Direction Of Rotation


ABC FIGURE 57A through C Pump assembly and rotation (Reference 7)

Incorrect Rotation Correct rotation of the driver should be verified before it is coupled to the pump (Figure 57). Sections 3 of Figures 52 and 53 show that reversed rotation might produce some positive head and flow rate with pumps of low specific speed, but at very low efficiency. It is unlikely that positive head would be produced by reversed rotation of a high-specific-speed pump.

Reversed Impeller Some double-suction impellers can be mounted reversed on the shaft. If the impeller is accidentally reversed, as at B in Figure 57, the flow rate and efficiency probably will be much reduced and the power consumption increased. Care should be taken to prevent this, as the error might go undetected in some cases until the driver was damaged by overload. Table 1 shows performance data for six pumps with reversed impellers. At least one of these would overload the driver excessively.

Further discussion of abnormal operating conditions may be found in References 7, 12, and 34.

Vibration Vibration caused by flow through wearing rings and by cavitation has been discussed in the foregoing and some remedies indicated. Vibration due to unbalance is not usually serious in horizontal units but may be of major importance in long vertical units, where the discharge column is supported at only one or two points. The structural vibrations may be quite complicated and involve both natural frequencies and higher harmonics. Vibration problems in vertical units should be anticipated during the design stage. If vibration is encountered in existing units, the following steps may help to reduce it: (1) dynamically balance all rotating elements of both pump and motor; (2) increase the rigidity of the main support and of the connection between the motor and the discharge column: (3) change the stiffness of the discharge column to raise or lower natural frequencies as required. A portable vibration analyzer may be helpful in this undertaking. Kovats60 has discussed the analysis of this problem in some detail.

Structural vibrations can occur in most pump types. Typical sources are a) bearing housings—due to the commonly encountered cantilever construction, b) couplings, c) rotor instabilities stemming from excessive ring clearances and consequent loss of Lomakin stiffening of long-shaft multistage pumps, and d) hydraulic unbalance—due to dimensional variations in flow passages and clearances61.

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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