Increase the effectiveness, efficiency and safety of your vacuum excavation operations.MSW Tech Talk

For a public works crew working on a congested city block, locating an existing utility is only half the battle. Locators can provide a precise target, but owners and engineering specifications will often demand visual inspection to help verify these findings. Methods such as potholing then come into play, but that still leaves the issue of dealing with the residual material after it’s removed.

More and more, municipalities 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, municipalities need to know how to right-size a vacuum excavator and follow best practices to increase productivity.

Excavator selection

Municipalities are finding new time- and labor-saving uses for vacuum excavators every day. 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.

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

Even with the numerous proven benefits of hydroexcavation, many municipalities are trending toward using air for excavation. Air excavation is typically more successful in sandy, dry or granular soils.

One of the advantages of air excavation is being able to put the soil back in the hole. 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 a vacuum excavator is just as important as the excavation method. Trailer mounted vacuum excavator selection can often be predicated on tank and blower capacity, which frequently determines hose size and overall machine productivity. Most vacuum excavators tend to feature tanks between 500 and 800 gallons; however, municipalities engaged in sewer cleaning will use truck rigs up to a 2,200-gallon capacity. For municipalities that typically work on smaller projects, smaller excavators are available with only 100- to 250-gallon capacities.

Operator best practices

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

Most manufacturers will set the water pumps on hydroexcavators below 3,000 psi, with 2,200 to 2,800 being the most popular range. Many of these machines have 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.

When working around sensitive utilities such as an aged cast iron gas line, experienced operators pay close attention to their water pressure as well as the distance between the rotary nozzle and the line to avoid damage.

Through proper maintenance and training, the potential for damage 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.

Off-loading safety

With the weight, air pressure and suction factors that come with vacuum excavator units, being aware of the safety guidelines is critical for worker safety, as well as the protection of equipment and road surfaces.

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

There is a proper way to off-load a vac unit. First, if you’re using a trailer-mounted unit, always make sure to keep it 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 unit so you reduce the tank load and weight of the tank. Finally, open the rear door and elevate the tank to dump the spoils. Some vac units come with an in-tank washout system to assist in removing spoils, while others may include a liner to assist in releasing spoils.

Many of today’s vacuum units have the ability to put a small amount of pressure inside the vacuum tank to help off-load the fluids without ever having to open the rear door. In these situations, 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.

Pressure can also help push rocks and other obstructions from the hose, but a good positive hose connection and integrity throughout the hose length is critical for this. If you’re using any kind of segmented hose, a positive cam lock style coupler is important. These couplers are ideal for positive connections when an operator is pressure off-loading or using reverse pressure in the tank to remove clogs.

Weight considerations

With trailer vacs that can weigh up to 24,000 pounds, 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 also crucial when towing vacuum excavation trailers. Having axles equally loaded and at proper hitch height is critical to the longevity of tires and 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. Either imbalance can lead to excessive tire wear or damage to either the front or back axle of a trailer.

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 an urban area has enhanced the demand and role of vacuum excavators. Before setting out into the streets, however, a municipality should compare the selection, safety and maintenance of each excavator to achieve the best possible results.

 

About The Author: Jeff Wage is vice president of McLaughlin Group.

This article originally appeared in the May 2015 issue of Municipal Sewer & Water.  For more information, please visit www.mswmag.com.

 

 

 

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