Piping issues at the inlet line of centrifugal pumps
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As shown in the image, I would like to ask why the vertical entry at the pipe elbow should be as short as possible? May I ask again, why is the diameter of the inlet pipe always greater than or equal to that of the pump’s first and second stages? Please, dear experts, help to answer this
It’s not that the bend in the suction pipe should be as short as possible; rather, the entire suction pipe should be as short as possible, as this helps to reduce the pressure losses along the inlet, thereby minimizing the pressure drop of the liquid at the pump inlet and preventing cavitation in the pump. As for the issue of diameter changes at the inlet: in order for the pipeline diameter to conform to standard values, the flow velocity of the liquid within the pipeline is reduced (to the economic flow velocity), which in turn reduces the losses caused by high flow velocities. Therefore, the diameter of the pipelines is generally larger than that of the pump’s inlet and outlet ports, and it is necessary to use transition fittings at these points to adjust the dimensions accordingly. The flow velocity of the liquid as it passes through the pump changes in the following manner: slow (inlet pipeline) – acceleration (inlet reducer) – maximum velocity (outside diameter of the impeller) – deceleration (volute channel of the pump casing) – further deceleration (diffuser of the pump casing) – further deceleration (exit reducer) – slow (exit pipeline). A centrifugal pump works by using the rotation of the impeller to increase the velocity of the liquid, and then gradually reducing this velocity to convert it into pressure. To achieve this, it is necessary to reduce and then increase the area through which the liquid flows. If a diffuser tube is not used and different pipe diameters are connected directly to each other, the sudden change in area results in significant local hydraulic losses, **reducing the efficiency of the pump. Therefore, a tapered tube is used to achieve a gradual transition, thereby minimizing losses. It is reasonable for the diffusion cone angle of the diffusion tube (not the one-sided slope) to be between 6–10°. Moreover, the diffusion losses are much greater than the contraction losses; hence, it is essential to control the cone angle of the outlet diffusion tube carefully.
Detailed explanation of the piping for the centrifugal pump inlet line; I learned a lot from it