Vacuum excavating is a process of using water or air to dig around the existing utilities in order to expose them without damage. Since cables and pipes began being installed underground, the laws have become more restrictive about how a contractor can drill around them.

President of McLaughlin Group Dave Gasmovic said “The problem was getting to this stuff in a nondestructive fashion. In fibre-optic cable, a shovel can cut just as easily as a backhoe. There had to be a better way to expose utilities.”

Using a vacuum excavator as a damage prevention tool makes sense said Mr Gasmovic. “There are other damage prevention uses as well. You may have to dig around signal bases on traffic lights, or clean up loose asphalt after cutting to raise manholes.” An important consideration is the machine’s cubic feet of air permitted and whether working with air or water.

“Water is a more effective method for digging and will allow digging in more different types of soil,” said Mr Gasmovic. “It’s quicker than air in reducing the soil; the vacuum removes it, but the downside is that you’re left with a tank that’s muddy.” Air is not as quick, but it is neater. “You’ve got dry material to put back into the hole, but not every soil works well with air. Some of the new vacuums in the industry use a combination of air and water.” Uses for vacuum excavators

Vermeer underground segment Manager Ed Savage said “Anytime you drill, you’re going to produce mud. The mud has to be cleaned up and vacuum excavators are a very efficient method. Another use is cleaning our valve boxes.”

Vacuum excavators can be thought of as one big wet-dry vacuum. “Almost anywhere you remove a dry or liquid no hazardous material is a great place for a vacuum excavator,” said Mr Savage. In North America customers have used vacuum excavators to suck up spoiled grain in Iowa as well as clean out animal pens at a zoo in Mexico. “We even had a place in Florida that used a sickle mower to mow around a lake and cut off all the lily pads and loose materials, and then sucked them up in the vacuum.”

Because of the difficulties of transporting hazardous materials, vacuum excavators are not recommended for cleaning up oil spills or other hazardous materials. How potholing works

Potholing – the process of digging a hole to locate utilities – can be a disaster if utility lines are cut through or a mess is created. Mr Savage especially recommends a vacuum excavator when working on front gardens, to minimise the damage caused by potholing.

Having the vacuum excavator perform at the correct speed is important. Mr Gasmovic said “About 130 miles per hour is the correct air velocity to move a material that has mud, dirt and gravel in it. What you do is have a method to apply the water to the ground. A reduction tool with four nozzles on it is recommended, with a water system of 3,000 - 4,000 psi.

If using the special reduction tool, it is recommended that the psi is reduced to a safe level where damage to the cable is unlikely.

The reduction tool is placed over the spot to be excavated, and the water trigger is keyed, which starts the flow of water into the reduction tool. The soil that is being loosened is vacuumed up along the way. The process is continued until the utility is hit, when the operator will start feeling resistance from the tool.

A reduction tool that has two nozzles can cross-cut the soil. The procedure leaves about a 6 inch hole, when it gets to a cable or pipe, the water exposes not only the top, but the entire cable. The vacuum pulls out all the water and mud, leaving a clean, dry hole. If a larger hole is needed, the process can be repeated in spots, holes of up to four feet square have been dug in this way.

Soil considerations

Clay soil is difficult, but not impossible. Mr Savage said “Just like any other piece of trenching equipment, soil conditions make all the difference. Some soils simply work better than others.”

Clay soils do not work well with air systems. “In vacuuming in general, there’s a standard type system that uses a 3 inch hose and maintains 130 miles per hour,” said Mr Gasmovic. “If you use a 575 cfm blower, and in some cases have rockier soil, you need a bigger hose – I’ve seen people go to a 4 inch hose and 1,025 cfm to maintain that air velocity.”

Mr Savage said another option is adding detergent and polymers to clay soil to keep it from sticking, “once water hits it, clay gets really sticky and hard to handle.”

Potholing myths

Mr Gasmovic said that when considering a vacuum system, most people think that the larger the vacuum the better – in his opinion, this is not true. “Normally you run with about 15 inches of mercury. Bigger might be better if you’re trying to lift a full column of water. In excavation, you’re not lifting a solid column, so the secret is velocity, not inches of mercury.”

Another feature that potential buyers often look at is the way the machine is made for emptying and cleaning. “Most small vacuum excavator systems use a bag house, and that makes emptying messy – there’s mud on the bag and moisture in there. If the bag gets damaged, it can be expensive,” he said.

Alternatively, machines that use a filtration system eliminate the need for a bag house and enable the machine to operate more efficiently, this way it can operate wet or dry. Vacuums with a bag house cannot vacuum dry. Vacuums without a bag house are also less expensive to maintain, due to an inexpensive washable filter said Mr Gasmovic.

The way this system works is that as the material comes into the tank at 130 mph, it hits the tank and the velocity drops to zero. Most of the big materials fall into the tank, just like every other system being manufactured today.

With a filtration system, air flow goes into a separator that starts the air spinning. As the air spins, the smaller particles get thrown to the side of the canister and drop out into a small collection tank, which acts as a pre-filter.

Once the material comes through a separator, it goes through a final washable filter and returns to the blower and is recycled again.

Sizes for all needs

Vacuum excavators are now available in sizes ranging from a 100-gallon unit that fits in the back of a ute to 1,200-gallon units. “Many of our customers appreciate the smaller units. It’s a smaller footprint machine and more economical than a big vacuum truck,” said Mr Gasmovic.

This product is suitable for anyone doing any kind of digging. “Whether they’re underground utility contractors, municipalities or anyone who needs to expose utilities to trench, plough or do directional drilling, the vacuum excavator is the way to go,” said Mr Savage.