When designing the equipment, the design institute must determine the purpose and performance of the pump and select the type of disintegration. This choice starts with choosing the type and form of the pump. Then what principle does the pump choose? What is the basis?

First, understand the selection principle of the pump

1. Make the type and performance of the selected pump meet the requirements of process parameters such as flow rate, head, pressure, temperature, cavitation flow, and suction stroke.

2, must meet the requirements of the media characteristics.

For pumps that emit flammable, explosive toxic or valuable media, shaft seals are required or leak-free pumps are used. For example, magnetic drive pumps, diaphragm pumps, and shielded pumps are used to pump corrosive media. Corrosion resistant materials are required for convection parts. , Such as AFB stainless steel anti-corrosion pump, CQF engineering plastic magnetic drive pump.

For the pump containing solid particles, it is required that the convection part be made of wear-resistant material, and if necessary, the shaft seal should be cleaned with a clean liquid.

3, mechanical reliability, low noise, vibration.

4. Economically, the total cost of equipment, operating costs, maintenance and management fees should be taken into account in a comprehensive manner.

5. Centrifugal pumps have features such as high speed, small size, light weight, high efficiency, large flow rate, simple structure, no pulse infusion, stable performance, easy operation and convenient maintenance.

Therefore, centrifugal pumps should be used as much as possible except in the following cases:

a、When there are measurement requirements, choose the metering pump b, the lift head is high, the flow is very small and there is no suitable small flow High-lift centrifugal pump can be used, the reciprocating pump can be used, if the cavitation requirements are not high, the vortex pump can also be used .

c. When the lift is very low and the flow rate is large, axial and mixed flow pumps can be used.

d. When the viscosity of the medium is larger (greater than 650~1000mm2/s), the rotor pump or reciprocating pump (gear pump, screw pump) may be considered.

e. The vortex pump can be used when the medium gas content is 75%, the flow is small and the viscosity is less than 37.4mm2/s.

f. For occasions with frequent startup or inconvenient pumping, pumps with self-priming properties should be used, such as self-priming centrifugal pumps, self-priming vortex pumps, and pneumatic (electric) diaphragm pumps.

Second, know the basic basis of pump selection

Pump selection basis, should be based on the process flow, water supply and drainage requirements, from five aspects to be considered, both liquid delivery volume, device lift, liquid properties, piping layout and operating conditions.

1. Flow rate is one of the important performance data for pump selection. It is directly related to the production capacity and conveying capacity of the entire device. For example, in the process design of the design institute, the normal, minimum and maximum flow rates of the pump can be calculated. When the pump is selected, the maximum flow rate is taken as the basis and the normal flow rate is taken into consideration. When there is no maximum flow rate, it is usually possible to take 1.1 times of the normal flow rate as the maximum flow rate.

2. The required lift of the device system is another important performance data of the pump selection. Generally, it is necessary to select the head after amplification with 5%-10% margin.

3, liquid properties, including the liquid medium name, physical properties, chemical properties and other properties, physical properties of the temperature c density d, viscosity u, the diameter of the solid particles in the medium and the gas content, which involves the system's lift, effective gas Corrosion margin calculation and the type of suitable pump: chemical properties, mainly referring to the chemical corrosivity and toxicity of the liquid medium, is an important basis for choosing the pump material and the type of shaft seal.

4. The pipeline layout conditions of the installation system refer to the liquid-feeding distance of the liquid-feeding distance, the suction of the minimum liquid level, the maximum liquid level of the discharge side, and some data and pipe specifications, and their lengths, materials, and pipe fittings specifications. Etc. for the check of the combing head calculations and the NPSH margin.

5, the operating conditions of many content, such as liquid operation T saturated steam force P, suction side pressure PS (absolute), discharge side container pressure PZ, altitude, ambient temperature operation is a gap or continuous, the pump position is fixed It's still removable.

Third, the specific operation of the pump

According to pump selection principle and basic conditions for selection, the specific operation is as follows:

1, according to the device layout, terrain conditions, water level conditions, operating conditions, determine the choice of horizontal, vertical and other types (pipeline, submersible, submerged, non-blocking, self-priming, gear, etc.) Pump.

2, according to the nature of the liquid medium, determine the clean water pump, hot water pump or oil pump, chemical pump or corrosion-resistant pump or impurity pump, or use non-clogging pump.

Pumps installed in explosive areas should be equipped with explosion-proof motors according to the level of the explosion zone.

3, according to the flow size, determine the menu suction pump or double suction pump; according to the level of lift, single-stage pump or multi-stage pump, high-speed pump or low-speed pump (air-conditioning pump), multi-stage pump efficiency lower than single-stage pump, such as When a single-stage pump and a multi-stage pump can be used, the single-stage pump is used first.

4, determine the specific model of the pump to determine the use of what series of pumps, you can press the maximum flow, (in the absence of maximum flow, you can usually take the normal flow of 1.1 times as the maximum flow), take 5% -10% after amplification The head of these two main parameters of the performance, in the spectrum or series of characteristics to determine the specific model. The operation is as follows:

Using the pump characteristic curve, find the desired flow value on the abscissa and find the required head value on the ordinate, and draw the vertical or horizontal line from the two values ​​up and to the right. The intersection of the two lines falls exactly on the characteristic curve. The pump is the pump to be selected, but this ideal situation is generally very small, usually encounter the following two conditions:

The first kind: the intersection point is above the characteristic curve. This shows that the flow rate meets the requirements, but the lift is not enough. At this time, if the heads are almost the same, or the difference is about 5%, they can still be used. If there is a lot of difference in the lift, the pump with a larger lift is selected. . Or try to reduce pipeline resistance loss.

The second type: the intersection point is below the characteristic curve. Within the range of the fan-shaped trapezoid of the pump characteristic curve, this model is preliminarily set, and then according to how much the head difference, to decide whether to cut the impeller diameter, if the head difference is very small, it will not be cut. The heads are quite different. According to their ns and cutting formulas, the diameter of the impeller is cut. If the intersection does not fall within the range of the fan-shaped trapezoid, the pump with a smaller lift should be selected. When selecting a pump, sometimes the production process requirements must be taken into account, and different QH characteristic curves should be selected.

5, after the pump model is determined, the pump of the physical and chemical medium similar to the water pump or the transmission medium, need to go to the relevant product catalog or sample, according to the model performance table or performance curve correction, to see whether the normal working point falls in the Pump priority work area? Whether the effective NPSH is greater than (NPSH). Can also be reversed to NPSH correction geometry installation height?

6, for the delivery of liquid viscosity greater than 20mm2 / s liquid pump (or density greater than 1000kg/m3), must be the water test pump characteristic curve is converted to the viscosity (or the density) of the performance curve, especially for the suction performance and The input power is carefully calculated or compared.

7, determine the number of pumps and standby rate:

Normally only one pump is used for normal operation, because one large pump is equivalent to two small pumps working in parallel (refers to the head and the same flow rate). The efficiency of the large pump is higher than that of the small pump. Taiwan Tai pump, instead of two small pumps, but in the following cases, consider two pumps in parallel:

The flow rate is very high and one pump cannot reach this flow.

For large pumps that require a 50% standby rate, two smaller pumps can be changed and two spares (three in total)

For some large pumps, a 70% flow rate pump can be used in parallel to operate without a backup pump. When one pump is inspected, the other pump still takes 70% of the production.

For pumps that require 24 hours of continuous operation, spare three pumps, one for operation, one for standby, and one for maintenance.

8. Under normal circumstances, customers can submit their "selection of the basic conditions of the pump". Our company will give a selection or recommend a better pump product. If the design institute is designing equipment, the model of the pump has been determined and it is configured according to the requirements of the design institute.

9, determine the number of pumps and standby rate:

Normally only one pump is used for normal operation, because one large pump is equivalent to two small pumps working in parallel (refers to the head and the same flow rate). The efficiency of the large pump is higher than that of the small pump. Taiwan Tai pump, instead of two small pumps, but in the following cases, consider two pumps in parallel:

The flow rate is very high and one pump cannot reach this flow.

For large pumps that require a 50% standby rate, two smaller pumps can be changed and two spares (three lifts in total)

For some large pumps, a 70% flow rate pump can be used in parallel to operate without a backup pump. When one pump is inspected, the other lift pump still takes 70% of the production.

For pumps that require 24 hours of continuous operation, three pumps should be spared for operation, one for standby and one for maintenance.