First, it is necessary to select the pump type most suitable for the application, such as centrifugal pump or positive displacement pump. Assuming that you have determined that centrifugation is the most appropriate, how do you choose a suitable model to meet the required performance?
- Conditions for centrifugal pump selection:
(1) Centrifugal pump selection: physical and chemical properties of conveying medium.
The physical and chemical properties of the conveying medium directly affect the performance, material and structure of the pump, which is an important factor to be considered in the selection of centrifugal pump. The physical and chemical properties of the medium include: medium name, medium characteristics (such as corrosivity, abrasiveness, toxicity, etc.), solid particle content, particle size, density, viscosity, vaporization pressure, etc. If necessary, the gas content in the medium shall also be listed, indicating whether the medium is easy to crystallize, etc.
(2) Centrifugal pump selection: parameters.
Parameters are the most important basis for centrifugal pump selection, which should be carefully determined according to the process flow and operation variation range.
① Flow Q. Flow refers to the medium mass required to be delivered by the pump in the production of process units. Flow is also an important factor to pay attention to in the selection of centrifugal pump. Generally, the process personnel shall give the normal, minimum and maximum flow. Only normal and rated flow are often given on the pump data sheet. During the selection of centrifugal pump, the rated flow shall not be less than the maximum flow of the device, or 1.1 ~ 1.15 times of the normal flow.
② Lift H. Head refers to the head value required by the process unit, also known as calculated head. General centrifugal pump selection requires that the rated head of the pump is 1.05 ~ 1.1 times of the head required by the device.
③ Inlet pressure P and outlet pressure P. The outlet pressure refers to the pressure at the inlet and outlet connecting pipe flange of the pump. The inlet and outlet pressure affects the pressure resistance of the shell and the requirements of the shaft seal.
④ Temperature T. Temperature refers to the inlet medium temperature of the pump. Generally, the normal, minimum and maximum temperatures of the inlet medium of the pump in the process shall be given for the selection of centrifugal pump.
⑤ Npsha of the unit is also called effective npsha.
⑥ Operation status. The operation state is divided into continuous operation and intermittent operation.
(3) Centrifugal pump selection: site conditions.
The site conditions include the installation location of the pump (indoor and outdoor), ambient temperature, relative humidity, atmospheric pressure, atmospheric corrosion status, classification of hazardous areas, etc.
- Selection of materials for centrifugal pump selection:
Centrifugal pump series refers to the pumps with the same structure and purpose produced by the pump factory, such as is clean water pump, S-type double suction centrifugal pump, IH chemical pump, ZGB slurry pump, etc. Through the comparison of different materials to judge how to select the centrifugal pump. In the selection of centrifugal pump, the series and materials of the pump are selected according to the process parameters and medium characteristics.
(1) According to the characteristics of the medium, decide which characteristic pump to choose, such as clean water pump, corrosion-resistant pump and impurity pump. When the medium is highly toxic, valuable or radioactive and other substances that are not allowed to leak, consider selecting non leakage pump (such as shielded pump and magnetic pump) or double face mechanical seal with leakage liquid collection and leakage alarm device. If the medium is volatile liquid such as liquefied hydrocarbon, select low cavitation allowance pump, such as cylindrical pump.
(2) Horizontal centrifugal pump and vertical centrifugal pump (including submerged sewage pump and pipeline sewage pump) shall be selected according to the on-site installation conditions.
(3) Single stage single suction centrifugal pump, double suction centrifugal pump or small flow centrifugal pump shall be selected according to the flow of the water pump.
(4) Single stage centrifugal pump, multi-stage centrifugal pump or high-speed centrifugal pump shall be selected according to the pump head.
Finally, according to the characteristics of the device and the parameters of the pump, decide which kind of manufacturing and inspection standard to choose.