Self-propelled hydraulic sweepers are familiar sights on city and suburban streets. Although they perform what appear to be relatively unsophisticated and menial jobs, the sweepers accomplish these tasks in minimal time. In one pass, they can sweep up stones, dirt, leaves, paper goods, glass, metal parts, and other waste materials. Sweeper brushes move the material from the street surface and direct it into the machine. A powerful fan inside the machine works like a giant vacuum cleaner to blow the debris into a collection hopper. The hopper is later dumped at a transfer station for subsequent disposal.
Dirt tolerance a must
Because of the heavy demands placed on these machines and the dirty environment in which they operate, some sweepers had a reputation as maintenance intensive — primarily from lack of regular servicing. The street sweeper industry began shedding this image of dated styling, high wear, and the need for frequent maintenance years ago and became more high-technology oriented. Designers have reduced the number of wear components in a typical sweeper and also improved the efficiency and reliability of hydraulics not only for propulsion, but also to rotate the brooms and blower assembly that are the heart of the cleaning system.
Sweepers typically use hydraulic power for all majors functions — hydrostatic propulsion drive, brush and fan rotation, and linear motion for positioning and dumping. One popular design uses a tandem piston pump and a tandem gear pump assembly. Referring to the schematic, section A of the tandem piston pump supplies pressurized fluid to the hydrostatic transmission circuit that propels the sweeper. The second section, pump B, drives hydraulic motor C, which powers the blower. Section D of the tandem gear pump assembly charges pump A, and Section E supplies auxiliary functions on the sweeper. Another gear pump charges pump B.
