GW Kanalabsperrung always has a selection of these systems stored at its company headquarters in Wesel, Germany. These systems are rented to companies and municipalities having problems with water tables that are too high and need to be lowered during the construction phase for underground construction, pipeline construction or sewerage construction. In the process, GW Kanalabsperrung offers its customers customized service that includes installation of the system with all filters and hose lines through to daily monitoring of functionality and correct operation. This has enabled GW Kanalabsperrung to build up a customer base throughout the entire state of North Rhine-Westphalia.
Until now, systems from different manufacturers were sold. In 2015, Managing Director Gerhard Wagner himself developed a new system and, after many years of experience with different vacuum pumps, he decided to use the Mink claw vacuum technology from Busch. Whilst the first systems were delivered to customers last year, GW Kanalabsperrung unveiled this new system approach to a larger audience of specialists for the first time at Bauma 2016 in Munich.
Gerhard Wagner had been involved in the topic of groundwater lowering long before the company was founded. Working with vacuum methods basically follows the same principle (fig. 1). To prevent groundwater from penetrating an excavation pit or, alternatively, to prevent an excavation pit from having to be drained, suction pipes with filters are placed around the pit one to two metres apart from each other. These can be up to six to seven metres deep in the ground. The number of these suction pipes, their distance from one another and the filters used depend on ground conditions.
Fig. 2: The operating principle of the vacuum method for groundwater lowering: 1 Groundwater lowering system, 2 Manifold, 3 Excavation, 4 Suction pipe, 5 Suction filter, 6 Groundwater
All suction pipes are connected to the groundwater lowering system using a manifold. This groundwater lowering system always consists of one or two vacuum pumps, a vacuum container and one or two water pumps as well as a control system. When the system is turned on, the vacuum pumps pump all the air out of the container and the entire pipe network. The vacuum created by this process sucks groundwater from the vicinity of the individual filters, which lowers the overall water table. The water is sucked into the container by the vacuum. As soon as a certain level is reached in the container, the water pump, usually a centrifugal or submersible pump, begins to pump the water out of the container and directs it into the sewer system or a body of water via a hose.
Once the level of water in the container is reduced to a minimum, the water pump shuts off and the vacuum once again sucks groundwater into the vacuum container. This process repeats itself constantly around the clock to ensure that the excavation pit is drained during the construction phase. Depending on how long the excavation lasts, this process can go on for weeks to months.
The liquid ring vacuum pumps often used for this process have the drawback that they require water as an operating fluid. This water is continuously fed into the liquid ring vacuum pump by way of an internal circulation system. In the process, the amount of water must be checked regularly to ensure that the pump does not run dry, which would lead to pump failure. Despite circulatory operation, fresh water must be regularly fed into the system during operation of the liquid ring vacuum pump. In practice, this can be difficult during excavation work. Groundwater that has been sucked in must not enter this circulatory system in any case because, despite filtering, groundwater often carries fine and abrasive sand that quickly causes wear on the liquid ring vacuum pumps.
Fig. 3: Cross section of a dry, non-contact Mink claw vacuum pump
Up to now, Gerhard Wagner mainly used oil-lubricated rotary vane vacuum pumps to lower groundwater. They are reliable. However, they require a certain level of maintenance. Dry-running rotary vane vacuum pumps turned out to be completely unsuitable. Whereas the oil in oil-lubricated rotary vane vacuum pumps creates a protective film inside the pump, protecting it against corrosion, dry-running rotary vane vacuum pumps always risk becoming corroded during downtimes, in which case they fail to start. Even after a break in operation of only one day, the vanes can become stuck in the rotor. When starting, they can break and lead to greater damage inside the vacuum pump.
In his new groundwater lowering systems, Gerhard Wagner depends on claw vacuum technology from Busch. Up to now it has provided the best results. The minimum maintenance effort in particular makes them interesting for this application. Because it is no longer necessary to check the vacuum pump daily, which can be very costly and take up a lot of time - for example, if a construction site is not being worked on after a cellar is cemented or at the weekend, if an employee has to make an extra trip to the construction site to check if the system is working correctly. The low maintenance effort is possible because Mink claw vacuum pumps feature operation fluid-free and non-contact compression. This means that there is no operating fluid like water or oil in the compression chambers in these pumps. All monitoring and maintenance work relating to operating fluids is theredore completely unnecessary. The risk of failure if there is too little water in the liquid ring vacuum pump or due to condensation from moisture sucked in with the oil in the vacuum pump no longer exists. Moreover, there is no wear due to the non-contact operation method. This means that parts do not have to be exchanged and individual parts inside the pump cannot seize up due to corrosion. The maintenance effort for Mink claw vacuum pumps is limited solely to an annual gearbox oil change.
The new GWA groundwater lowering systems from GW Kanalabsperrung are available in four versions. All versions consist of a vacuum container with a volume of one cubic metre. Inside, a waste water submerged pump is installed horizontally. This pump's capacity is 90 cubic metres per hour. Three Mink claw vacuum pump sizes can be selected for vacuum supply, with pumping speeds of 80, 100 or 140 cubic metres per hour, depending on how many suction pipes are connected or the amount of water that needs to be sucked in. The system with the smallest Mink claw vacuum pump and 80 cubic metre per hour pumping speed is also available with a built-in control system and frequency control. This makes it possible to control the system so that constant pumping speed or constant vacuum level can be maintained independently of changing operating conditions. This is an advantage if the conditions change during the operating time and the vacuum pump automatically adjusts the pumping speed. In addition, the conveying performance can be set individually at the place of use during installation. This enables the system to be precisely set or readjusted for the conditions on site, or it adjusts itself automatically. During the first field test, Gerhard Wagner discovered a further advantage of using the claw vacuum technology from Busch: the Mink vacuum pump is significantly more energy-efficient than all other mechanical vacuum pumps on the market. This efficiency can be increased further by using frequency control. The new GWA groundwater lowering systems can also be used for vacuum deep wells.
In the process, a vacuum can additionally be applied to the well from the top surface down.The vacuum primarily ensures faster and far-reaching better drainage and stabilization of the new ground floor if the ground has bad permeability.
About GW Kanalabsperrung
The GW Kanalabsperrung company was founded in 2005 and deals with the sale and rental of equipment used to cut off sewers like sealing balloons, shut-off plates or sealing collars as well as systems that use vacuum methods to lower groundwater.