May 31, 2021
1. According to the layout of the device, topographical conditions, water level conditions, operating conditions, comparison of economic plans, etc.
2. Consider choosing horizontal, vertical and other types (pipe, right-angle, variable angle, corner, parallel, vertical, vertical, submersible, easy-to-remove, submerged, non-blocking, Self-priming, gear, oil-filled, water-filled temperature).
Horizontal pumps are easy to assemble and disassemble, and easy to manage, but they are bulky, expensive, and require a large area;
Vertical pumps, in many cases, the impeller is submerged in water, which can be started at any time, which is convenient for automatic pumping or remote control. It is compact, has a small installation area, and is cheaper.
3. According to the nature of the liquid medium, determine the clean water pump, hot water pump, oil pump, chemical pump or corrosion-resistant pump or impurity pump, or use non-blocking pump.
Pumps installed in explosion areas shall use explosion-proof motors in accordance with the explosion area rating.
4. The amount of vibration is divided into: pneumatic, electric (electric is divided into 220v voltage and 380v voltage).
5. Select single-suction pump or double-suction pump according to the flow rate: select single-suction pump or multi-suction pump, high-speed pump or low-speed pump (air-conditioning pump), and multi-stage pump is less efficient than single-stage pump, depending on the head. When both stage and multistage pumps can be used, single stage pumps should be used.
6. Determine the specific model of the pump. After selecting the series of pumps, you can enlarge the two main performance parameters of the lift after 5%-10% of the remaining head according to the maximum flow rate. Determine the specific model.
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 the vertical or horizontal line up and to the right, respectively. The intersection of the two lines just falls on the characteristic curve. This pump is the pump to choose, but this ideal situation is generally not small, and usually encounters the following situations:
A. The first type: the intersection point is above the characteristic curve, which indicates 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 head is selected to be larger. Pump. Or try to reduce the pipeline resistance loss.
B. The second type: the intersection point is below the characteristic curve, and within the fan trapezoidal range of the pump characteristic curve, this model is initially determined, and then the impeller diameter is cut according to the head difference. If the head difference is small, the cutting is not performed. If the heads are very different, cut the impeller diameter according to the required Q, H, according to its ns and cutting formula. If the intersection point does not fall within the fan-shaped trapezoidal range, a pump with a smaller head should be selected. When selecting a pump, sometimes it is necessary to consider the production process requirements and select different shapes of Q-H characteristic curves.
For example, when the liquid level is to be transported to a container that must maintain a certain level of liquid level, the flow rate will have a large change, and the head change will be small. Therefore, a pump with a flat H-O curve should be used for this purpose.
For example, if oil is sent to a tube heating furnace, if the flow change during work is small, coking will easily occur in the furnace tube. To avoid this situation, when the flow rate is slightly reduced, the pressure of the oil in the pipe is greatly increased, so that the scars that are to be formed are washed away by the higher fluid pressure. At this time, an oil pump with a Q-H curve with a relatively low drop should be used.
7. After the model of the pump is determined, the pump that is similar to water in the physical and chemical medium of the pump or transport medium needs to go to the relevant product catalog or sample, and check according to the model's performance table or performance curve to see if the normal operating point falls within the range. Pump priority work area? Whether the effective NPSH is greater than (NPSH). Can the geometry installation height be calibrated in reverse with NPSH?
8. For liquid pumps with a viscosity greater than 20mm2 / s, the characteristic curve of the water experimental pump must be converted into the performance curve of the viscosity, and the suction performance must be carefully calculated or compared.
9. Determine the number of pumps and standby rate:
Normally, only one pump is used, because a large pump is equivalent to two small pumps working in parallel (referring to the same head and flow), 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 pump instead of two small pumps, but in the following situations, you can consider two pumps in parallel cooperation: a large flow, one pump can not reach this flow.
For large pumps that require a 50% standby rate, two smaller pumps can be changed to work. For two large pumps (a total of three), for some large pumps, a 70% flow rate pump can be used in parallel instead of the standby pump. When one pump is overhauled, the other pump is still responsible for 70% of the production. For pumps that need to run continuously for 24 hours, three pumps should be backed up, one running, and one for maintenance.