by the vacuum itself. While the valve is open, the resulting differential pressure between atmosphere and vacuum becomes the driving force and transports the wastewater and air towards the vacuum station. Besides these collection chambers, no other manholes, neither for changes in direction, nor for inspection or connection of branch lines, are necessary. High flow velocities keep the system free of any blockages or sedimentation. Large systems with numerous collection chambers benefit from the provision of a monitoring system for remote monitoring of the vacuum valves and sump pits. Such systems allow much faster troubleshooting and easier preventive maintenance of collection chambers and valves. However, monitoring systems are optional systems and not required for operation of vacuum sewer systems. Vacuum sewer systems are considered to be free of ex- and infiltration which allows their use even in water protection areas. For this reason, vacuum sewer lines may even be laid in the same trench as potable water lines (depending on local guidelines). In order to ensure reliable transport, the vacuum sewer line is laid in a saw-tooth (length-) profile. The whole vacuum sewers are filled with air at a pressure of -0.4 to -0.6 bar. The most important aspect for a reliable operation is the air-to-liquid ratio. When a system is well designed, the sewers contain only very small amounts of sewage. The air-to-liquid ratio is usually maintained by collecting liquid/air simultaneously or controller units that adjust their opening times according to the pressure in the system. Sewers can be laid in flat terrain, and parts may flow uphill (within limits). A saw-tooth profile keeps sewer lines shallow; in frost-free climates, trench depth can be about 1.0 – 1.2 m. By contrast, gravity sewers need a monotonically falling slope of at least 0.5 - 1.0%, which can mean that expensive trenching and pumping stations are needed. Once the wastewater arrives in the vacuum collection tank at the vacuum station, it is pumped to the discharge point, which could be either a gravity sewer or the treatment station. As the dwell time of the wastewater inside the system is very short and the wastewater is continuously mixed with air, the sewage is kept fresh and any fouling inside the system is avoided (less H2S). Advantages closed, mechanical/pneumatical controlled system with a central vacuum station. Electrical energy is only needed at this central station no sedimentation due to self-cleansing high velocities spooling