Section 1: Selection principle
Pump is a kind of general purpose mechanical equipment with a wide range of application. It is widely used in petroleum, chemical industry, electric power metallurgy, mining, ship selection, light industry, agriculture, and civil and national defense departments and occupies an important position in the national economy. In 79 years, we have 1256 million pumps. The power consumption of the pumps is over 21% of the national power consumption. It is significant to reduce that energy consumption of the pump.
At present, in various fields of the national economy, due to the unreasonable selection, many pumps are in an unreasonable operating condition, operating efficiency is low, and a lot of energy is wasted. Some pumps can not be used at all due to unreasonable type selection, or the use of maintenance costs, low economic benefits. It can be seen that reasonable selection of pump energy saving is also of great significance.
The so-called rational choice pump which is to take into account the investment and operating expenses of the pump station and so on, to meet the economic, safe, and applicable principles of the economy. Specifically, there are the following aspects:
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1. The requirements of flow rate and head must be met. That is, the operating condition point of the pump (the point of intersection of the characteristic curve of the device and the performance curve of the pump) is often maintained in the high-efficiency section so as to both save power and not damage the machine 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 cavitations resistance performance, which can not only reduce the excavation depth of the pump room, but also avoid cavitations of the pump, so that the operation is smooth and the service life is long.
4. The pump selected to build a pump station, the project investment is low, low operating costs.
Section 2: selection steps
一 list basic data:
1. Properties of medium: medium name, specific gravity, viscosity, corrosion, toxicity, etc.
2. The diameter and content of solid particles contained in the medium.
3. The medium temperature (℃)
4. Required flow rate
General industrial pumps in the process flow can ignore the amount of leakage in the pipeline system, but must consider the impact of process changes on the flow rate. Agricultural pumps must also take into account leakage and evaporation if water is to be transported by open channels.
5. Pressure: suction tank pressure, drain tank pressure, pressure drop in pipeline system (head loss).
6. Pipeline system data (pipe diameter, length, type and number of pipe accessories, geometric elevation from suction tank to pressure tank, etc.)
Device characteristic curves should be drawn if necessary.
When designing and arranging pipelines, attention should be paid to the following matters:
A. Reasonable selection of pipe diameter, large pipe diameter, at the same flow rate, the liquid flow speed is small, the resistance loss is small, but the price is high, the pipe diameter is small, will lead to A sharp increase in resistance loss, so as to increase the head of the selected pump, with increased power, costs and operating costs. Therefore, it should be considered comprehensively from the perspective of technology and economy.
B. The discharge pipe and its joints shall take into account the maximum pressure they can bear.
C. Pipeline layout should decorate straight pipe as far as possible, try to reduce the attachment and try to narrow the pipe length, pipe must turn, elbow bend radius should be 3 ~ 5 times the diameter of the pipe, as much as possible Angle is greater than 90 ℃.
D. The discharge side of the pump must be equipped with valves (ball valves or globe valves, etc.) and check valves. The valve is used to adjust the working point of the pump. The reverse check valve can prevent the pump from reversing when the liquid flows back, and make the pump avoid the impact of water hammer. (when the liquid flows back, it will generate huge reverse pressure, causing damage to the pump)
二 Determine the flow rate and head
Determination of flow rate
A. If the minimum, normal and maximum flow rates have been given in the production process, the maximum flow rate shall be considered.
B. If only the normal flow rate is given in the production process, a certain amount of allowance should be considered.
For ns>100 high-flow low-lift pump, the flow margin is 5%. For ns<50 small flow high head pump, the flow margin is 10%.For pumps with 50 or less than ns or less than 100, the flow margin is also taken as 5%, for pumps with inferior quality and poor operating conditions, the flow margin shall be 10%.
C. If the basic data only give weight flow, it should be converted into volume flow.
