Why are the inlet and outlet diameters of the centrifugal pump set to be so large?
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This post was last edited by luoheng116 on 2010-9-7 at 11:57. While carrying out the preliminary selection of LNG pumps today, I encountered a problem that has been bothering me: the client requested a flow rate of 10,000 standard cubic feet per hour, with an inlet pressure of 2 to 5 kilograms and an outlet pressure of around 11 kilograms (I haven’t listed some other technical requirements). At the client’s request, we selected an LNG submersible pump from the Italian company Vanzetti for them. The inlet and outlet diameters of this pump are DN65 and DN32 respectively. 10,000 standard cubic feet is equivalent to a liquid flow rate of 16 cubic meters (the gas-to-liquid ratio of LNG is 625; 10,000/625 = 16). Using a pressure difference of 0.8 MPa, the head generated by this pump is 190 meters (the density of LNG is 430 Kg/cubic meter). The operating parameters of this pump are as follows: flow rate range of 50–400 liters per minute, and head range of 50–280 meters. Therefore, the pump we selected is quite suitable for their needs. Their inlet diameter is DN50, but we asked them to change it to DN65. The outlet diameter of the pump itself is 32. For a flow rate of 16 cubic meters, the flow velocity in a DN65 pipe is 1.34 m/s, while it is 5.53 m/s in a DN32 pipe, and 2.26 m/s in a DN50 pipe. Thus, we asked them to use a DN32 pipe for the outlet and then reduce the diameter to DN50. However, the client raised a question that puzzled us: they said since the pump’s outlet diameter is DN32, why do we need to reduce the diameter to DN50? That implies there is a problem with the design of this pump! Our response was that it is necessary to take into account the outlet flow velocity. With a flow rate of 16 cubic meters, the flow velocity in a DN50 pipe is approximately 2.26 m/s. For LNG, we require that the maximum flow velocity not exceed 3 m/s. As for what diameters should be used for the pump’s inlet and outlet, we’re not sure either. So my question is: when designing centrifugal pumps, what criteria do pump manufacturers use to determine the diameters of the inlet and outlet pipes? As the customer mentioned: based on the pump’s flow rate and the inlet and outlet conditions, the calculated flow velocity is too high. Was the flow velocity at the inlet and outlet not taken into account during the pump’s design?
Can no one answer? There must be many designs for high-centrifugal pumps! Take it on yourself! ! !
I think you made no mistake in making that choice. The inlet and outlet pipes of the pump are one size larger than those of the pump itself, and it is normal to use reducers for connection in between. When designing a centrifugal pump, the selection of the inlet and outlet diameters takes into account several factors, including flow velocity, flow rate, net positive suction head, and output power level.
I think you made no mistake in making that choice. The inlet and outlet pipes of the pump are one size larger than those of the pump itself, and it is normal to use reducers for connection in between. When designing a centrifugal pump, the selection of the inlet and outlet diameters takes into account several factors, including flow velocity, flow rate, net positive suction head, and output power level.