Principles and steps for pump selection: List basic data and determine flow head
1. Principles of pump selection
Water pump is a wide range of general-purpose mechanical equipment, which is widely used in petroleum, chemical, electric metallurgy, mining, ship selection, light industry, agriculture, civil and national defense departments, and it occupies an important position in the national economy. According to statistics in 1979, my country’s pump output reached 1.256 million units. The electric energy consumption of water pumps accounts for more than 21% of the national electric energy consumption. Therefore, greatly reducing the energy consumption of the pump is of great significance for energy saving.
In recent years, our water pump industry has designed and developed many high-efficiency and energy-saving products, such as QBY pumps, IHF pumps, CQB pumps, PF pumps, FSB pumps, XZ pumps, ZW pumps and other types of pump products, which have played a role in reducing pump energy consumption. positive effects. However, in various fields of the national economy, due to unreasonable model selection, many pumps are in unreasonable operating conditions, operating efficiency is low, and a lot of energy is wasted. Some pumps cannot be used at all due to unreasonable model selection, or increase in maintenance costs and low economic benefits. It can be seen that the rational selection of pumps is also of great significance to energy saving.
The so-called rational selection of pumps is to comprehensively consider the comprehensive technical and economic indicators such as the investment and operating costs of the pump unit and the pumping station, so that it conforms to the principles of economy, safety and application. Specifically, there are the following aspects:
Must meet the requirements of use flow and head, that is, the operation time point of the pump (the intersection of the device characteristic curve and the pump performance curve) must always be kept in the high-efficiency range, which saves power and is not easy to damage the parts. The selected water pump should not only be small in size, light in weight, low in cost, but also have good characteristics and high efficiency. It has good anti-cavitation performance, which can reduce the excavation depth of the pump house without causing cavitation of the water pump, so it runs smoothly and has a long life. The pumping station is built according to the selected pumps, with low project investment and low operating costs.
2. Water pump selection steps
1. The characteristics of the medium: medium name, specific gravity, viscosity, corrosiveness, toxicity, etc.
2. The particle diameter and content of the factor contained in the medium.
3. Medium temperature: (℃)
4. The required flow
Generally, industrial pumps can ignore the leakage in the piping system in the process, but the impact on the flow rate when the process changes must be considered. If agricultural pumps use open channels for water delivery, leakage and evaporation must also be considered.
5. Pressure: suction pool pressure, discharge pool pressure, pressure drop in the 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, etc.).
If necessary, the device characteristic curve should be made.
When designing and laying out piping, the following items should be noted:
A. Choose the pipe diameter reasonably. The pipe diameter is large. Under the same flow, the liquid flow speed is small, and the resistance loss is small. However, the price is high and the pipe diameter is small. With the increase of belt power, the cost and operating expenses are increased. Therefore, it should be considered from the perspective of technology and economy.
B. The discharge pipe and its pipe joints should consider the maximum pressure that it can withstand.
C. The pipeline layout should be as straight as possible, minimize the accessories in the pipeline and minimize the length of the pipeline. When it is necessary to turn, the bending radius of the elbow should be 3 to 5 times the diameter of the pipeline, and the angle should be greater than 90 as much as possible. ℃.
D. Valves (ball valves or stop valves, etc.) and check valves must be installed on the discharge side of the pump. The valve is used to adjust the working point of the pump. The check valve can prevent the pump from reversing when the liquid flows backwards and prevent the pump from being hit by water hammer. (When the liquid flows back, it will produce huge reverse pressure, which will damage the pump)
3. Determine the flow head
a. If the minimum, normal, and maximum flow rates have been given in the production process, the maximum flow rate should be considered.
b. If only the normal flow rate is given in the production process, a certain margin should be considered.
For pumps with large flow and low unintended head with ns>100, the flow margin is 5%; for small flow and high-head pumps with ns<50, the flow margin is 10%. For pumps with 50≤ns≤100, the flow margin is also Take 5%. For pumps with poor quality and poor operating conditions, the flow margin should be taken as 10%.
c. If the basic data only gives weight flow, it should be converted into volume flow.
Post time: 2021-11-30
