12.3.2 Concrete volute pumps
Figure 4.48 shows the sectional arrangement of a typical concrete volute pump, which follows the same hydraulic principles as the conventional metal casing designs except for the volute which is formed on-site on the concrete foundations. The pump casing consists of permanently-embedded top and bottom seating rings separated by the cutwater and stay vanes.
These are carefully positioned over the inlet duct. The assembly then acts as both a sealing ring for the top cover and also as a central location around which the precision-made volute shuttering framework is assembled prior to concrete pouring. The volute shuttering is normally provided by the civil contractor to the pump manufacturer's dimensions, and can be re-used on all pumps on the same contract.
Figure 4.49 shows the various stages of construction of the volute. From experience, it has been found that no special protective coating is required on the concrete to guard against the effects of the water being pumped. Both wear and life expectancy of the concrete are excellent and no problems have been reported on CEGB pumps at inland or coastal stations over a 20 year operating period. A fabricated steel bearing bracket is mounted on top of the pump cover and bolted down and dowelled into position to secure correct alignment. The speed-reducing gparbox is mounted on top of the bearing bracket, with the unit incorporating the pumpset forced lubrication system. The rotating assembly is supported by a combined thrust and journal bearing which can be located within the gearbox. Access to the bottom bearing and mechanical seal is gained from within the tubing.