Pumps net positive suction head

Pump Net Positive Suction Head. A pump with a high OTSH requirement pushes equipment to a higher elevation, increasing the cost of piping and supports. On the other hand, a pump with a lower NPSH may cost more. The difference in support and piping costs must be considered in the selection of a more expensive pump with a lower NPSH. 

Exhibit 4-27 illustrates how primary process considerations govern the elevation of the surface condenser and some of its auxiliary equipment. Because a pump is needed to remove the condensate from the hot well, the pump net positive suction head (NPSH) must be satisfied to operate satisfactorily. Vertical pumps are generally used in this application because the NPSH requirement is calculated from the bottom of the lower impeller for vertical pumps, compared with the centerline of the inlet nozzle for horizontal pumps. Setting the elevation of the inter-after condenser, usually located to the side of the suifice condenser, can be done with fewer restriaions. Ilie bottom of the inter-after condenser shell must not be more than 3 ft (900 mm) below the condensate return nozzle on the side of the hot well. The plant layout designer is then free to set the elevation as high as necessary. 

A preliminary analysis of the two reactor concepts, single-fluid and two-fluid, resulted in the decision to use three external loops for the singlefluid and six for the two-fluid reactor. Por both these alternates the maintenance philosophy selected was that of removal and replacement by horizontal transfer of a complete primary loop upon failure of any major component in the loop [5]. Thus, for arrangement purposes, the primary loops assume the shape of a rail-mounted horizontal containment vessel, or capsule, sized to contain all loop components. The height of the capsules relati e to the leactor is dictated by an economic balance between height or elewition costs and pump net positive suction head. 

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