Handbook of Civil Engineering Calculations

FIGURE 9. Composite rating chart for a typical centrifugal pump. (Goulds Pumps, Inc.)

6. Evaluate the pump chosen for the installation
   Check the specific speed of a centrifugal pump, using the method given in an earlier cal-
   culation procedure. Once the specific speed is known, the impeller type and approximate
   operating efficiency can be found from Fig. 3.
   Check the piping system, using the method of an earlier calculation procedure, to see
   whether the available net positive suction head equals, or is greater than, the required net
   positive suction head of the pump.
   Determine whether a vertical or horizontal pump is more desirable. From the stand-
   point of floor space occupied, required NPSH, priming, and flexibility in changing the
   pump use, vertical pumps may be preferable to horizontal designs in some installations.
   But where headroom, corrosion, abrasion, and ease of maintenance are important factors,
   horizontal pumps may be preferable.
   As a general guide, single-suction centrifugal pumps handle up to 50 gal/min (3.2 L/s)
   at total heads up to 50 ft (15.2 m); either single- or double-suction pumps are used for the
   flow rates to 1000 gal/min (63.1 L/s) and total heads to 300 ft (91.4 m); beyond these ca-
   pacities and heads, double-suction or multistage pumps are generally used.
   Mechanical seals are becoming more popular for all types of centrifugal pumps in a
   variety of services. Although they are more costly than packing, the mechanical seal re-
   duces pump maintenance costs.

Capacity, L/s

Capacity, gal/min

Total

l*od,m

Total

h*od.

ft