Periods of rain. Low near 55F. Winds light and variable. Chance of rain 100%. Rainfall near a quarter of an inch..

Periods of rain. Low near 55F. Winds light and variable. Chance of rain 100%. Rainfall near a quarter of an inch.

Street sweepers don’t use vacuums to pick up crud from roads. Instead, the backward-spinning main broom flings the gunk onto a conveyor that leads to a hopper — as shown in this diagram of Mankato’s newest street sweeper.

Street sweepers don’t use vacuums to pick up crud from roads. Instead, the backward-spinning main broom flings the gunk onto a conveyor that leads to a hopper — as shown in this diagram of Mankato’s newest street sweeper.

Street sweepers are out in force this time of year. I was wondering how they work — it looks like they spray out water and sweep, but how does the stuff get pulled up and in? How often do they refill them with water; do they do it on the move with a water truck following them, kind of like refilling jets in air? How do they dump the stuff out into dump trucks? Where does all that salt and muck and leaves they sweep up go?

A: Huh. Ask Us Guy has watched the street sweepers go by for decades and has never considered these important questions. By contrast, he’s often wondered how those little nonmotorized Bissell carpet sweepers work, considering they — like street sweepers — don’t have a vacuum component.

Mankato Public Works Director Jeff Johnson forwarded a brochure for the city’s latest street sweeper — the Elgin Road Wizard — and said Streets Supt. Joe Grabianowski could handle the detailed mechanical questions.

So, the answers in the order the questions were asked ... .

Yes, the street sweepers do use water, leaving behind a little wet trail sort of like a slug. But the water is not used for scrubbing the street.

“It’s just for dust control,” Grabianowski said.

So even though the street sweepers can be filled by a water truck, meaning they could technically be refilled on the go like a long-range bomber, they don’t use enough water to make that necessary. Instead, they just swing by the city’s wastewater treatment plant for a load of recycled wastewater or, if the Public Works Center is closer, for a refill there.

“They only have to fill every few hours,” he said.

As for how the sand, bits of trash and other gunk gets pulled up into the machine, it’s basically like a broom and a dust pan. The main brush spins backward as the street sweeper moves down the road, and flings the dirt onto a conveyor belt in the middle of the machine, which carries the sweepings upward into a large hopper behind the cab.

The hopper on the Road Wizard can hold 10,000 pounds of street dirt and can be lifted hydraulically several feet in the air and tipped sideways into a Dumpster. Much of the year, the street sweeper unloads directly to a Dumpster, Grabianowski said. The first sweep of the spring, however, is different. Because of all of the various stuff that’s accumulated on the streets over the four or five months of winter, the sweepers fill up quickly.

“In the spring, we’ll have one to two trucks running between the three brooms that we have,” he said.

The ultimate destination of the crud swept from local streets is the landfill.

Mankato has a pair of Elgin Pelican street sweepers, which have two front wheels that drive the machine and a single back wheel for steering.

The Road Wizard actually has a truck chassis with two diesel engines — one to propel the vehicle and a second one to power the sweepers and conveyor belt. The Road Wizard, which can clean a 10-foot swath of road when all three brushes are operating, can also travel at up to highway speeds when moving from one job to another.

The Pelicans are a little bit smaller in all of their capacities (cleaning swath, hopper size and water tank volume) and have a top speed of 20 mph.

Contact Ask Us at The Free Press, P.O Box 3287, Mankato, MN 56002. Call Mark Fischenich at 344-6321 or email your question to mfischenich@mankatofreepress.com; put Ask Us in the subject line.

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