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.
 
 
  1. When the volume of sewage in the vacuum chamber package reaches 40 liters approx.,
  2. The vacuum valve controller detects the water level raising (the 50mm dia, sensor pipe pushes on a diaphragm in the valve controller sensor unit), the vacuum interface valve is actuated (power source not required), and sewage is suctioned into the vacuum pipeline through the suction pipe.
    In the vacuum chamber package, the vacuum interface valve 90mm dia. is set, which is connected to the vacuum pipeline (the main pipeline) via the 90mm dia. connection pipe
    The vacuum pipeline’s diameter varies mainly in the range of 125 to 315 mm.
  3. Sewage suctioned into the vacuum pipeline is mixed with air which is suctioned after sewage, and is transported to the vacuum station. In our SIVAC SYSTEM, sewage is collected to the vacuum chamber package through gravity-flow pipeline as much as it is economical. Therefore, as composite system of gravity-flow system and vacuum sewer system, our SIVAC SYSTEM makes an excellent proposal in terms of LCC (life cycle cost).
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.
*In flat areas where residences are dispersed
*In coast areas with soft ground, flat rock-bed areas, and areas difficult to excavate
The gravity-flow system is suitable to densely-populated areas, while the sewer pump system is adequate to areas with large a variation of gradients. Therefore, it is necessary to examine all these comprehensively.
For the vacuum sewer line, SIVAC SYSTEM recommends the use of polyethylene pipe (HDPE: PE Grade 100). PVC pipe can be also used, but we do not recommend its use in view of LCC and risk of cracking in the future. Where HDPE pipe is used, the vacuum sewer line is free from the risk of damage, and maintains an expected lifetime of 100 years. Further, the vacuum sewer line does not require cleaning work thanks to its self-cleaning function. With these merits, the vacuum sewer line has advantages in operation cost.

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.

 
Vacuum station
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 interface valve itself is actuated at −20kPa.)
Where the pressure loss in the pipeline is small, the degree of vacuum in the collection tank is designed at −50kPa to −60kPa case by case.

 
 
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.
Normally the pumps are made of stainless steel. Mild steel can also be used as the material.
CP type mini vacuum stations are compact vacuum stations.

 
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