Page 396 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Lube, Seal and Control Oil System Best Practices Be st Practice 7.7

Fig 7.7.5a Centrifugal pump data sheet (Courtesy of The American Petroleum Institute)

volume of a liquid to an equal volume of water at standard con- flow. In the case of bearing wear, a larger ‘equivalent orifice’
ditions) decreases, the energy (head) required to produce the would reduce the pump’s discharge system resistance, and result
same differential pressure increases proportionally. Therefore in increased flow rate. On the other hand, a positive displacement
a positive displacement pump can meet the required energy in- pump will essentially deliver the same flow in the above case. As
crease at essentially the same flow, whereas a dynamic pump we will see in the next chapter, both classifications of pumps
cannot. The only way for a dynamic pump to produce additional present problems in terms of meeting auxiliary system objectives
energy is to lower the flow rate (assuming the pump operates at that will have to be solved using a reliable control scheme.
aconstantspeed). Auxiliary system pump applications involve both viscous
Therefore, increased system energy (head) requirements will (lubricating and sealing oils, etc.) and non-viscous fluids (water).
force a centrifugal pump to a lower flow, or decreased system The viscosity of a fluid is its tendency to resist a shearing force. It
energy (head) requirements will cause it to deliver additional can be thought of as the internal friction that results when one

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