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General procedure for water pump selection

General procedure for water pump selection

2020-06-29

Many people have questions: how to choose a suitable water pump? In this article, I will share you how to choose it in ten situations.


1. According to various factors such as device layout, terrain conditions, water level conditions, operating conditions, and comparison of economic schemes, etc.


2. Consider choosing horizontal, vertical and other types (pipeline, right angle, variable angle, corner, parallel, vertical, vertical, vertical, submersible, detachable, submerged, non-clogging, Self-priming, gear, oil-filled, water-filled temperature type).


3. According to the nature of the liquid medium, determine the clean water pump, hot water pump, oil pump, chemical pump, corrosion-resistant pump or impurity pump, or use a non-clogging pump.


4. The water pump installed in the explosion area should use explosion-proof motor according to the explosion area grade.


5. The amount of vibration is divided into: pneumatic and electric (electric is divided into 220v voltage and 380v voltage).


6. According to the flow rate, whether the single suction pump or the double suction pump is selected: according to the height of the head, whether the single suction pump is a multiple suction pump, the high-speed pump or the low-speed pump (air conditioning pump), the efficiency of the multi-stage pump is lower than that of the single-stage pump, and is selected. When both the multi-stage pump and the multi-stage pump can be used, the single-stage pump should be used.


7. Determine the specific model of the water pump. After selecting the series of water pumps, you can enlarge the two main performance parameters of the head after the 5%-10% margin according to the maximum flow, and determine the specific model on the series characteristic curve. Or use the selection software to select the most suitable pump (the following figure intercepts the definition dimension selection software).


Use the pump characteristic curve to find the required flow value on the abscissa and the required head value on the ordinate. From the two values, draw a vertical line or a horizontal line up and to the right. The intersection of the two lines falls on the characteristic curve, then The water pump is the water pump to be selected, but this ideal situation is generally not rare, and usually encounters the following situations:


A. The first kind: the intersection point is above the characteristic curve, which shows that the flow meets the requirements, but the head is not enough. At this time, if the heads are similar, or the difference is about 5%, it can still be used. If the heads are very different, the larger head is selected. Pump, or try to reduce the pipeline resistance loss (the following figure intercepts the definition dimension selection software).


B. The second type: the intersection point is below the characteristic curve, within the fan-shaped trapezoidal range of the pump characteristic curve, this model is initially determined, and then whether to cut the diameter of the impeller is determined according to how much the head difference is. If the head difference is small, it will not be cut. If the difference in head is large, according to the required Q, H, according to its ns and cutting formula, cut the diameter of the impeller. If the intersection point does not fall within the range of the fan-shaped trapezoid, the pump with a smaller head should be selected. Selection software).


When selecting a water pump, sometimes it is necessary to consider the production process requirements and select Q-H characteristic curves of different shapes. For example, to transfer the liquid level to a container that must maintain a certain liquid level, there is a large change in the desired amount at this time, and the head change is very small. For this time, a flat H-O curve pump should be used.


It is like: sending oil to the tube heating furnace, if the flow rate changes in the work is small, coking phenomenon will easily occur in the furnace tube. To avoid this situation, it is hoped that when the flow rate is slightly reduced, the pressure of the oil in the pipe will be greatly increased, so that the scorch scar just formed will be washed away by the higher fluid pressure. At this time, the QH curve should be used more Oil water pump.


8. After the model of the pump is determined, for the water pump or the pump whose physical and chemical medium is similar to water, you need to go to the relevant product catalog or sample and make corrections according to the model performance table or performance curve to see if the normal operating point falls What is the priority working area of the pump? Whether the effective NPSH is greater than (NPSH). Can the geometry installation height be reversed with NPSH?


9. For liquid pumps with a viscosity greater than 20mm2/s, the characteristic curve of the water test pump must be converted into the performance curve of the viscosity, especially the suction performance should be carefully calculated or compared.


10. Determine the number and standby rate of pumps

Normally, only one pump is used, because a large pump is equivalent to two small pumps working in parallel (refer to the same head and flow rate), the efficiency of the large pump is higher than that of the small pump, so it is better to choose one from the perspective of energy saving Large pumps are used instead of two small pumps, but in the following situations, two pumps can be considered to work in parallel: the flow is very large, and one pump cannot reach this flow.


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