"When a regenerative air sweeper is operated in full regenerative mode, fine silt can be impacted into the pores of the surface with the air blast - especially if the surface is damp - so you need to operate carefully," Giles says. "In the full vacuum mode, the vacuum level will not restore a clogged surface, but may provide acceptable maintenance cleaning."
Pure Vacuum Sweepers Pure vacuum sweepers account for approximately 5% of the U.S. sweeper market. They operate like a giant vacuum cleaner, removing debris off the surface and depositing it into a debris hopper. The fan air is then simply exhausted out of the body. Water in the hopper or at the side brooms is used to prevent fine particles from being pulled through the vacuum fan and being exhausted into the free air.
Giles says Elgin's Whirlwind, for example, can deliver a high vacuum level of water - up to 80 in. "Most porous pavements, and many interlocking block surfaces, require this degree of vacuum to restore infiltration of a clogged area."
The silt that plugs both types of surfaces is generally carried there by water. When damp, the silt swells and has a sticky texture to it. Removing silt from the pavement is best done when the surface is dry enough for the silt to contract and release its grip on the surrounding material.
"Both regenerative air and pure vacuum sweepers are designed to dampen the surface with a water spray to reduce airborne dust," Giles says, adding that sweeper hoppers can be preloaded with a few hundred gallons of water to eliminate carryover dust through the vacuum fan.
Maintenance cleaning of block areas can be done with a regenerative air sweeper or a vacuum sweeper. Giles cautions that both sweepers should be operated at low power levels to remove the loose surface material without disturbing the granular filler in interlocking paver blocks.
Determining when restoration of the surface is required depends on the composition of the surrounding soil. In areas with very sandy soil the surfaces will last longer; while surfaces in areas with a high degree of clay in the soil will clog rather quickly. Visual inspection will determine when and if remedial action is needed to increase percolation in the paver openings.
When surface restoration is required, Giles says the top layer of granular material containing the silt plug can be effectively removed with a pure vacuum sweeper. While the granular material is generally inexpensive and easily replaced it's important to determine the cost and availability of replacement filler ahead of time before a complete restoration is attempted.
With 40 years' experience in the sweeping industry, Mark Kinter, technical consultant for Elgin Sweeper Co., has partnered with the EPA, several universities, surface manufacturers, end users, and equipment suppliers to understand the requirements of porous surface maintenance.