Optimal Operation

While air and water vacuum excavation systems apply state-of-the-art technologies to safely and efficiently expose underground utilities, their overall success on the job are dependent upon skilled operators following important guidelines. These include safe and proper operating practices, as well as an effective maintenance regimen.

Safety First
Trevor Connolly, vice president of sales and marketing at Vacmasters, a leading air vacuum excavation equipment manufacturer, says the most important operational tips are those regarding safety.
“Personal protective equipment (PPE) is always necessary when operating air vacuum excavating systems, including eye guards, ear guards, gloves, appropriate work wear and hard hats. In any excavation, shooting water or air into the ground can dislodge small rocks and pebbles that can fly out before the vacuum hose catches them. Protection is important.”

When beginning a hole with an air excavation system, Connolly recommends using some type of barrier or digging shield to help avoid rocks and other debris that can fly out. Digging shields are steel cones or cylinders used on the ground over the hole. The system’s air lance goes in through the top, the vacuum hose goes in through the side and the sides act as a barrier. The shield contains all of the potential flying debris, allowing the vacuum hose time to catch it. Once the operator reaches 6 to 7 in. in depth, the shield should be removed, since it limits visibility for further digging.       

Connolly says another important operational note is to use a “stirring-the-pot” motion and not a jabbing motion like putting a stake into the ground. He says, “There is a steel tip on the end of the air lance, and you could potentially jab it into a utility if you’re not sure of its location.”

Tweaking Your Technique
When it comes to operating vacuum excavation equipment, technique is key to productivity. Ben Schmitt, product manager at Vactor Mfg., a leading manufacturer of sewer and catch basin cleaners for more than 45 years, explains the two most common techniques used with water excavation systems. While soil conditions play a role in selecting the most productive method of vacuum excavation, each method has its advantages and disadvantages.

One method uses low-flow water along with surgical cutting. This method conserves water, allowing for longer operating time without refilling the water tank and less water in the debris hopper to haul away and dispose.

Another method uses a high-flow spray to quickly erode the soil and wash it down to a vacuum point. While this method is productive in terms of time on the job, it requires significantly more water, and a higher percentage of the load is water, not excavated soil.

During real-world operation, Schmitt says equipment set-up is important. “All too often, vacuum excavation customers believe the fastest method is simply to turn every setting to its maximum but this is usually counterproductive,” he says. “The right amount of water and the right amount of vacuum leads to the highest productivity and increased unit up-time. Over-working the equipment when the application doesn’t call for it leads to increased wear and tear on the vacuum system and chassis. Selecting the right mix of power and performance will complete the job in the same amount of time with less wear on the equipment.”

Clearing Clogs
All vacuum excavation equipment, regardless of its hose diameter, can experience obstacles such as rocks and other pieces of debris lodging in the hose. These bits and pieces can significantly slow the air flow down and bind to other clumps of dirt in the hose — leading to a full-blown clog.

How often clogs occur depends on the type of soil that’s encountered. For example, stickier clay soils can bind easily to the sides of hoses making clogs likely. However, with appropriate techniques, operators can minimize them so they don’t affect daily progress.

“When clogs happen, try to pinpoint where they are and break them loose,” says Connolly. “Strike the hose itself or vacuum up a very small amount of water to lubricate the inside and dislodge it. But, it’s important to not cause clogs in the first place.”

Connolly points out that proper operational technique can go a long way in preventing clogs, such as instructing operators not to simply submerge the hose into the hole. “Because of positive displacement, the blower needs a constant flow of air running through it,” he says. “If you simply insert the hose down into the dirt, you don’t allow air to go through it. We recommend the operator moves the hose up and down to allow air to transfer at a minimum conveying velocity that allows successfully vacuuming of the material. Cutting off the air supply drops the minimum velocity, so material binds to the side of the vacuum hose. It’s important to introduce a constant stream of air.”

In addition, Connolly suggests:
• Use the proper vacuum hose for the soil conditions. Plastic hoses are most effective in sticky, wet, clay soils, and rubber hoses are best suited for sandy, abrasive soils.
• Avoid vacuuming too rapidly which can overload the hose with soil.
• Try and avoid curves in the hose and keep it as straight and short as possible.
• If hose clogging remains a problem, a Barrel-Top Interceptor option limits the hose clogging to a very short section of easily cleaned hose.

Effective Maintenance
As with any piece of machinery, maintenance is critical to keeping a vacuum excavator functioning. Vacuum excavators are powerful machines, so keeping them in top working order will lead to longer life, higher levels of productivity and better retained value.

Maintenance items vary from daily checks of hoses, drain points and oil levels, to semi-annual probe, sensor and bolt inspections. Each manufacturer will provide a comprehensive list of recommended scheduled maintenance.

“It’s critical to check safety-related equipment on a daily basis prior to use, such as guards and vacuum protection devices,” says Schmitt. “Also, inspect oil levels, vacuum hoses, water hoses and fittings on a daily basis.”

Vacuum excavators rely on hydraulics to power moving parts, so a clean and well-maintained hydraulic system is essential to keep the equipment operating. Grease each moving joint periodically to prevent binding.

Wear items — such as vacuum hoses and tubes — require frequent inspection due to the highly abrasive nature of vacuum excavation. Schmitt says to also check and maintain the air filtration system to protect the vacuum system and prolong the life of the components.

In addition to the maintenance required on vacuum excavators, hydro excavators require a little extra TLC on their water pump systems. This includes inspecting, cleaning and replacing filters to protect foreign matter from entering and damaging pump seals. Not to mention, the handguns and water lances should be inspected to ensure they are in safe working order.

Debbie Sniderman is an engineer, consultant, writer and CEP of VI Ventures LLC.