The S-shaped head-versus-flow curve in Fig. occursin some axial-flow pumps. Explain how a fairly flat systemloss curve might cause instabilities in the operation of thepump. How might we avoid instability?
The S-shaped head-versus-flow curve in Fig. occurs
in some axial-flow pumps. Explain how a fairly flat system
loss curve might cause instabilities in the operation of the
pump. How might we avoid instability?
Usually, there is a potential risk of instability when the pump head curve slope, dH / dQ, is -ve except if two such points exist. From the above figure, curves cross at three points (a, b, c). Out of these 3 points, point b is statically unstable and cannot be maintained. When a small disturbance is considered near point b, suppose the flow rate drops lightly, then the system head will decrease, but the pump head will decrease more. Furthermore, the flow rate will decrease, and we move away from the operating point, which therefore is unstable.
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