Development of ejector systems for increasing the discharges of centrifugal pumps

Abstract

The pump capability requirement in agriculture especially in rice production is essentially one of low lift end high capacity. Because of the low lift condi¬tions the full capacity of the centrifugal pump cannot be used. By attaching an ejector system* the centrifugal pump is brought to work under the best efficiency condition during low lifts also. Four types of ejector systems were developed and the best one was chosen* based on the capacity ratio and multiplication factor. Experiments were conducted to find out the useful range of suction lifts in which the attachment can be advantageous. Design parameters and efficiency characteristics also were studied. The study revealed that the ejector E2 with primary flow straight and secondary flow inclined at 400 gave higher capacity ratio and multiplication factor than the other three ejectors. Hence E2 was selected for further experiments. For a suction lift of one metre E2 gave a capacity ratio of 3.4 and multiplication factor of 2.6 for the 5 HP centrifugal pumpset. With a 10 HP centrifugal pumpset E2 gave a capacity ratio of 3.6 and multipli¬cation factor 2.8, for a suction lift of one metre. E2 is also having many other advantages than the other three ejector such as easiness of fabrication and fixing. A centrifugal ejector combination requires less capital investment than buying several pumps for use at different heads. Muddy and debris laiden water can be pumped through the ejector system as it has no moving parts. Time of pumping can be reduced by the addition of an ejector system, thus saving power, either electricity or diesel. It can be fabricated in a local workshop and transportation is also very easy. The estimated cost of fabrication of the ejector system is 59.870/-