When operating a turbopump, it is important that you are able to increase the pressure of fluids without causing them to vaporize in the impeller, resulting in various performance losses and issues. In order to effectively raise pressures while ensuring proper operations, one would need to utilize what is known as an inducer. Generally coming in the form of axial types, inducers are placed downstream from the turbopump, ensuring that cavitation is avoided, inlet pressure is lowered, and higher turbopump rotational speeds are permitted. Cavitation is a dangerous issue where vapor bubbles within fluids collapse, causing damage to the impeller, degradation, and potential catastrophic failure.
As cavitation can be detrimental to the health and performance of systems, it is important to utilize parameters that may help one predict when it may occur. One of these parameters is the available net positive suction head (NPSHa) that defines just how much higher the local inlet static pressure is when compared to the local inlet vapor pressure. With NPSHa, it is easier to determine if the various conditions that cavitation requires are present. Meanwhile, the required net positive suction head (NPSHr) is a parameter that is used to describe the inlet head corresponding to specific performance capability drops. During standard operations, the NPSHr parameter will sit around 3% NPSH where the inlet pressure is corresponding to a drop in head rise capability of around 3% while flow rates are at a specific value. When NPSHr values surpass the NPSHa value, one will generally witness various drops in performance as the risk of cavitation increases.
While some applications do not have to worry about these values much based on operational conditions, cavitation conditions are very hard to mitigate when it comes to aircraft fuel pumps, boiler fuel pumps, rocket turbopumps, and other similar machinery that conducts rigorous processes. To ensure that these various pumps work as intended without the major risk of cavitation, inducers are implemented. By installing axial inducers or other inducer types within such pumps, static pressure upstream of the impeller can be bolstered so that the entire system’s NPSHr value is decreased or so that the inlet’s NSPHa value is increased. Either change is roughly just as effective, as both will mitigate the chance of cavitation and its effects.
When choosing between inducers for a particular application, it is important to understand how various properties such as the number of blades and blade geometry can affect operations and conditions. Many inducers will have a small number of blades, such as 3 or 4, and this will allow the blades to be longer so that there is enough space and time to collapse vapor bubbles before they reach the inlet. In other instances, a higher blade solidity may be desired, that of which is achieved with increased blade chord lengths. With higher blade solidity, suction performance can be raised while counteracting oscillations that result from cavitation. By narrowing down the right size impeller for your system, you can better ensure that operations run smoothly without various risks of damage and performance loss.
Here at ASAP NSN Distribution, we offer customers access to over 2 billion new, used, obsolete, and hard-to-find parts that have come from leading manufacturers that we trust. Whether you require an inducer, airplane engine tools, turbopumps, impeller components, and more. All of our offerings are ready for purchase at any time, and customers can kickstart procurement with ease through the submission of an RFQ form as provided on our website. Once received, a member of our staff will reach out to you within 15 minutes or less with a customized quote for your comparisons. Get started today and see how we can act as your strategic sourcing partner.
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