337

Single

UNIVERSAL SPECIFIC SPEED O0

UNIVERSAL SPECIFIC SPEED O0

SPECIFIC SPEED IN THOUSANDS(USCS)

FIGURE 11 Power balance for double-suction pumps at best efficiency (Reference 12)

SPECIFIC SPEED IN THOUSANDS(USCS)

FIGURE 11 Power balance for double-suction pumps at best efficiency (Reference 12)

and wear increase with increasing speed, particularly if the liquid contains solid particles in suspension. The danger of cavitation damage usually increases with increasing speed unless certain suction requirements can be met, as described later.

Effects of Specific Speed Figues 6 and 11 show that maximum efficiency is obtained in the range 2000 (0.73) < ns < 3000 (1.10), but this is not the only criterion. Pumps for high heads and small flow rates occupy the range 500 (0.18) < ns < 1000 (0.37). At the other extreme, pumps for very low heads and large flow rates may have ns = 15,000 (5.49) or higher. For given head and flow rate, the pump having the highest specific speed that will meet the requirements probably will be the smallest and least expensive. However, Figure 9 of Section 2.1 shows that it will run at the highest speed and be subject to maximum wear and cavitation damage, as previously mentioned.

Effects of Clearance wearing-ring clearance Details of wearing-ring construction are given in Subsection 2.2.1. Schematic outlines of two designs of rings are shown in Figure 12. The L-shaped construction shown in Figure 12a is very widely used with the close clearance between the cylindrical portions of the rings. Leakage losses increase and pump performance

(b) SINGLE LABYRINTH FIGURE 12A and B Typical wearing rings

TABLE 3 Effects of increased wearing-ring clearance on centrifugal pump performance

Specific speed n (O,)

Ring clearance, % of normal value

Percent of values at shutoff with normal ring clearance

Percent of values at best efficiency with normal ring clearance

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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