Pump Inducer – Its significant role in pump operating

by Barkha Pahuja SEO/Writer Pumps need a certain amount of pressure to be able to operate properly.  To ensure long service life the pump selected must be able to function without excessive cavitation, which is what occurs when suction pressure drops too far producing tiny bubbles within the liquid that burst and cause damage to the internal pump gears (including impellers, shaft, etc.). What happens when a condition arises where you cannot find the ‘perfect’ pump to meet the suction circumstances of an exact application? One existing alternative is to use a pump inducer. A pump inducer is a component that can be added to the axial inlet portion of a centrifugal pump rotor, the purpose of which is to raise the inlet head by an amount enough to provide the obligatory pressure and prevent substantial cavitation in the pump.

Why inducer is important in a pump
An important reduction of the required NPSH value using an inducer can only be accomplished under low flow conditions. As a result, the functioning range of a pump fitted with an inducer is limited when associated with a pump without an inducer.

To evade blockage of the flow cross-sections by vapour bubbles (see Cavitation) in the inducer on the vane pressure sides, the inducer should be sized for higher performance than essentially obligatory for the desired operating range. It will therefore function in the low flow range at almost all possible operating points and be able to offer the pump impeller with the obligatory inlet pressure (see Characteristic curve).

Under dangerous low-flow conditions, low-frequency pressure variations, typical for inducers, can be observed. This is due to cavitation and changing approach flows.

The flow separation on the vane's suction side which may happen under certain circumstances during the low flow process is far less of a problem than flow parting on the vane pressure side, which generally leads to the collapse of the head in the case of axial impellers.

The pump head plays a significant part in the calculation of the efficiency of a pump armed with an inducer. The inducer functions under conditions of substantial entry shock (see Shock loss in the low flow range) and therefore at a lower productivity than the pump impeller. The ratio between the inducer head and pump impeller head is significant as the deterioration of the proficiency of the whole unit, i.e. the inducer and the pump is extremely dependent on this ratio. It follows that the provision of an inducer on pumps with a low precise speed (high head) is less damaging to efficiency than in the case of high specific speed pumps.

Different types of Inducer designs

Helical surface: the head is completely made by the vanes ‘occurrence angles (for inducers with a low head).

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Created on Apr 2nd 2024 05:18. Viewed 56 times.

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