In this respect the water does not present any difficulties, since in this construction the impeller is as a rule located above the highest water level or else a valve is provided on the discharge side. Hence, it is not necessary to dam off or drain any part of the canal.
The pumps of this type can be built for very large capacities. When the impeller of a pump is located above the suction water level it is necessary to draw the line full of water before starting up the pump. Evacuation of the suction line is usually effected by means of a vacuum pump.
Arrangement drawing of a pumping station where a VFD driven axial flow pump (EHT) has been combined with an automatically operating clear discharge canal under the pump.
The figure above shows the arrangement of a horizontal axial flow pump, of which the pump canals are combined with free discharge canals. This is a solution for those cases where the out- side water level is affected by the tides. If the outside water level drops, the valve under the pump (no:3) opens automatically and the water from the polder flows outwards underneath the pump. If the outside water level rises above the polder level, the valve closes automatically. In this arrangement the discharge canal can pass about 2700 cu/m per minute. The design of this pump is based on the results obtained from measurements in respect of models and CFD studies. all performed by our own hydraulic team.
The pump type shown in the picture can be supplied in many versions. The illustration shows a station which during the greater part of the year discharges excess water from a polder into a large river. but in summer “thus in the dry time when the water level in the polder is low” it would be possible to pump the water from the river into the polder. In that case, the same pump can be used for both, drainage and irrigation. Rodelta can constructed the pump so that it can pump in two directions. The direction of flow in the pump can than be reversed.
The pump is driven by a VFD converter/driver this ensures that the flow rate of the pump accurately can be controlled. The construction of the pump is such that no damage can occur with rough operation or when the water contains coarse objects, such as pieces of wood or ice.