According to the pump selection principle and basic conditions of selection, the specific operations are as follows:
1. According to the arrangement of the device, terrain conditions, water level conditions, and operating conditions, determine the selection of horizontal, vertical and other types of pumps (pipeline, submersible, submerged, non-blocking, self-priming, gear, etc.).
2. According to the nature of the liquid medium, determine the clean water pump, hot water pump or oil pump, chemical pump or corrosion-resistant pump or impurity pump, or use a non-clogging pump. The pump installed in the explosion area should use the corresponding explosion-proof motor according to the level of the explosion area.
3. According to the flow rate, determine whether to choose a single-suction pump or a double-suction pump; according to the height of the lift, choose a single-stage pump or a multi-stage pump, a high-speed pump or a low-speed pump (air conditioning pump), and the efficiency of a multi-stage pump is lower than that of a single-stage pump, such as a single-stage pump. When both pumps and multi-stage pumps can be used, single-stage pumps are used first.
4. Determine the specific model of the pump
After determining what series of pumps to choose, the maximum flow rate can be used (when there is no maximum flow rate, 1.1 times the normal flow rate can be usually taken as the maximum flow rate), and the lift after enlarging the head by 5%-10% margin can be taken as the difference between the two performances. The main parameters, determine the specific model on the type spectrum or series characteristic curve. The operation is as follows:
Using the pump characteristic curve, find the required flow value on the abscissa and the required head value on the ordinate, and draw a vertical line or a horizontal line from the two values upward and to the right respectively, and the intersection of the two lines falls on the characteristic curve, then This pump is the pump to be selected, but this ideal situation is generally rare, and the following two situations are usually encountered:
The first type: the intersection point is above the characteristic curve, which means that the flow meets the requirements, but the head is not enough. At this time, if the head is similar, or the difference is about 5%, it can still be used. If the head is very different, choose a pump with a larger head. . Or try to reduce the loss of pipeline resistance.
The second type: the intersection point is below the characteristic curve, within the fan-shaped trapezoid range of the pump characteristic curve, the model is initially determined, and then according to the difference in lift, it is decided whether to cut the diameter of the impeller.
If the head difference is very small, do not cut it. If the head difference is very large, cut the impeller diameter according to the required Q, H, and according to its ns and cutting formula. small pump. When choosing a pump, sometimes it is necessary to consider the production process requirements, and choose Q-H characteristic curves of different shapes.
5. After the pump model is determined, for the pump or the pump whose physical and chemical medium is similar to water, it is necessary to go to the relevant product catalog or sample, and correct it according to the performance table or performance curve of the model to see whether the normal operating point falls on the pump priority. work area? Whether the effective NPSH is greater than (NPSH). Can it be reversed to correct the geometric installation height with NPSH?
6. For liquid pumps with a viscosity greater than 20mm2/s (or a density greater than 1000kg/m3), it is necessary to convert the characteristic curve of the water experimental pump into the performance curve of the viscosity (or under the density), especially the suction performance and input power. Do serious calculations or comparisons.
7. Determine the number of pumps and spare rate:
a. Generally, only one pump is used for normal operation, because one large pump is equivalent to two small pumps working in parallel (meaning the same lift and flow), the efficiency of the large pump is higher than that of the small pump, so from the perspective of energy saving, it is preferable to Choose a large pump instead of two small pumps, but in the following situations, consider the parallel cooperation of two pumps: the flow rate is very large, and one pump cannot reach this flow rate.
b. For large pumps that need a 50% standby rate, two smaller pumps can be changed to work, one for standby (three in total).
c. For some large pumps, pumps with 70% flow requirements can be selected for parallel operation, and no spare pump is needed. When one pump is overhauled, the other pump still undertakes 70% of the transportation in production.
d. For pumps that need to run continuously for 24 hours, three pumps should be spared, one for operation, one for standby and one for maintenance.
8. Under normal circumstances, customers can submit their “Basic Conditions for Pump Selection”, and our company will select models or recommend better pump products. If the design institute has determined the model of the pump when designing the equipment, configure it according to the requirements of the design institute.
