Principle and basis of pump selection

Selection principle

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

The requirements for the properties of the medium must be met.
For pumps that transport flammable, explosive, toxic, or precious media, reliable shaft seals or leak-free pumps are required, such as magnetic drive pumps, diaphragm pumps, and canned pumps
For pumps that transport corrosive media, corrosion-resistant materials are required for convection components.
For pumps that transport media containing solid particles, wear-resistant materials are required for convection parts, and shaft seals are flushed with clean liquid if necessary.

Mechanically, it has high reliability, low noise, and low vibration.

Economically, the total cost of equipment cost, operation cost, maintenance cost, and management cost should be considered to be the lowest.

The centrifugal pump has the characteristics of high speed, small volume, light weight, high efficiency, large flow, simple structure, no pulsation of infusion, stable performance, easy operation, and convenient maintenance.
Therefore, except for the following situations, centrifugal pumps should be used as far as possible:
a. When there is a metering requirement, use a metering pump.
b. When the lift requirement is very high, the flow rate is small and there is no suitable small flow and high lift centrifugal pump, the reciprocating pump can be selected, and the vortex pump can also be selected when the cavitation requirement is not high.
c. When the lift is very low and the flow is large, axial flow pump and mixed flow pump can be selected.
d. When the viscosity of the medium is relatively large (greater than 650~1000mm2/s), a rotor pump or a reciprocating pump (gear pump, screw pump) can be considered.
e. When the air content of the medium is 75%, the flow rate is small and the viscosity is less than 37.4mm2/s, the vortex pump can be selected.
f. For occasions with a frequent startup or inconvenient pump filling, pumps with self-priming properties, such as self-priming centrifugal pumps, self-priming vortex pumps, and pneumatic (electric) diaphragm pumps, should be selected.

Selection basis

The selection basis of the pump should be considered from five aspects according to the technological process and water supply and drainage requirements, namely, the liquid delivery volume, the device head, the liquid properties, the pipeline layout, and the operating conditions.

1. Flow rate is one of the important performance data for pump selection, which 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 selecting a pump, take the maximum flow rate as the basis and take into account the normal flow rate. When there is no maximum flow rate, usually 1.1 times the normal flow rate can be taken as the maximum flow rate.

2. The head required by the device system is another important performance data for pump selection. Generally, the head should be enlarged by 5%-10% for selection.

3. Liquid properties, including liquid medium name, physical properties, chemical properties and other properties, physical properties include temperature c density d, viscosity u, solid particle diameter and gas content in the medium, etc., which involve the head of the system, the effective cavitation residual Quantity calculation and suitable pump type: chemical properties, mainly referring to the chemical corrosiveness and toxicity of the liquid medium, are an important basis for selecting pump materials and selecting which type of shaft seal.

4. The pipeline layout conditions of the device system refer to the liquid delivery height, the liquid delivery distance, and the liquid delivery direction, such as the lowest liquid level on the suction side and the highest liquid level on the discharge side, as well as some data such as pipeline specifications and their lengths, materials, pipe fittings specifications, quantities, etc., In order to calculate the system head and check the NPSH.

5. There are many operating conditions, such as liquid operation T, saturated steam force P, suction side pressure PS (absolute), discharge side container pressure PZ, altitude, ambient temperature, whether the operation is intermittent or continuous, and whether the pump position is fixed or removable.

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