How to select a suitable pump
1. According to the layout of the device, terrain conditions, water level conditions, operation conditions, economic scheme comparison and other factors
2. Horizontal, vertical and other types (pipeline type, submersible type, submerged type, non blocking type and self suction type) shall be considered.
3. According to the properties of the liquid medium, determine the water pump, hot water pump, oil pump, chemical water pump or corrosion-resistant water pump or impurity water pump, or use the non blocking water pump.
4. The water pump installed in the explosion area shall adopt explosion-proof motor according to the grade of explosion area.
5. Vibration is divided into: pneumatic, electric (electric divided into 220 V voltage and 380 V voltage).
6. According to the flow size, choose single suction pump or double suction pump: according to the head, choose single suction pump or multi suction pump, high speed water pump or low speed water pump (air conditioning water pump), and the efficiency of multi-stage water pump is lower than that of single-stage water pump. When single-stage water pump and multi-stage water pump are selected, single-stage pump should be selected.
7. After determining the specific model of the water pump and which series of pumps are selected, the specific model can be determined on the series characteristic curve or the most suitable pump can be selected by the selection software according to the maximum flow and the two main performance parameters of 5% - 10% margin.
Use the pump characteristic curve to find the required flow value on the abscissa and the required lift value on the ordinate. Draw a vertical line or a horizontal line from the two values respectively, and the intersection point of the two lines just falls on the characteristic curve, then the pump is the pump to be selected. However, this ideal situation is not rare, and usually meets 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 head difference is not much, or the difference is about 5%, it can still be selected. If the head difference is large, select the pump with larger head, or try to reduce the pipeline resistance loss.
B. The second kind: the intersection point is under the characteristic curve, within the fan-shaped trapezoid range of the pump characteristic curve This model is initially determined, and then the impeller diameter is determined according to the difference of head. If the head difference is very small, the impeller diameter is not cut. If the head difference is very large, the impeller diameter is cut according to the required Q, h, NS and cutting formula. If the intersection point does not fall within the fan-shaped trapezoid range, the pump with smaller head should be selected.
When selecting pumps, it is necessary to consider the production process requirements and select different shapes of Q-H characteristic curves. For example: to transport the liquid level to the container which must maintain a certain liquid level height, at this time, the variable hope quantity has a big change, but the head change is very small, so the flat H-O curve pump should be selected.
For example: the oil is sent to the tubular heating furnace. If the flow rate changes little during the operation, the furnace tube is easy to produce coking phenomenon. In order to avoid this situation, it is hoped that when the flow rate is slightly reduced, the oil pressure in the pipe will increase greatly, so that the coke scar just formed will be washed away by the higher liquid flow pressure. At this time, the oil-water pump with relatively low Q-H curve should be selected.
7. After the water pump model is determined, the water pump or the water pump whose physical and chemical medium of conveying medium is close to water shall be added to the relevant product catalog or sample, and the correction shall be carried out according to the performance table or performance curve of the model to see whether the normal working point falls in the priority working area of the pump, and whether the effective NPSH is greater than (NPSH). In turn, NPSH can be used to correct the geometric installation height?
8. For the liquid pump with the delivery viscosity greater than 20mm2 / s, it is necessary to convert the characteristic curve of the water test pump into the performance curve of the viscosity, especially to carefully calculate or check the suction performance.
9. Determine the number of pumps and reserve rate
For the normal operation of the pump, generally only one pump, because a large pump and parallel work of two small pumps (the same head, flow), the efficiency of the large pump is higher than that of the small pump, so from the perspective of energy saving, it is better to choose a large water pump instead of two small pumps, but in case of the following situations, we can consider the parallel cooperation of two water pumps: the flow is large, and one pump can not reach This traffic.