Vertical Pumps in Power Generation
In power generation, vertical pumps provide design flexibility that is not usually available with other pump types. Nine of 10 Hydraulic Institute-categorized vertically suspended (VS) pump types are suspended with the pumping element below grade, submerged in the pumped liquid.
VS pumps provide a utility that dictates how and when they are used. In addition to other utilities, these pumps require minimum floor space. The pump element is generally submerged, and the depth of the pump setting can be selected so that the net positive suction head available (NPSHa) exceeds the net positive suction head required (NPSHR) at all times. The submerged pump element eliminates the need for priming devices.
Many VS pumps have characteristically steep head-versus-rate-of-flow curves. A steep head curve represents less rate of flow change with respect to changing system head. The pump always operates at the intersection point of the pump and system head curves.
In the range of intermediate specific speed, the maximum pump input power usually coincides with the recommended operating range and will not cause driver overload. However, for high specific speed pumps of axial flow that have respectively low head at high flow rates, the maximum pump input power occurs at reduced flow rates. Care must be taken during start-up and when controlling these pumps to not overload the driver.
For condensate and heater drain applications the VS pumps are typically multi-stage. If design conditions have changed, the staging of the existing pump can typically be changed to better meet current conditions.
For more information on the design and application of vertical pumps, refer to ANSI/HI 2.3 Rotodynamic Vertical Pumps for Radial, Mixed, and Axial Flow Types for Design and Application and be on the lookout for future ANSI/HI 14.3, which is combining HI’s design and application standards for horizontal and vertical pumps into one convenient source.