|VACUUM SEWER TECHNOLOGY|
|Vacuum chamber package|
|Domestic sewage first flows in the vacuum chamber package by gravity-flow. In the vacuum chamber package are installed the vacuum interface valve units (composed of the vacuum interface valve and vacuum valve controller), sensor pipe of 50mm dia., and suction pipe which is of the same diameter as the vacuum interface valve. The gravity-flow pipeline as well as air intake pipe and pole and breather pipe for air supply are connected to the vacuum chamber package.
|Vacuum sewer line (1)|
|Polyethylene pipes with electro fusion joints are?usually used for anti-earthquake shock, are extremely tight and have longer life even under exposure to atmosphere.|
|In accordance with SIVAC Technical Manual, the vacuum sewer line consists of 2 lines; one is a pipeline with a 0.1 − 0.2% down-gradient, and the other with an up-gradient in the saw tooth profile which is called “lift”. This method enables the pipeline installation according to the local topography, whether the topography is flat or slightly up-gradient.
The down-gradient pipeline is also possible according to the topography, in the same manner as the gravity-flow system. Underground obstacles and water channels can be avoided by the lift. Unexpected obstacles during the installation works can also be avoided easily. Therefore, the vacuum sewer line has advantages in installation cost.
In general, the collectable distance of sewage from the vacuum station is 2 − 4 km. It can be extended to 5km approx. depending on the local topography or sewage collected is small in volume.
In view of the nature of pipe installation, the vacuum sewer system is most suitable to the areas with the following conditions.
|Vacuum sewer line (2)|
|In the vacuum sewer system, the sewage collection scope is determined by the vacuum loss, which is divided into two: the lift loss and friction loss. In the past, SIVAC SYSTEM as well as other vacuum sewer systems worked out designs using the same calculation method regarding these losses.
Now, the automatic air breathing system which is our patented technology developed under SIVAC SYSTEM, overrides the common knowledge in conventional vacuum sewer systems, and enables innovative pipeline design. Depending on the conditions, the collectable distance can be made nearly double of the ordinary distance, widely extending the application scope of the vacuum sewer systems.
economical operation of the system by low air/liquid ratio.
|The vacuum station functions to run the vacuum pump intermittently and maintain the vacuum sewer line in vacuum condition at all times. Air collected from the vacuum sewer line is exhausted, and sewage is collected in the collection tank. Then, sewage is pumped to the main sewer pipeline and treatment facility by the sewer pump. The vacuum station is similar in function to a lift station in the gravity-flow sewer system.
2 or 3 vacuum pumps are required for 1 collection tank. Vacuum is generated by running 1 pump or 2 pumps simultaneously Actuation is controlled by the control panel. The degree of vacuum in the collection tank is maintained at −60kPa to −70kPa normally. The pipeline is so designed that −25kPa degree of vacuum reaches the end of the vacuum sewer line when the degree of vacuum in the collection tank is −60kPa. −25kPa is the vacuum pressure, at which the vacuum interface valve actuates suctioning safely.
|The vacuum pump is not actuated unless the degree of vacuum in the collection tank falls down to the designated level. Therefore, it is not running continually but intermittently. In the 2-pump type, the pumps are operated alternately. In the 3-pump type is the type, 2 pumps are operated simultaneously at peak flow. This type is adopted where it is possible to reduce more total cost, in initial cost and operation cost, compared to the 2-pump type. In any case, 1 pump at least is not in the status of actuation.
In general, vacuum valves with the capacity of 1.5kW to 18.5kw are used. In Japan, most of them are made of anti-corrosive material such as SUS. NIKUNI water circulating type vacuum pumps and ANLET roots type vacuum pumps are the examples. The aqua type of BUSCH rotary vane type vacuum pumps is also used.
As regards the sewage pumps, 2 pumps are operated alternately. The capacities are determined by the sewage volume at the peak flow and the head required for pumping the sewage. The collection tank capacity is to be selected according to the application, in the range of small size 1.23 to large size 18m3.