An example of how to deal with a typical NPSH problem is shown in below. The required NPSH in this example is 22 ft (6,700 mm).
If a horizontal pump is used, the bottom tangent line of vessel A must be a minimum of 22 ft (6,700 mm) above the centreline elevation of the shaft.
If a vertical pump, is used, the vessel Bottom tangent line is located closer to grade because NPSH is calculated from the bottom impeller of the pump located below grade.
Although vertical pumps require less of at vessel support structure and possibly less piping, they are more expensive to buy and maintain.
Therefore, a horizontal pump application is at more desirable solution in this instance.
Vertical pumps are better used to draw suction from large surface condensors that service large compressors.