Why does API 610 recommend specific margin i.e. 25%, 15% & 10% for selecting motor rating over pump rated bkw?
The basic reason for specifying motor rating above that of the BkW of Pump, API or no API, is that the duty conditions themselves are not rigidly fixed. e.g. variations in discharge head, suction conditions, viscosity, temperature -all can affect the duty conditions. In centrifugal pumps a lower head will result in shifting the duty point to the right of BE,P or original duty point. This will invariably reflect as higher BkW. A change in the S.G. of liquid directly affects the BkW. Basically to take care of these variations a margin in the Motor rating is desired. These values have been arrived in consultation with the users and manufacturers.
