CENTRIFUGAL PUMP FOR LUBRICATING OIL DUTIES:

Positive displacement pumps are widely used for lubricating oil duties because of their self - priming ability. This practice is completely satisfactory in installations where the pump speed is variable but when the pump is driven by a constant speed a.c. motor, it is necessary to arrange a bypass which can be closed in to boost flow. By using a centrifugal pump with an extended spindle, such that its impeller can be located at the bottom of the oil tank, the Head/Quantity characteristics of the centrifugal pump can be utilized without the priming disadvantage. Known as the tank type pump this pump has a small open impeller. It can be driven directly by high speed alternating current motor without capacity restrictions whereas the permissible operating speed of the positive displacement type, pumping an incompressible fluid, decreases as the capacity increases.

When the lubricating oil temperature increases, viscosity falls, and from the graph it can be seen that resultant pressure drop for centrifugal pump is much less than that of positive displacement pump as well as there is substantial increase in the amount of discharge for centrifugal pump than the marginal increase in dischage in positive displacement pump.

Thus centrifugal pump placed at a lower level having a suction head is more suitable for lubricating oil duties especially when the lubricating oil temperature increases with the increase in speed of the engine.

Centrifugal pump delivery falls owing to loss of suction due to reasons of insufficient supply head, air leakage in suction pipe, loss of priming facility or leaky shaft gland. Capacity reduction could be result of a damaged sealing ring, leaking gland, obstruction in the line & incorrect rotational speed.

Excessive vibration may be caused by either 1) loose coupling, 2) loose impeller, 3) damaged and 4) impeller imbalance.

INDEX ADV ENG                                                                                                    NEXT