The change in the conveying medium involves two main aspects. First, the variation in the density of the medium. When the density of the fluid being conveyed differs from that of water at standard temperature, the pump's head, flow rate, and efficiency remain essentially unchanged. However, the power required by the pump shaft will vary depending on the density of the fluid. This is because the power is directly related to the weight of the fluid being moved.
Second, the effect of viscous liquids on pump performance. Viscosity has a significant impact on how a pump operates. Factors such as the pump’s design, impeller geometry, and surface roughness all play a role. As the viscosity of the liquid increases, the Reynolds number decreases, leading to higher hydraulic friction losses. This results in a reduction in both the head and flow rate, which is reflected in the Q-H curve shifting downward. However, the head at the shut-off point tends to remain relatively constant. Additionally, the increased friction causes the shaft power to rise, which greatly reduces the pump’s efficiency and may also increase the net positive suction head required (NPSHr). When the viscosity of the liquid exceeds 20 mPa·s, it becomes necessary to adjust or convert the pump’s performance characteristics to ensure accurate operation and prevent inefficiencies or damage.
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