ACU-VAC (Vacuum Flushing System)

Range of Application

The ACU-VAC Vacuum Flushing System is designed to flush storm water, surface water, combined sewage/storm, raw sewage storage tanks, and equalization basins. The ACU-VAC can be used in circular storm tanks (up to 65m diameter), rectangular storm tanks (up to 150m in length), and sewer networks (up to 250m in length).

The ACU-VAC is designed to have a tank floor gradient between 0.5-2%. Circular tanks with a diameter of 165 ft (50m) or more can use the ACU-VAC Vacuum Flushing System.


  • No submerged moving parts; all parts are serviceable without entering the tank
  • Full flushing action even after small spills
  • High cleaning performance
  • Optimal flushing effect for tanks up to 60m diameter
  • No separate water supply required. System is
    flushed with storm water
  • Low energy consumption
  • Minimal maintenance
  • No maintenance within the tank for greater health and safety
  • Potential for separate “dry” flush with external water supply
  • Automatic operation
  • Peripheral sump flushing for tanks greater than 30m in diameter
  • Robust design

System Operation

Initially, the ACU-VAC tank and flushing chamber are empty (Step 1). When a storm occurs, combined sewage and rainwater spill into the storage chamber and rise above the siphon level of the inlet to the flushing system (Step 2). Then, the vacuum pump automatically starts drawing water from the storage chamber into the flushing chamber until the maximum level in the flush chamber is reached (Step 3).

When the storm subsides and the storage chamber empties, sludge and other sewage related debris accumulate on the chamber floor. During the entire process, the level in the flushing chamber is held under vacuum (Step 4). Once the tank is empty, the flushing sequence starts automatically; the vacuum seal is broken and a large volume of water surges from the flushing chamber, flushing all the solids from the chamber floor (Step 5). The entire process can be viewed below.