Pump selection requirements
Date of issue:[2020-08-17] Click through rate:Section 1 selection principles
Pump is a kind of general-purpose mechanical equipment, which is widely used in petroleum, chemical industry, electric power metallurgy, mining, ship selection, light industry, agriculture, civil and national defense departments, and occupies an important position in the national economy. According to statistics in 1979, the output of pumps in China reached 1.256 million units. The electric energy consumption of pumps accounts for more than 21% of the national electric energy consumption. Therefore, it is of great significance to reduce the energy consumption of pumps to save energy.
In recent years, our pump industry has designed and developed many high-efficiency and energy-saving products, such as IHF, CQB, FSB, uhB and other types of pump products, which has played a positive role in reducing the energy consumption of pumps. However, in various fields of the national economy, due to the unreasonable selection of the pump, many pumps are in unreasonable operation, low operation efficiency and waste a lot of energy. Some pumps can not be used because of unreasonable selection, or the maintenance cost is increased and the economic benefit is low. Therefore, reasonable pump selection is of great significance to energy saving.
The so-called reasonable pump selection is to comprehensively consider the investment and operation cost of pump units and pump stations and other comprehensive technical and economic indicators, so as to make them conform to the principles of economy, safety and applicability. Specifically, there are the following aspects:
1. It is necessary to meet the requirements of flow rate and head, that is to say, the operation time point (the intersection point of the device characteristic curve and the pump performance curve) of the pump should always be kept in the high efficiency range, so as to save power and not to damage the parts.
2. The selected pump should not only be small in size, light in weight and cheap in cost, but also have good characteristics and high efficiency.
3. It has good anti cavitation performance, which can not only reduce the excavation depth of the pump house, but also prevent the pump from cavitation, so that the operation is stable and the service life is long.
4. According to the selected pump station, the project investment is less and the operation cost is low.
Section 2 selection steps
1、 List basic data:
1. Characteristics of medium: medium name, specific gravity, viscosity, corrosivity, toxicity, etc.
2. The particle diameter and content of the factor in the medium are determined.
3. Medium temperature: (℃)
4. Required traffic
The leakage in pipeline system can be ignored in general industrial pump process, but the influence of process change on flow must be considered. If the agricultural pump is to use open channel water delivery, leakage and evaporation must also be considered.
5. Pressure: suction tank pressure, drainage tank pressure, pressure drop in piping system (head loss).
6. Piping system data (pipe diameter, length, type and number of pipe accessories, geometric elevation from suction tank to pressure tank).
If necessary, the device characteristic curve should also be drawn.
In the design and layout of pipelines, attention should be paid to the following matters:
A. Reasonable selection of pipe diameter, large pipe diameter, under the same flow rate, liquid flow speed is small, resistance loss is small, but high price, small pipe diameter, will lead to a sharp increase in resistance loss, increase the head of the selected pump, increase the power of the matching, and increase the cost and operating costs. Therefore, it should be considered comprehensively from the angle of technology and economy.
B. The maximum pressure that the discharge pipe and its joint can bear shall be considered.
C. The pipeline layout should be as straight as possible, the accessories in the pipeline and the length of the pipe should be reduced as far as possible. When turning is necessary, the bending radius of the elbow should be 3-5 times of the pipe diameter, and the angle should be greater than 90 ℃.
D. The discharge side of the pump must be equipped with valves (ball valve or globe valve, etc.) and check valve. The valve is used to adjust the operating point of the pump. The check valve can prevent the pump from reversing when the liquid flows backward, and make the pump avoid the impact of water hammer. (when the liquid flows backward, a huge reverse pressure will be generated, which will damage the pump)
2、 Determine flow head
1. Determination of flow rate
a. If the minimum, normal and maximum flow rates have been given in the production process, the maximum flow rates should be considered.
b. If only normal flow rate is given in the production process, some allowance should be considered.
For large flow and low head pumps with NS > 100, the flow margin should be 5%; for the small flow high lift pump with NS < 50, the flow margin should be 10%; for the pump with 50 ≤ ns ≤ 100, the flow margin should also be 5%; for the pump with poor quality and poor operating conditions, the flow margin should be taken as 10%.
c. If the basic data only gives the weight flow rate, it should be converted into volume flow rate.
This paper is reprinted from: complete knowledge of water pump in China
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