Dewatering pump
Dewatering pumps are centrifugal pumps installed in a building that is situated below the groundwater level, to reduce the water level and then maintain it at this level.
One example is in underground mining in which water penetrating into the adits is pumped up to the surface. In open-cast mining, the groundwater level is reduced through drainage well trenches until the pit is dry. The groundwater level in construction pits in civil engineering is reduced in a similar way.
In underground mining, the flow rates (Q) can attain up to 900 m3/h and the heads (H) up to 1050 m; in open-cast mining up to 1800 m3/h and up to 400 m. It is technically feasible to go beyond these limits.
Heads over 1000 m require the use of multistage pumps with single-entry impellers facing the same way or in opposite directions, or with double-entry impellers. See Fig. 17, 18 and 19 impellers
As such water often contains solids and suspended solids (the results of erosion) and is often chemically corrosive (see Material selection) impellers with wide channels, shaft protecting sleeves and wear-resistant or corrosion-resistant materials (see Chemical resistance table) are used.
Dewatering pumps installed as horizontal pumps in dry installation usually have no suction head. They are driven by electric motors suitable for operation in potentially explosive atmospheres. Vertical pumps in the form of submersible borehole pumps offer many benefits for automatically operated dewatering systems. The submersible motor is filled with water and positioned beneath the pumps, flooded and thus adequately cooled. Flameproofing is only required for the cable connections.
In open-cast mining, drainage well trenches equipped with submersible borehole pumps are arranged at the edge of the workings and also in the various levels in a staggered arrangement.
The submersible borehole pumps can also be built for high voltages of 3 or 6 kV (in some cases up to 10 kV) as well as for low voltages.
For dewatering or reducing groundwater on large building sites, protection is provided by drainage well trenches equipped with submersible motor pumps in excavations such as for underground railways, bridges or in open-cast mining. Portable submersible motor pumps are often used for pumping out heavily contaminated seepage water in such cases. With the latter type of pump, the motor is arranged above the pump. Their impellers are specially designed to handle waste water (see Waste water pump). A mechanical sealing element protects the motor against the ingress of water. The motor cooling is adequately scaled to enable the pump set to also run when not submerged in water.
