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A vacuum sewer system is a method of transporting sewage from its source to a treatment or disposal facility. It uses the differential pressure between atmospheric pressure and a partial vacuum maintained in the piping network and vacuum station collection vessel. This differential pressure allows a central vacuum station to collect the wastewater of several thousand individual homes, depending on terrain and the local situation. Vacuum sewers take advantage of available natural slope in the terrain and are most economical in flat sandy soils with high ground water. Vacuum sewers were first installed in Europe in 1882 but until the last 30 years it had been relegated to a niche market although it has reamined in use on trains and airplanes. The first applied use of negative pressure drainage (so called vacuum sewerage) was the Dutch engineer Charles Liernur in the second half of the 19th century.〔(1892 Patent: Pneumatic Sewerage system ) sewerhistory.org〕 Technical implementations of vacuum sewerage systems were started after 1959 in Sweden by Joel Liljendahl and afterwards brought onto the market by Electrolux. Nowadays several system suppliers offer a wide range of products for many applications. ==Basic elements== The main components of a vacuum sewrage system are a collection chambers and vacuum valve parts, sewers,a central vacuum station and monitoring and control components. Vacuum technology is based on differential air pressure. Rotary vane vacuum pumps generate an operation pressure of -0.4 to -0.6 bar at the vacuum station, which is also the only element of the vacuum sewerage system that must be supplied with electricity. Interface valves, that are installed inside the collection chambers, work pneumatically. Sewage flows by means of gravity into each house’s collection sump. After a certain fill level inside this sump is reached, the interface valve opens. The impulse to open the valve is usually transferred by a pneumatically (pneumatic pressure created by fill level) controlled controller unit. No electricity is needed to open or close the valve. The energy is provided 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 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 trouble shooting 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, which will be referred to more precisely afterwards. 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 "intelligent" controller units or valves that adjust their opening times according to the pressure in the system. Considering that the vacuum idea relies on external energy for the transport of fluids, sewers can be laid in flat terrain and up to certain limits may also be counter-sloped. The saw-tooth profile keeps sewer lines shallow, lifts minimise trench depth (approx. 1.0 – 1.2 m). In this depth, expensive trenching, as it is the case for gravity sewers with the necessity to install continuously falling slopes of at least 0.5 - 1.0%, is avoided. Lifting stations are not required. Once arrived in the vacuum collection tank at the vacuum station, the wastewater is pumped to the discharge point, which could be a gravity sewer or the treatment station directly. 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). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Vacuum sewer」の詳細全文を読む スポンサード リンク
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