Updated: July 2002

1. Purpose

In the recent years, the promotion of the sewer system construction for the rural districts has been much urged with the environmental and life style improvement reasons. These districts are characterized by low population, flat ground surface, etc. A sewer system more suitable to these districts as compared with the conventional gravity sewer system has been requested. In the vacuum sewer system, the sewer pipelines are kept in vacuum and the sewage is transferred by pressure difference. With this peculiar transfer principle, the sewer construction cost is much saved and the sewer economy is greatly improved as compared with the conventional gravity sewer system. The vacuum sewer system is suitable for the rural districts or for the comparatively small sewer system size.

2. Features

1) Construction cost saving of sewer system
The vacuum pipeline can be located in shallow and narrow trench and the sewer construction cost is much saved as compared with the conventional gravity sewer system which usually requires deeper and bigger trench for pipeline. The construction public nuisance is also minimized.
2) Pipeline positioned along the ground surface geometry. The vacuum pipeline consists of down grade stops and upward lifts. Thus the pipeline can be positioned along the ground surface geometry up and down.
3) Application of smaller sized pipe diameter
Thanks to the specific sewage transfer principle of two phase flow, the pipe diameter can be cut into min. 75 mm and typically 100mm.
4) Booster pump stations not required
The vacuum sewer system can transfer sewage without a help of booster pump station. Thus electric supply is required only at the vacuum station.
5) Without sediment and clogging in the pipeline
The sewage is transferred unsteadily and with high flow velocity, thus the pipeline is always clean without sediment and a risk of clogging.
6) No leakage
The pipeline is air-tight and is kept in vacuum. There is neither sewage leakage from the pipeline nor underground water intrusion into the pipeline.

3. System Components

The vacuum sewer system consists of the vacuum valve unit, the vacuum pipeline and the vacuum station. Reference is made to system flow sheet.
1) Vacuum valve unit
The sewage from the houses and buildings flows into the vacuum valve unit by gravity. When the sewage quantity reaches to a certain level, the water level controller is triggered to open the vacuum valve and the sewage is sucked into the vacuum pipeline. The vacuum valve is operated automatically by the vacuum pressure in the pipeline and electric supply is not required.
2) Vacuum pipeline
The sewage is sucked into the pipeline together with the air at the valve units. The sewage and the air are intensively mixed up in the vacuum pipeline and transferred into the vacuum station. Thus the sewage is supplied with sufficient oxygen and the generation of dangerous and harmful gas is avoided. Isolation valves are installed every approx. 400m distance for maintenance purpose in the pipeline. Maintenance manholes as in the case for the conventional gravity sewer system are not required at all. The vacuum pipeline consisting of the down grade slopes (0.3%) and the upward lifts can be positioned along the ground surface geometry and can avoid various obstacles underground.
3) Vacuum station
Vacuum is generated in the vacuum station and the sewage in the pipeline is sucked into the collecting pit or tank in the vacuum station. The collected sewage is transferred by pumps to a sewage treatment plant. There are two options as for vacuum generation. The one is ejector system and the other vacuum pump. With the ejector system, the sewage in the collecting pit is recirculated by the circulation pumps through the special ejector which generates the vacuum.