Single-stage centrifugal pump, multi-stage centrifugal pump selection steps
According to the principle of pump selection and the basic conditions of selection data, the specific selection steps of single-stage centrifugal pump and multi-stage centrifugal pump are as follows:
Multistage centrifugal pump
1. According to the arrangement of the device, terrain conditions, water level conditions, and operating conditions, determine the choice of horizontal, vertical and other types (pipeline, submersible, submerged, non-clogging, self-priming, gear, etc.)
2. Determine the clean water pump, hot water pump, oil pump, chemical pump or corrosion-resistant pump or impurity pump according to the nature of the liquid medium, or use a non-clogging pump. The pump installed in the explosion area should adopt the corresponding explosion-proof motor according to the explosion area grade.
3. According to the flow rate, determine whether to select a single suction pump or a double suction pump. According to the head level, choose single-stage pump or multi-stage pump, high-speed pump or low-speed pump (air conditioning pump). The efficiency of multi-stage pumps is lower than that of single-stage pumps. If single-stage pumps and multi-stage pumps can be used as well, single-stage pumps should be selected first.
4. Determine the specification, model and structure of the pump
(1) After determining what series of pumps to choose, you can press the maximum flow rate (when there is no maximum flow rate, usually 1.1 times the normal flow rate can be taken as the maximum flow rate), and take the two heads after magnifying 5% and 10% of the margin The main parameters of performance, the specific model is determined on the type spectrum or series characteristic curve.
(2) Using the pump characteristic curve, find the required flow value on the abscissa and the required head value on the ordinate, draw a vertical or horizontal line from the two values up and to the right, and the intersection of the two lines just falls on the characteristic curve , The pump is the pump to be selected. However, 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 the same, or the difference is about 5%, it can still be used. If the head difference is much, choose the larger head Pump. Or try to reduce the pipeline resistance loss.
The second type: The intersection point is below the characteristic curve and within the fan-shaped trapezoid range of the pump characteristic curve. This model is preliminarily determined, and then according to the difference in the head, it is decided whether to cut the impeller diameter. If the difference in the head is very small, it will not be cut. If there is a big difference in head, cut the impeller diameter according to the required Q, H, ns and cutting formula. If the intersection does not fall within the fan-shaped trapezoid, a pump with a smaller head should be selected. When selecting a pump, sometimes it is necessary to consider the requirements of the production process and select different shapes of QH characteristic curves.
7. The structure of the shaft seal:
According to the characteristics of the conveyed medium, the appropriate shaft seal structure should be designed and selected.
8. Material selection: selection of non-metallic materials for the pump
Pump's non-metallic material selection table
8. Determine the number of pumps and reserve rate:
①. Generally, only one pump is used for normal operation. 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 save energy Choose one big pump instead of two small pumps.
But in case of special circumstances, the flow rate is very large, and one pump cannot reach this flow rate, so two pumps can be considered for combined use
②. For large pumps that require a 50% standby rate, two smaller pumps can be changed to work, and one standby (three in total);
③. For some large pumps, 70% of the pumps with flow requirements can be used in parallel. No spare pumps are needed. When one pump is overhauled, the other pump still bears 70% of the production.
④. 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
9. Under normal circumstances, customers can submit their "basic conditions for pump selection", and the manufacturer will select the model or recommend a better pump product. If the design institute has determined the pump model when designing the installation equipment, configure it according to the requirements of the design institute.
10、Pump selection data sheet
(1) The performance specification table provided by the manufacturer
(2) Working condition data sheet provided by the design institute
(3) Material data sheet provided by the design institute
(4) Work environment data sheet provided by the design institute.
