The litter is scavenged towards the suction head either at the roadside of the truck or in the centre of the sweeper than drawn by air as a vacuum into the debris hopper. As the air and debris flow up the suction pipe water is injected to suppress dust and wet the debris so that it will settle out of the air stream once it spins in the hopper. The air is then drawn through screens or filters before being pumped to atmosphere. There are three types of air suction machines
A mulching fan where the air and debris is passed through a mulching fan which crashes the debris before it goes into the hopper, these machines are good for bulky light weight litter such as papers and cans and bottles.
Clean fan suction sweepers have the fan above the hopper creating a clean vacuum, which draws the debris into the hopper and it is compressed by air movement and wetting. These sweepers can be cleaner and are advantageous where particles are best kept un-ruptured, such as seedpods from trees, which can create allergies. The clean fan should be quieter in operation as it is a larger diameter hence needs to spin less to create the same vacuum and does not have the mulching noise.
The third type of vacuum or suction sweeper is commonly referred to as regenerative air. Some do not consider these as a suction sweeper, although this is misleading as the debris is carried to the hopper by suction. The only difference is that the scavenging of the litter towards the suction head is done in an enclosed box or sweep head and the debris is moved by recycled air rather than a broom.
This has several advantages over a broom. There are a few moving parts under the truck and the sweeping action is carried out by air, which on other designs normally is wasted to atmosphere. This air can reach fine holes and cracks that a broom cannot. No broom wear, because there is no main broom only side brooms.