When designing a pump regarding its inlet and outlet diameters, what size should these diameters be? What is the basis?
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Technical data for several pumps produced by our company: (LNG stands for liquefied natural gas; its density is 430 Kg/cubic meter, and its temperature is -162°C.) The LNG centrifugal pump (SGM 185) has a flow rate of 85–910 l/min and a head of 110–410 m. The inlet and outlet diameters are DN65 and DN40 respectively. When the flow rate is 20 cubic meters per hour (333 l/min), the inlet velocity is 1.68 m/s, while the outlet velocity is 4.42 m/s. The LNG submersible pump (ARTIKA 2S) has a flow rate of 50–400 l/min and a head of 50–280 m; its inlet and outlet diameters are DN65 and DN32 respectively. At a flow rate of 15 cubic meters per hour (250 l/min), the inlet velocity is 1.26 m/s, and the outlet velocity is 5.31 m/s. The LNG centrifugal pump has dimensions of 1.5″×2.5″×6″ (outlet diameter×inlet diameter×impeller diameter); its maximum flow rate can reach 567.8 l/min, with a head of up to 300 m. Again, at a flow rate of 20 cubic meters per hour (333 l/min), the inlet velocity is 1.68 m/s, and the outlet velocity is 4.42 m/s. Based on these figures, if the outlet diameters of these centrifugal pumps remain unchanged, the velocity would exceed the maximum allowable value for LNG, which is 3 m/s. Therefore, I would like to ask: 1. What is the basis for pump manufacturers when selecting the diameters of the pump’s inlet and outlet? Why choose such a large size? 2. When designing a pump, do designers not consider the flow velocities at the pump’s inlet and outlet?
The design of the pump’s outlet pipe diameter usually takes energy recovery into account; therefore, it is generally made relatively small. The person asking the question should not use the requirements regarding flow velocity in the pipeline to restrict the pump. The problem can be solved by using reducers to increase the diameter of the pump’s outlet pipeline.
Reply to 2# bage: Could you be more detailed? We always need to give the customer an explanation!
Bage said it well; it suddenly became clear.
When pumps leave the factory, the diameter of the inlet and outlet pipes for any given model is fixed. As for connecting them to pipelines, the pipe diameter can be adjusted using reducers. For example, our product 1*2*6 MODEL:C-C has an inlet diameter of 2 inches, an outlet diameter of 1 inch, and an impeller diameter of 6 inches; these values are fixed and cannot be changed. As long as this model meets the requirements regarding flow rate and pressure, it is suitable for use