Vacuum sewers are a cost-effective, environmentally friendly alternative to traditional gravity sewers providing low maintenance, efficient and reliable sewage collection. The typical applications for the vacuum sewer system are:
- Flat terrain
- Expanded municipalities, residential, tourist, industrial and commercial areas, harbors, marinas
- High ground water tables
- Trenching in rocky and sandy environment
- Trenching in archaeological sites
- Ecologically sensitive areas (ground water)
Public works directors and civil engineers who are unfamiliar with vacuum technology may think that the systems are complex and fragile. In fact, the opposite is true. Vacuum systems operate on simple principals of physics and have proven over many years to be extremely reliable.
Homeowners usually don’t notice the difference between vacuum sewers and other systems because gravity is used to transport wastewater from the home or business to first collection point, the vacuum valve pit, which is usually buried near the street. The valve pit consists of a small collection sump (made by PE or GRP or other plastics – concrete is obsolete) and a pneumatic vacuum valve mechanism located in a chamber above the sump. One or more houses (up to five) are typically connected to a single valve pit.
When the wastewater in the valve pit sump reaches a predetermined level, usually around 40 litres, it triggers the pneumatic valve that releases the wastewater into the vacuum main where negative pressure propels it at speeds up to 6 meters per second toward the vacuum station. The speed of the air and wastewater mixture helps scour the line and break up solids.
The piping network connects the individual valve pits to the collection tank at the vacuum station. SDR 11 HDPE pipes with electrofusion coupling or SDR 21 PVC pipes solvent glued or with special O-ring gaskets made for vacuum use, are typically used. Typical sizes include pipes from d90 up to d250. Lifts or vertical profile changes are used to maintain constant shallow trench depths (typically 0.8–1.2 m) as well as for uphill liquid transport.
Resilient wedge gate valves (division valves) are used to isolate various sections of vacuum mains thereby allowing operation personnel to troubleshoot maintenance problems in a timely fashion. Also, inspection pipes allow simple leakage detection during construction as well as during the operation of a vacuum sewer system. Inspection pipes enable the insertion of inflatable test balls for precise leak detection. The vertical inspection pipes are sealed by a special rubber cap and are protected by a cast iron cover.
A vacuum station functions as a transition point between a vacuum collection network and a forcemain leading directly or indirectly to a treatment facility. The wastewater from the vacuum mains is discharged into the collection tank which is a sealed, vacuum-tight vessel made of special coated steel or stainless steel to avoid local corrosion. Vacuum gauges are used on all incoming lines to allow the operator to monitor the vacuum levels of each vacuum main.
The bottom portion of the tank acts as the wet well. Wastewater is stored here until a sufficient volume accumulates, at which point the tank is evacuated by the discharge pumps. The discharge pumps are typically non-clog, suitable for sewage and slurry applications, submerged or dry-mounted pumps (depending of the installation). Redundancy is required, with each pump capable of providing 100% of the design capacity.
Vacuum, produced by the vacuum pumps, is transferred to the vacuum mains through the top part of the tank. Vacuum pumps typically are rotary vane or liquid ring type. Redundancy is required, as design capacity must be met with one pump out of service.
As a result of airborne H2S in the vacuum pump discharge, odour may be a concern at the position of the vacuum
The control panel of the station consisting of contactors, starters, disconnect instruments, switches, touch screen panel, terminal boards, and wiring to control and interlock contacts for operation of discharge pumps and vacuum pumps. A touch panel is used for setting up the parameters and overviewing of the functions (HMI). The collection tank level control and fault monitoring equipment are also normally located within the vacuum system control panel.
The chamber monitoring system facilitates a reliable control of the operation of collection chambers, in a vacuum sewage system. The collection chamber monitoring system reduces the time involved during routine controls and simplifies trouble shooting. It facilitates minimization of time in case of clogging inside the collection chamber and reports the consequent congestion inside the inlet pipe. In addition, the chamber monitoring modules are provided with a self-controlling function. If a permanently occurring signal is interrupted due to a fault, a failure message for the respective chamber is reported.
The vacuum station materials of construction are the choice of the consulting engineer and typically are selected to match the architecture of the surrounding community.
The following services are provided by our experts:
- Feasibility studies
- Preliminary study
- Final design
- Tender documents
- Project management
- Construction management
- Technical support
Our services cover all the area of vacuum sewer systems according to international and local standards. We can provide our services according to the valve pit sump and pneumatic vacuum valve of our client’s choice. Our results are in accordance with the equipment that is produced all over the word.
Guidelines for design and operation of vacuum sewer systems are given in the technical norms:
EN 1091 (European Standard)
DWA-A 116-1 (German Standard)
EPA/625/1-91/024 (US Standard)