean and remove debris created from boring projects and locating utilities. However, with the diversity in size and capability of vacuum excavators, contractors and operators need to know how to right-size a vacuum excavator and follow best practices to increase productivity.

Excavator Selection
“Vacuum excavation technology is typically used for safe and surgical digging around areas where you are sensitive to utilities and other infrastructure in the ground,” says Jeff Wage, Vice President of McLaughlin Boring Systems. “They’re also finding a bigger role in removing drilling fluid on fracking projects, pad sites, well cleanup and municipalities.”

In today’s vacuum excavator market, there are two predominant methods. Hydro-excavating uses water to excavate the hole and is particularly useful in fragmented soils or heavy clay conditions. Hydro-excavating is very useful in congested or urban areas, as it limits the amount of particulate material in the air.

Even with the numerous benefits that have been shown in hydro-excavating, many contractors are trending toward using air for excavating. Air excavation is typically more successful in sandy dry or granular soils.
“People have started to use air excavation more because you are able to put the soil back in the hole,” says Wage. “If you are using air, you don’t get the soil wet and you can put the dry material back in and don’t have to haul material in and out.”

Determining the correct size of vacuum excavator is just as important as the excavation method. Excavator selection can often be predicated on tank and blower capacity, which often determines hose size and overall machine productivity. Most vacuum excavators tend to feature tanks between 500 and 800 gal; however, contractors engaged in fluid management will use rigs up to a 1,200-gal capacity. For contractors who typically work on smaller projects, vacuum excavators can be found with only 100- to 250-gal capacities.

Operator Best Practices
The primary obligation of any vacuum excavator operator is to avoid damaging any utilities. Constant attention and adherence to training are necessary for safe and effective operation.

Most manufacturers will set the pumps below 3,000 psi, with 2,200 to 2,800 being the most popular range. However, many vacuum excavators have water pumps capable of achieving pressures up to 4,000 psi, but it is this high pressure that can lead to issues if the operator is not careful.

“Whether it is a cast iron gas main, fiber-optic line or cable TV line, any of these things can be quickly damaged with that much pressure coming out of the small tip of the rotary nozzle,” says Wage.
Through proper maintenance and using a trained operator, the potential for these damages is alleviated. The aforementioned rotary nozzle is an important piece to this puzzle; being prepared and precise are also equally important when completing an excavation project.

“The other component we emphasize is just careful digging practices. A lot of contractors will go out and re-verify utilities and depth with a locator. Often, as they get closer to the line they will dig more carefully and potentially pull back a little higher on the digging tool,” says Wage. “Additionally, they may even turn the pressure down a little bit to be sensitive to the utility as they get closer.”

Safety and Maintenance Tips
With the weight, air pressure and suction factors that come with vacuum excavator units, being aware of the safety guidelines is necessary for worker, equipment and jobsite well-being.

Safety training should begin with a focus on the suction and offloading capabilities of vacuum excavators. Hoses have positive connections for both offloading and suction, and operators need to ensure that hoses are secured properly before performing any task.

“There is a proper way to offload a vac,” says Wage. “First, always make sure to keep the vac attached to the tow vehicle. Next, open the gate valve on the bottom of the rear tank door and bleed all of the fluids out of the vac so you reduce the tank load and weight of the tank. Finally, open the rear door and elevate the tank to dump the spoils out.  Some vacs come with an in-tank washout system to assist in removing spoils, where others may install a liner to assist in having spoils slide out of the tank.”

Pressure Offloading of Fluids
Many of today’s vacs have the ability to put a small amount of pressure inside the vacuum tank to help offload the fluids from inside the vac without ever having to open the rear door. This means that a strong banded coupler is needed to help create a positive connection to the hose. Substitutions like duct tape are never recommended in place of a quality, approved coupler.

A good positive hose connection throughout the hose length is critical when using vacuum pressure to safely unclog the hose. Operators can accidentally suck obstructions into the hose. Today’s vacs have the ability to create pressure inside of the tank and push the rock or other obstruction back out of the hose and unclog it.
“A positive cam lock style coupler is important if you’ve got any segmented hose,” says Wage. “That kind of coupler is ideal for a positive connection if an operator were to use a pressure offload or use reverse pressure in the tank to remove any clogs.”

The rotary nozzle is important to monitor for safe operation and, according to Wage, it is the No. 1 wear item.
“The nozzle is in an abusive environment and too often becomes the digging tool itself,” he says. “If the nozzle becomes damaged or inoperable — losing its rotary dispersion — the high-water pressure can create risk of damaging a utility.”

Following the rotary nozzle is the suction hose. The hose can get worn down over time and often sees more rapid wear. Daily jobsite checks should also be done on the air filter going from the tank to the blower. The filter should be free-flowing and free of dust.

Cleaning the tank, vacuum float ball and full tank shutoff mechanisms should also be included in the maintenance schedule. Shutting down when the spoil tank is full reduces the risk of overfilling the tank and passing material to the final filter and blower. Finally, dumping the tank at the end of the day limits the chance of dirt and dust getting dry and solidifying inside.

Weight Considerations
With trailer vacs that can weigh up to 24,000 lbs, it is also important to perform routine maintenance on the towing and transportation equipment. Regular inspection of the brakes on a trailer hauling the excavation unit is important for both safety and fleet maintenance. Weight distribution is crucial when towing vacuum excavation trailers. Having axles equally loaded and at proper hitch height is critical to the longevity of tires, axles, as well as the trailers themselves.

“If the hitch is too high, you will put that entire load on the rear axle. If it is too low, the opposite will happen and the whole load will shift to the front,” says Wage. “Either imbalance can lead to excessive tire wear or damage to either the front or back axle of a trailer.”

A very low-rate speed should be adhered to and avoid driving over large obstacles with a fully loaded vacuum excavator whenever possible.

Excavator Importance
Vacuum excavating is growing in popularity not only out of necessity, but also viability. The ability to quickly and effectively remove dirt and debris from a jobsite has enhanced the demand and role of vacuum excavators. However, before setting out into the field, a contractor should compare the selection, safety and maintenance of each excavator to achieve a successful job.

Darrin Cline is a Features Writer for Two Rivers Marketing, based in Des Moines, Iowa.