Air vs. Hydro

In the end, it’s a matter of personal preference; each method has its place at certain job sites.
Air vs. Hydro
Davids Hydro Vac in White Bear Lake, Minnesota, disposes of slurry after hydroexcavating at a job site near the company’s yard. Davids Hydro Vac prefers to use hydroexcavation because of the cold ground conditions crews face in the winter.

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The rivalry of air and water goes waaaay back. Classic Greek thinkers were fascinated by the impact of these two elements on a third element of nature, earth. Today, excavation companies are still fascinated, and increasingly leverage air and/or water in their earth-digging operations.

So, air or water — which is the better option than a hydraulic excavator? The classic response is, that depends.

“Air has a place,” says Mike Morehouse, CEO of Davids Hydro Vac in White Bear Lake, Minnesota. “Hydro does, too. Each also has its limitations.” Morehouse uses both, though the preponderance of his excavation work is with water. “The key is to use what will work best. We leave it up to the operators. They are the ones who have to get the job done.”

Morehouse and his operators use the air-vac system just 5 percent of the time. “Hydroexcavation is faster. There’s no doubt about it,” he says, and alludes to his own learning experience with the two systems. “I didn’t know what I was doing at first, but I eventually figured out that if I used air and water, I was moving more material.”

Of course, it all depends.


The two systems employ forceful injections of air or water to cut into the earth, and it’s not uncommon for both systems to be mounted on a truck for switching from one to the other during an excavation. An air system is pressurized by a compressor unit that can generate kinetic force through high-pressure hose at a rate of 350 cubic feet per minute at 250 pounds per square inch. Water is injected through other hoses at a rate of 5-15 gpm at 3,000-4,000 psi, though lower pressure is generally used.

Both systems employ vacuum pumps that suck up the dry or wet excavated material at a rate of 1,000 cfm or more. The material is deposited in tanks that can hold the equivalent of 300-1,000 gallons of dirt or slurry. Each tank features a wide-opening end door for dumping the accumulation.

Which system completes an excavation faster and most cost-effectively can depend on how far away a hydrovac truck must travel to dump a full tank, and how much time and expense is involved in trucking in replacement soil.

“The main thing is an air-vac system doesn’t have to get rid of spoil and doesn’t have to import any soil,” says John West, vice president of Ultra Engineering of Winchester, California.

“We can do an entire hole in half an hour from opening to backfill. If you are using water, you won’t get it done that quick. And at the end of the day, we don’t have any spoil to dispose of, which saves time and money.”

Says West: “Water has its place, but out here in California, air is taking over.”


Ken Baker has a different view. His viewpoint is the Mountain West — Wyoming, Colorado and Utah — where clay soils are common, and cold along with record snows this year made the ground even harder to penetrate. “Out of the whole year, we can have four, five, six months of frozen ground where we have to use a boiler to heat up the water. Air has limited impact in those conditions.”

Baker, who is president of Baker Hydro-Excavating of Mountain View, Wyoming, says he, like the ancient Greeks, keeps going back to the elements. “You consider air versus water in nature. Which erodes earth faster? Water.” So Baker’s 400 hp Kenworth trucks exclusively carry hydroexcavation systems.

Does he sometimes wish he had an air-vac unit on board? “No. The only thing I would say is that if we ended up going back for more excavation at a site, I could use air in that situation because the ground already would be broken up. That would be a little bit faster and wouldn’t cause the mess created with water. Not having to dump is one advantage air-vacs have.”

West is more flexible. He believes water is a good option to have on hand for his Ultra Engineering air-vac projects. “We never absolutely have to use water, but sometimes we use it to soften up the dirt a little. We never dig an entire hole with water, but we sometimes do dig a pilot hole.”


Across the country, potholing accounts for most air-vac and hydrovac work, 75 percent in the case of Ultra Engineering. At a local airport, his crew once potholed down 35 feet to confirm the presence of a gas line. But trenching is common, too. “At Disneyland, we do a tremendous lot of trenching,” West says. “They don’t want anything to happen to the roots of the trees in the park.”  

Air or hydroexcavation projects vary widely. Baker once excavated a trench 10 feet deep and only 1 foot wide. He also had five trucks simultaneously dig a large pit 25 feet deep. Other typical applications include digging of elevator shafts, cleaning and vacuuming of fracking tanks, clearing out debris from beneath cattle guards, and tunneling underneath utility lines.

And West reports that, with rain finally returning to California, “a lot of construction contractors hire us to clean up their footings. That happens when a contractor is ready to pour and rain falls overnight, and the next morning mud covers the rebar. We air-vac it up. You can’t do that with a hydro system.”  

All in all, Morehouse calls air-vac and hydro-vac excavation “a great, flourishing industry.” He personally is working to help it expand further: visiting trade shows and manufacturers, networking, and exploring how other industries might enhance the air-hydroexcavation business. “I’m finding stuff.”


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